Momentary Delay

On 06/08/2015 07:59 AM, Anderson Valadares wrote:

Hi
We are experiencing an intermittent problem in a GIS database from a
client. Some times of the day is as if the PostgreSQL executed the
slowest operations see below an example. The query was performed three
times, twice I canceled and the third time I left it to end. The
consultation took 10 seconds to finish, but the measured execution time
is 20 ms. As we have several queries that run every 2 seconds when this
momentary delay occurs queries accumulate and burst the limit of 203
connections allowed. The interval of "momentary stop" are approximately
2 seconds occurring at random times and during these stoppages occur no
locks and no increased load on the server is identified. There is a job
2/2 seconds locks collection of information, running queries, etc., nmon
also collects information every 2 seconds.

I do not have an answer, but I do have a question. What does:

"There is a job
2/2 seconds locks collection of information, running queries, etc"

mean?

My client asks what causes

these momentary stops? because it affects all operations of the
database? etc. How do I identify what is causing these delays in
executions of operations in the database?

The Server is a IBM P720 128G RAM PostgreSQL 9.2.9 on
powerpc-ibm-aix7.1.0.0, compiled by gcc (GCC) 4.6.4, 64-bit

Evolution of the number of connections for a period

snap_datetime | #connections
----------------------------------------------+-------------
2015-06-05 09:25:00.954731-03 |74
2015-06-05 09:26:00.249187-03 |205
2015-06-05 09:27:00.826874-03 |207
2015-06-05 09:28:00.374666-03 |73
2015-06-05 09:29:00.690696-03 |75

Occurrence of the problem

citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,
gis_via_viagem via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 2555.557 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,
gis_via_viagem via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 2192.572 ms
citgis=# explain analyze select max(dvi_sub.dvi_cod_dados_via_iti) as
dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,
gis_via_viagem via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 10164.015 ms
citgis=# select now();
now
-------------------------------
2015-06-05 09:27:22.006072-03
(1 row)

Time: 0.152 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,
gis_via_viagem via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964443 | 7989813
1060072723 | 7990876
(2 rows)

Time: 5565.175 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,
gis_via_viagem via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964445 | 7989813
1060072725 | 7990876
(2 rows)

Time: 27.944 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,
gis_via_viagem via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964445 | 7989813
1060072727 | 7990876
(2 rows)

Time: 24.428 ms

Greetings
Anderson

--
Adrian Klaver
adrian.klaver@aklaver.com

--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general

2015-06-08 12:30 GMT-03:00 Adrian Klaver <adrian.klaver@aklaver.com>:

On 06/08/2015 07:59 AM, Anderson Valadares wrote:

Hi
We are experiencing an intermittent problem in a GIS database from a
client. Some times of the day is as if the PostgreSQL executed the
slowest operations see below an example. The query was performed three
times, twice I canceled and the third time I left it to end. The
consultation took 10 seconds to finish, but the measured execution time
is 20 ms. As we have several queries that run every 2 seconds when this
momentary delay occurs queries accumulate and burst the limit of 203
connections allowed. The interval of "momentary stop" are approximately
2 seconds occurring at random times and during these stoppages occur no
locks and no increased load on the server is identified. There is a job
2/2 seconds locks collection of information, running queries, etc., nmon
also collects information every 2 seconds.

I do not have an answer, but I do have a question. What does:

"There is a job
2/2 seconds locks collection of information, running queries, etc"

mean?

My client asks what causes

these momentary stops? because it affects all operations of the
database? etc. How do I identify what is causing these delays in
executions of operations in the database?

The Server is a IBM P720 128G RAM PostgreSQL 9.2.9 on
powerpc-ibm-aix7.1.0.0, compiled by gcc (GCC) 4.6.4, 64-bit

Evolution of the number of connections for a period

snap_datetime | #connections
----------------------------------------------+-------------
2015-06-05 09:25:00.954731-03 |74
2015-06-05 09:26:00.249187-03 |205
2015-06-05 09:27:00.826874-03 |207
2015-06-05 09:28:00.374666-03 |73
2015-06-05 09:29:00.690696-03 |75

Occurrence of the problem

citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as
dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,
gis_via_viagem via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 2555.557 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as
dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,
gis_via_viagem via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 2192.572 ms
citgis=# explain analyze select max(dvi_sub.dvi_cod_dados_via_iti) as
dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,
gis_via_viagem via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 10164.015 ms
citgis=# select now();
now
-------------------------------
2015-06-05 09:27:22.006072-03
(1 row)

Time: 0.152 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as
dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,
gis_via_viagem via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964443 | 7989813
1060072723 | 7990876
(2 rows)

Time: 5565.175 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as
dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,
gis_via_viagem via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964445 | 7989813
1060072725 | 7990876
(2 rows)

Time: 27.944 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as
dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,
gis_via_viagem via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964445 | 7989813
1060072727 | 7990876
(2 rows)

Time: 24.428 ms

Greetings
Anderson

--
Adrian Klaver
adrian.klaver@aklaver.com

Adrian
forgiveness for my english the meant "Exists a job run every 2 seconds
capturing information of locks, long running queries, etc."

Anderson

On 06/08/2015 09:25 AM, Anderson Valadares wrote:

2015-06-08 12:30 GMT-03:00 Adrian Klaver <adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>>:

Adrian
forgiveness for my english the meant "Exists a job run every 2 seconds
capturing information of locks, long running queries, etc."

So have you looked at the Postgres logs during these time periods to see
if there is anything relevant?

Anderson

--
Adrian Klaver
adrian.klaver@aklaver.com

--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
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2015-06-08 13:58 GMT-03:00 Adrian Klaver <adrian.klaver@aklaver.com>:

On 06/08/2015 09:25 AM, Anderson Valadares wrote:

2015-06-08 12:30 GMT-03:00 Adrian Klaver <adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>>:

Adrian
forgiveness for my english the meant "Exists a job run every 2 seconds
capturing information of locks, long running queries, etc."

So have you looked at the Postgres logs during these time periods to see
if there is anything relevant?

Anderson

--
Adrian Klaver
adrian.klaver@aklaver.com

I saw the logs and there is nothing wrong.

On Mon, 8 Jun 2015 11:59:31 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

Hi
We are experiencing an intermittent problem in a GIS database from a
client. Some times of the day is as if the PostgreSQL executed the slowest
operations see below an example. The query was performed three times, twice
I canceled and the third time I left it to end. The consultation took 10
seconds to finish, but the measured execution time is 20 ms. As we have
several queries that run every 2 seconds when this momentary delay occurs
queries accumulate and burst the limit of 203 connections allowed. The
interval of "momentary stop" are approximately 2 seconds occurring at
random times and during these stoppages occur no locks and no increased
load on the server is identified. There is a job 2/2 seconds locks
collection of information, running queries, etc., nmon also collects
information every 2 seconds. My client asks what causes these momentary
stops? because it affects all operations of the database? etc. How do I
identify what is causing these delays in executions of operations in the
database?

Number of points to consider:
* Check the contents of pg_locks and see if something is waiting on a
lock when the query is slow.
* Also, ensure log_lock_waits is turned on for the server and check
PostgreSQL's logs for messages about long lock waits.
* Make sure shared_buffers isn't larger than 16G. I've seen issues with
PG 9.X and shared_buffers settings larger than that causing
intermittant stalls.
* Based on the connection behavior you describe, I'm guessing it's a
Tomcat app using some sort of conection pool. Whatever it is, tune
your connection pool settings so that the max size of the pool doesn't
exceed the available PostgreSQL connections. At least that will prevent
errors from happening when the problem occurs.
* The query you you keep cancelling below, run judy EXPLAIN on it (not
EXPLAIN ANALYZE) which will certainly finish and give you a plan
that can be reviewed to help determine what the problem is.
* On the OS, monitor iostat or something else to see if you're
saturating disk capacity when the problem happens.

The Server is a IBM P720 128G RAM PostgreSQL 9.2.9 on
powerpc-ibm-aix7.1.0.0, compiled by gcc (GCC) 4.6.4, 64-bit

Evolution of the number of connections for a period

snap_datetime | #connections
----------------------------------------------+-------------
2015-06-05 09:25:00.954731-03 | 74
2015-06-05 09:26:00.249187-03 | 205
2015-06-05 09:27:00.826874-03 | 207
2015-06-05 09:28:00.374666-03 | 73
2015-06-05 09:29:00.690696-03 | 75

Occurrence of the problem

citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub, gis_via_viagem
via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 2555.557 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub, gis_via_viagem
via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 2192.572 ms
citgis=# explain analyze select max(dvi_sub.dvi_cod_dados_via_iti) as
dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub, gis_via_viagem
via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 10164.015 ms
citgis=# select now();
now
-------------------------------
2015-06-05 09:27:22.006072-03
(1 row)

Time: 0.152 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub, gis_via_viagem
via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964443 | 7989813
1060072723 | 7990876
(2 rows)

Time: 5565.175 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub, gis_via_viagem
via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964445 | 7989813
1060072725 | 7990876
(2 rows)

Time: 27.944 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub, gis_via_viagem
via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964445 | 7989813
1060072727 | 7990876
(2 rows)

Time: 24.428 ms

Greetings

Anderson

--
Bill Moran <wmoran@potentialtech.com>

--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
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Please do not remove the mailing list from replies. See below.

On Fri, 12 Jun 2015 09:21:19 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

2015-06-08 20:33 GMT-03:00 Bill Moran <wmoran@potentialtech.com>:

On Mon, 8 Jun 2015 11:59:31 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

Hi
We are experiencing an intermittent problem in a GIS database from a
client. Some times of the day is as if the PostgreSQL executed the

slowest

operations see below an example. The query was performed three times,

twice

I canceled and the third time I left it to end. The consultation took 10
seconds to finish, but the measured execution time is 20 ms. As we have
several queries that run every 2 seconds when this momentary delay occurs
queries accumulate and burst the limit of 203 connections allowed. The
interval of "momentary stop" are approximately 2 seconds occurring at
random times and during these stoppages occur no locks and no increased
load on the server is identified. There is a job 2/2 seconds locks
collection of information, running queries, etc., nmon also collects
information every 2 seconds. My client asks what causes these momentary
stops? because it affects all operations of the database? etc. How do I
identify what is causing these delays in executions of operations in the
database?

Number of points to consider:
* Check the contents of pg_locks and see if something is waiting on a
lock when the query is slow.

There is nothing waiting when the query is slow, see:

snap_datetime | waiting | count
-------------------------------+---------+-------
2015-06-05 09:25:00.954731-03 | f | 74
2015-06-05 09:26:00.249187-03 | f | 205
2015-06-05 09:27:00.826874-03 | f | 207

I don't know what that means. Since you don't show the query that
generated that output, I have no idea if your statement is valid, or
if you're running a query that will inherently produce incorrect
results.

* Also, ensure log_lock_waits is turned on for the server and check

PostgreSQL's logs for messages about long lock waits.

There is also nothing

This is even worse than the previous statement. What did you _do_ to
determine this?

Since you're unable to diagnose and fix the problem on your own, the
possibility exists that the problem is with your diagnostic steps. If
you don't share the details of those steps, I have no way to help you
with them.

* Based on the connection behavior you describe, I'm guessing it's a
Tomcat app using some sort of conection pool. Whatever it is, tune
your connection pool settings so that the max size of the pool doesn't
exceed the available PostgreSQL connections. At least that will prevent
errors from happening when the problem occurs.

Yes it is a tomcat application using connection pooling and will be set to
not exceed the limit of PostgreSQL connections, but the central point is
that the number of connections has increased due to what I am calling
"momentary stoppages"

I understand that. I made the suggestion as a temporary fix to reduce
the impact until you are able to fix the actual cause.

* The query you you keep cancelling below, run just EXPLAIN on it (not
EXPLAIN ANALYZE) which will certainly finish and give you a plan
that can be reviewed to help determine what the problem is.

Explain plan in http://explain.depesz.com/s/bWw

I'm confused. The query at that URL only took 10ms to complete, which
doesn't seem at all unreasonable.

* On the OS, monitor iostat or something else to see if you're

saturating disk capacity when the problem happens.

The OS is also being monitored and there occurs no saturation.

Again, without any details, it's possible that there is a problem
in your monitoring.

The Server is a IBM P720 128G RAM PostgreSQL 9.2.9 on

powerpc-ibm-aix7.1.0.0, compiled by gcc (GCC) 4.6.4, 64-bit

Evolution of the number of connections for a period

snap_datetime | #connections
----------------------------------------------+-------------
2015-06-05 09:25:00.954731-03 | 74
2015-06-05 09:26:00.249187-03 | 205
2015-06-05 09:27:00.826874-03 | 207
2015-06-05 09:28:00.374666-03 | 73
2015-06-05 09:29:00.690696-03 | 75

Occurrence of the problem

citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub, gis_via_viagem
via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 2555.557 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub, gis_via_viagem
via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 2192.572 ms
citgis=# explain analyze select max(dvi_sub.dvi_cod_dados_via_iti) as
dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub, gis_via_viagem
via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 10164.015 ms
citgis=# select now();
now
-------------------------------
2015-06-05 09:27:22.006072-03
(1 row)

Time: 0.152 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub, gis_via_viagem
via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964443 | 7989813
1060072723 | 7990876
(2 rows)

Time: 5565.175 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub, gis_via_viagem
via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964445 | 7989813
1060072725 | 7990876
(2 rows)

Time: 27.944 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub, gis_via_viagem
via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9 hours'
and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964445 | 7989813
1060072727 | 7990876
(2 rows)

Time: 24.428 ms

Greetings

Anderson

--
Bill Moran <wmoran@potentialtech.com>

--
Bill Moran <wmoran@potentialtech.com>

--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general

2015-06-12 19:56 GMT-03:00 Bill Moran <wmoran@potentialtech.com>:

Please do not remove the mailing list from replies. See below.

On Fri, 12 Jun 2015 09:21:19 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

2015-06-08 20:33 GMT-03:00 Bill Moran <wmoran@potentialtech.com>:

On Mon, 8 Jun 2015 11:59:31 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

Hi
We are experiencing an intermittent problem in a GIS database from a
client. Some times of the day is as if the PostgreSQL executed the

slowest

operations see below an example. The query was performed three times,

twice

I canceled and the third time I left it to end. The consultation

took 10

seconds to finish, but the measured execution time is 20 ms. As we

have

several queries that run every 2 seconds when this momentary delay

occurs

queries accumulate and burst the limit of 203 connections allowed.

The

interval of "momentary stop" are approximately 2 seconds occurring at
random times and during these stoppages occur no locks and no

increased

load on the server is identified. There is a job 2/2 seconds locks
collection of information, running queries, etc., nmon also collects
information every 2 seconds. My client asks what causes these

momentary

stops? because it affects all operations of the database? etc. How

do I

identify what is causing these delays in executions of operations in

the

database?

Number of points to consider:
* Check the contents of pg_locks and see if something is waiting on a
lock when the query is slow.

There is nothing waiting when the query is slow, see:

snap_datetime | waiting | count
-------------------------------+---------+-------
2015-06-05 09:25:00.954731-03 | f | 74
2015-06-05 09:26:00.249187-03 | f | 205
2015-06-05 09:27:00.826874-03 | f | 207

I don't know what that means. Since you don't show the query that
generated that output, I have no idea if your statement is valid, or
if you're running a query that will inherently produce incorrect
results.

Sorry the information was incomplete. Below is the query that was
performed to extract information from tables that used to monitor the
database.
The snap_datetime column indicates the time that occurred monitoring,
the waiting column tells you whether any connection was on hold and the
column
count tells how many connections existed at the time.

select
s.snap_datetime
,a.waiting
, count(*)
from stat_snapshot s, stat_activity a
where s.snap_id = a.snap_id
and s.snap_datetime >= '2015-06-05 09:25:00'
and s.snap_datetime <= '2015-06-05 09:28:00'
group by
s.snap_datetime
,a.waiting
order by s.snap_datetime
;
snap_datetime | waiting | count
-------------------------------+---------+-------
2015-06-05 09:25:00.954731-03 | f | 74
2015-06-05 09:26:00.249187-03 | f | 205
2015-06-05 09:27:00.826874-03 | f | 207
(3 rows)

* Also, ensure log_lock_waits is turned on for the server and check

PostgreSQL's logs for messages about long lock waits.

There is also nothing

This is even worse than the previous statement. What did you _do_ to
determine this?

Since you're unable to diagnose and fix the problem on your own, the
possibility exists that the problem is with your diagnostic steps. If
you don't share the details of those steps, I have no way to help you
with them.

See the log in
https://github.com/andervalbh/serv-gis01/blob/master/postgresql-2015-06-05_000000.log

* Based on the connection behavior you describe, I'm guessing it's a
Tomcat app using some sort of conection pool. Whatever it is, tune
your connection pool settings so that the max size of the pool

doesn't

exceed the available PostgreSQL connections. At least that will

prevent

errors from happening when the problem occurs.

Yes it is a tomcat application using connection pooling and will be set

to

not exceed the limit of PostgreSQL connections, but the central point is
that the number of connections has increased due to what I am calling
"momentary stoppages"

I understand that. I made the suggestion as a temporary fix to reduce
the impact until you are able to fix the actual cause.

* The query you you keep cancelling below, run just EXPLAIN on it (not
EXPLAIN ANALYZE) which will certainly finish and give you a plan
that can be reviewed to help determine what the problem is.

Explain plan in http://explain.depesz.com/s/bWw

I'm confused. The query at that URL only took 10ms to complete, which
doesn't seem at all unreasonable.

I agree with you and that's why I ask why the delay in the execution at
certain times
as demonstrated above.

* On the OS, monitor iostat or something else to see if you're

saturating disk capacity when the problem happens.

The OS is also being monitored and there occurs no saturation.

Again, without any details, it's possible that there is a problem
in your monitoring.

See the monitoring spreadsheet generated from nmon in
https://github.com/andervalbh/serv-gis01/blob/master/transfacil07_150605_0000.nmon.rar

On Mon, 15 Jun 2015 17:48:54 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

2015-06-12 19:56 GMT-03:00 Bill Moran <wmoran@potentialtech.com>:

Please do not remove the mailing list from replies. See below.

On Fri, 12 Jun 2015 09:21:19 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

2015-06-08 20:33 GMT-03:00 Bill Moran <wmoran@potentialtech.com>:

On Mon, 8 Jun 2015 11:59:31 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

Hi
We are experiencing an intermittent problem in a GIS database from a
client. Some times of the day is as if the PostgreSQL executed the

slowest

operations see below an example. The query was performed three times,

twice

I canceled and the third time I left it to end. The consultation

took 10

seconds to finish, but the measured execution time is 20 ms. As we

have

several queries that run every 2 seconds when this momentary delay

occurs

queries accumulate and burst the limit of 203 connections allowed.

The

interval of "momentary stop" are approximately 2 seconds occurring at
random times and during these stoppages occur no locks and no

increased

load on the server is identified. There is a job 2/2 seconds locks
collection of information, running queries, etc., nmon also collects
information every 2 seconds. My client asks what causes these

momentary

stops? because it affects all operations of the database? etc. How

do I

identify what is causing these delays in executions of operations in

the

database?

Number of points to consider:
* Check the contents of pg_locks and see if something is waiting on a
lock when the query is slow.

There is nothing waiting when the query is slow, see:

snap_datetime | waiting | count
-------------------------------+---------+-------
2015-06-05 09:25:00.954731-03 | f | 74
2015-06-05 09:26:00.249187-03 | f | 205
2015-06-05 09:27:00.826874-03 | f | 207

I don't know what that means. Since you don't show the query that
generated that output, I have no idea if your statement is valid, or
if you're running a query that will inherently produce incorrect
results.

Sorry the information was incomplete. Below is the query that was
performed to extract information from tables that used to monitor the
database.
The snap_datetime column indicates the time that occurred monitoring,
the waiting column tells you whether any connection was on hold and the
column
count tells how many connections existed at the time.

select
s.snap_datetime
,a.waiting
, count(*)
from stat_snapshot s, stat_activity a
where s.snap_id = a.snap_id
and s.snap_datetime >= '2015-06-05 09:25:00'
and s.snap_datetime <= '2015-06-05 09:28:00'
group by
s.snap_datetime
,a.waiting
order by s.snap_datetime
;
snap_datetime | waiting | count
-------------------------------+---------+-------
2015-06-05 09:25:00.954731-03 | f | 74
2015-06-05 09:26:00.249187-03 | f | 205
2015-06-05 09:27:00.826874-03 | f | 207
(3 rows)

Given what I'm seeing above, there's still a lot of information
missing. Those tables are not standard PostgreSQL tables, and I'm
not aware of any tool that creates them, thus I have to assume
it's a cron job or something similar created in-house. Given the
query you ran and the resultant data, my first guess is that the
data in stat_snapshot and stat_activity is worthless: i.e. it's
captured once per minute, and therefore there are 59+ seconds
worth of detail that aren't captured, thus the actual liklihood
that the those tables will contain any indication of the problem
is very low.

* Also, ensure log_lock_waits is turned on for the server and check

PostgreSQL's logs for messages about long lock waits.

There is also nothing

This is even worse than the previous statement. What did you _do_ to
determine this?

Since you're unable to diagnose and fix the problem on your own, the
possibility exists that the problem is with your diagnostic steps. If
you don't share the details of those steps, I have no way to help you
with them.

See the log in
https://github.com/andervalbh/serv-gis01/blob/master/postgresql-2015-06-05_000000.log

Apologies, my above comment was intended to be in regards to the IO load.

However, that log shows that you have massive lock contention. In the early
part of the log a process waits over 5 minutes for a share lock:
2015-06-05 05:51:32 BRT [44236822] - [10.57.1.26] [14-1] db=citgis,user=opegis LOG: process 44236822 acquired ShareLock on transaction 3090377758 after 374146.817 ms

Without seeing the source of the PL/pgSQL functions that seem to be
causing the problem, I can only suggest that you review those functions
for excessive locking and inefficient access. I'm going to guess, with
the large number of AccessExclusiveLocks in the log, that the functions
are doing explicit locking, and not doing so in an efficient manner.

* Based on the connection behavior you describe, I'm guessing it's a
Tomcat app using some sort of conection pool. Whatever it is, tune
your connection pool settings so that the max size of the pool

doesn't

exceed the available PostgreSQL connections. At least that will

prevent

errors from happening when the problem occurs.

Yes it is a tomcat application using connection pooling and will be set

to

not exceed the limit of PostgreSQL connections, but the central point is
that the number of connections has increased due to what I am calling
"momentary stoppages"

I understand that. I made the suggestion as a temporary fix to reduce
the impact until you are able to fix the actual cause.

* The query you you keep cancelling below, run just EXPLAIN on it (not
EXPLAIN ANALYZE) which will certainly finish and give you a plan
that can be reviewed to help determine what the problem is.

Explain plan in http://explain.depesz.com/s/bWw

I'm confused. The query at that URL only took 10ms to complete, which
doesn't seem at all unreasonable.

I agree with you and that's why I ask why the delay in the execution at
certain times
as demonstrated above.

* On the OS, monitor iostat or something else to see if you're

saturating disk capacity when the problem happens.

The OS is also being monitored and there occurs no saturation.

Again, without any details, it's possible that there is a problem
in your monitoring.

See the monitoring spreadsheet generated from nmon in
https://github.com/andervalbh/serv-gis01/blob/master/transfacil07_150605_0000.nmon.rar

The Server is a IBM P720 128G RAM PostgreSQL 9.2.9 on

powerpc-ibm-aix7.1.0.0, compiled by gcc (GCC) 4.6.4, 64-bit

Evolution of the number of connections for a period

snap_datetime | #connections
----------------------------------------------+-------------
2015-06-05 09:25:00.954731-03 | 74
2015-06-05 09:26:00.249187-03 | 205
2015-06-05 09:27:00.826874-03 | 207
2015-06-05 09:28:00.374666-03 | 73
2015-06-05 09:29:00.690696-03 | 75

Occurrence of the problem

citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,

gis_via_viagem

via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9

hours'

and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 2555.557 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,

gis_via_viagem

via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9

hours'

and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 2192.572 ms
citgis=# explain analyze select max(dvi_sub.dvi_cod_dados_via_iti) as
dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,

gis_via_viagem

via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9

hours'

and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 10164.015 ms
citgis=# select now();
now
-------------------------------
2015-06-05 09:27:22.006072-03
(1 row)

Time: 0.152 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,

gis_via_viagem

via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9

hours'

and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964443 | 7989813
1060072723 | 7990876
(2 rows)

Time: 5565.175 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,

gis_via_viagem

via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9

hours'

and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964445 | 7989813
1060072725 | 7990876
(2 rows)

Time: 27.944 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,

gis_via_viagem

via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem = via_sub.via_cod_viagem
and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9

hours'

and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964445 | 7989813
1060072727 | 7990876
(2 rows)

Time: 24.428 ms

Greetings

Anderson

--
Bill Moran <wmoran@potentialtech.com>

--
Bill Moran <wmoran@potentialtech.com>

--
Bill Moran <wmoran@potentialtech.com>

--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
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2015-06-15 18:19 GMT-03:00 Bill Moran <wmoran@potentialtech.com>:

On Mon, 15 Jun 2015 17:48:54 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

2015-06-12 19:56 GMT-03:00 Bill Moran <wmoran@potentialtech.com>:

Please do not remove the mailing list from replies. See below.

On Fri, 12 Jun 2015 09:21:19 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

2015-06-08 20:33 GMT-03:00 Bill Moran <wmoran@potentialtech.com>:

On Mon, 8 Jun 2015 11:59:31 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

Hi
We are experiencing an intermittent problem in a GIS database

from a

client. Some times of the day is as if the PostgreSQL executed

the

slowest

operations see below an example. The query was performed three

times,

twice

I canceled and the third time I left it to end. The consultation

took 10

seconds to finish, but the measured execution time is 20 ms. As

we

have

several queries that run every 2 seconds when this momentary

delay

occurs

queries accumulate and burst the limit of 203 connections

allowed.

The

interval of "momentary stop" are approximately 2 seconds

occurring at

random times and during these stoppages occur no locks and no

increased

load on the server is identified. There is a job 2/2 seconds

locks

collection of information, running queries, etc., nmon also

collects

information every 2 seconds. My client asks what causes these

momentary

stops? because it affects all operations of the database? etc.

How

do I

identify what is causing these delays in executions of

operations in

the

database?

Number of points to consider:
* Check the contents of pg_locks and see if something is waiting

on a

lock when the query is slow.

There is nothing waiting when the query is slow, see:

snap_datetime | waiting | count
-------------------------------+---------+-------
2015-06-05 09:25:00.954731-03 | f | 74
2015-06-05 09:26:00.249187-03 | f | 205
2015-06-05 09:27:00.826874-03 | f | 207

I don't know what that means. Since you don't show the query that
generated that output, I have no idea if your statement is valid, or
if you're running a query that will inherently produce incorrect
results.

Sorry the information was incomplete. Below is the query that was
performed to extract information from tables that used to monitor the
database.
The snap_datetime column indicates the time that occurred monitoring,
the waiting column tells you whether any connection was on hold and the
column
count tells how many connections existed at the time.

select
s.snap_datetime
,a.waiting
, count(*)
from stat_snapshot s, stat_activity a
where s.snap_id = a.snap_id
and s.snap_datetime >= '2015-06-05 09:25:00'
and s.snap_datetime <= '2015-06-05 09:28:00'
group by
s.snap_datetime
,a.waiting
order by s.snap_datetime
;
snap_datetime | waiting | count
-------------------------------+---------+-------
2015-06-05 09:25:00.954731-03 | f | 74
2015-06-05 09:26:00.249187-03 | f | 205
2015-06-05 09:27:00.826874-03 | f | 207
(3 rows)

Given what I'm seeing above, there's still a lot of information
missing. Those tables are not standard PostgreSQL tables, and I'm
not aware of any tool that creates them, thus I have to assume
it's a cron job or something similar created in-house. Given the
query you ran and the resultant data, my first guess is that the
data in stat_snapshot and stat_activity is worthless: i.e. it's
captured once per minute, and therefore there are 59+ seconds
worth of detail that aren't captured, thus the actual liklihood
that the those tables will contain any indication of the problem
is very low.

Yes it is a cron, created at home, running every 1 hour gathering
information from PostgreSQL tables (pg_stat_activity, pg_locks, etc).
How to improve the collection of information PostgreSQL?

* Also, ensure log_lock_waits is turned on for the server and check

PostgreSQL's logs for messages about long lock waits.

There is also nothing

This is even worse than the previous statement. What did you _do_ to
determine this?

Since you're unable to diagnose and fix the problem on your own, the
possibility exists that the problem is with your diagnostic steps. If
you don't share the details of those steps, I have no way to help you
with them.

See the log in

https://github.com/andervalbh/serv-gis01/blob/master/postgresql-2015-06-05_000000.log

Apologies, my above comment was intended to be in regards to the IO load.

However, that log shows that you have massive lock contention. In the early
part of the log a process waits over 5 minutes for a share lock:
2015-06-05 05:51:32 BRT [44236822] - [10.57.1.26] [14-1]
db=citgis,user=opegis LOG: process 44236822 acquired ShareLock on
transaction 3090377758 after 374146.817 ms

Without seeing the source of the PL/pgSQL functions that seem to be
causing the problem, I can only suggest that you review those functions
for excessive locking and inefficient access. I'm going to guess, with
the large number of AccessExclusiveLocks in the log, that the functions
are doing explicit locking, and not doing so in an efficient manner.

This function PL / pgSQL has been fixed, but see that during the period in
which the SQL presenting slowness problem (between 9:26:00 and 9:27:00)
there is no block occurrences.

On Wed, 17 Jun 2015 10:33:37 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

2015-06-15 18:19 GMT-03:00 Bill Moran <wmoran@potentialtech.com>:

On Mon, 15 Jun 2015 17:48:54 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

2015-06-12 19:56 GMT-03:00 Bill Moran <wmoran@potentialtech.com>:

Please do not remove the mailing list from replies. See below.

On Fri, 12 Jun 2015 09:21:19 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

2015-06-08 20:33 GMT-03:00 Bill Moran <wmoran@potentialtech.com>:

On Mon, 8 Jun 2015 11:59:31 -0300
Anderson Valadares <andervalbh@gmail.com> wrote:

Hi
We are experiencing an intermittent problem in a GIS database

from a

client. Some times of the day is as if the PostgreSQL executed

the

slowest

operations see below an example. The query was performed three

times,

twice

I canceled and the third time I left it to end. The consultation

took 10

seconds to finish, but the measured execution time is 20 ms. As

we

have

several queries that run every 2 seconds when this momentary

delay

occurs

queries accumulate and burst the limit of 203 connections

allowed.

The

interval of "momentary stop" are approximately 2 seconds

occurring at

random times and during these stoppages occur no locks and no

increased

load on the server is identified. There is a job 2/2 seconds

locks

collection of information, running queries, etc., nmon also

collects

information every 2 seconds. My client asks what causes these

momentary

stops? because it affects all operations of the database? etc.

How

do I

identify what is causing these delays in executions of

operations in

the

database?

Number of points to consider:
* Check the contents of pg_locks and see if something is waiting

on a

lock when the query is slow.

There is nothing waiting when the query is slow, see:

snap_datetime | waiting | count
-------------------------------+---------+-------
2015-06-05 09:25:00.954731-03 | f | 74
2015-06-05 09:26:00.249187-03 | f | 205
2015-06-05 09:27:00.826874-03 | f | 207

I don't know what that means. Since you don't show the query that
generated that output, I have no idea if your statement is valid, or
if you're running a query that will inherently produce incorrect
results.

Sorry the information was incomplete. Below is the query that was
performed to extract information from tables that used to monitor the
database.
The snap_datetime column indicates the time that occurred monitoring,
the waiting column tells you whether any connection was on hold and the
column
count tells how many connections existed at the time.

select
s.snap_datetime
,a.waiting
, count(*)
from stat_snapshot s, stat_activity a
where s.snap_id = a.snap_id
and s.snap_datetime >= '2015-06-05 09:25:00'
and s.snap_datetime <= '2015-06-05 09:28:00'
group by
s.snap_datetime
,a.waiting
order by s.snap_datetime
;
snap_datetime | waiting | count
-------------------------------+---------+-------
2015-06-05 09:25:00.954731-03 | f | 74
2015-06-05 09:26:00.249187-03 | f | 205
2015-06-05 09:27:00.826874-03 | f | 207
(3 rows)

Given what I'm seeing above, there's still a lot of information
missing. Those tables are not standard PostgreSQL tables, and I'm
not aware of any tool that creates them, thus I have to assume
it's a cron job or something similar created in-house. Given the
query you ran and the resultant data, my first guess is that the
data in stat_snapshot and stat_activity is worthless: i.e. it's
captured once per minute, and therefore there are 59+ seconds
worth of detail that aren't captured, thus the actual liklihood
that the those tables will contain any indication of the problem
is very low.

Yes it is a cron, created at home, running every 1 hour gathering
information from PostgreSQL tables (pg_stat_activity, pg_locks, etc).
How to improve the collection of information PostgreSQL?

Look at the log file, details of what is going on are being recorded
as they happen.

However, given your statement below (claiming that nothing happened
during the observed slowdown between 9:26 and 9:27) you may want to
find someone who is actually capable of interpreting the log output,
as there are dozens of indicators of what's wrong. Immediately after
the problem disappears, a number of queries finish after spending a
lot of time executing, in addition to a number of complaints of long
lock waits. So all those queries were fighting each other and when
they finally untangled themselves and got their work done, everything
started running smoothly again.

I would look at fct_sinotico_simplificado(), as it seems to be putting
an undue load on the system. FCT_PAINEL_CCO_VEICULOS_GMAPS() might
also be a problem, but it seems less prevalent. I don't know what
language those function names are in, so I can't really guess at
what they do to make any more detailed recommendations.

Additionally, there is a checkpoint in the middle of the problem
period that took 44 seconds to write 600M to disk. That seems to
contradict your earlier statement that IO isn't being maxed out and
makes me doubt that your IO monitoring is effective.

My overall guess is that you have some poorly written code, both on
the Java side and on the database trigger/function side; but that
under normal usage the hardware is sufficient to keep up. However,
when you have a brief spike in activity, the inefficiencies create
a cascading performance problem. I've seen this before at a previous
job, and the high-level problem was that most developers are good
enough to throw something together that will work, but not talented
and experienced enough to write something truely efficient.

Lock down your connection pool to keep it smaller. Look at where you
can do caching on the Java side to avoid rapid-fire duplicate queries.
Look at limiting inserts to busy tables to a single worker thread that
has a queueing structure so that it can absorb spike loads and spread
the load on the DB out more evenly. Implement SOA so that frequently
accessed data can be kept in Java's memory on the services instead of
_always_ having to query the database. These are just a few of the
techniques available to fix problems like this.

* Also, ensure log_lock_waits is turned on for the server and check

PostgreSQL's logs for messages about long lock waits.

There is also nothing

This is even worse than the previous statement. What did you _do_ to
determine this?

Since you're unable to diagnose and fix the problem on your own, the
possibility exists that the problem is with your diagnostic steps. If
you don't share the details of those steps, I have no way to help you
with them.

See the log in

https://github.com/andervalbh/serv-gis01/blob/master/postgresql-2015-06-05_000000.log

Apologies, my above comment was intended to be in regards to the IO load.

However, that log shows that you have massive lock contention. In the early
part of the log a process waits over 5 minutes for a share lock:
2015-06-05 05:51:32 BRT [44236822] - [10.57.1.26] [14-1]
db=citgis,user=opegis LOG: process 44236822 acquired ShareLock on
transaction 3090377758 after 374146.817 ms

Without seeing the source of the PL/pgSQL functions that seem to be
causing the problem, I can only suggest that you review those functions
for excessive locking and inefficient access. I'm going to guess, with
the large number of AccessExclusiveLocks in the log, that the functions
are doing explicit locking, and not doing so in an efficient manner.

This function PL / pgSQL has been fixed, but see that during the period in
which the SQL presenting slowness problem (between 9:26:00 and 9:27:00)
there is no block occurrences.

* Based on the connection behavior you describe, I'm guessing it's

a

Tomcat app using some sort of conection pool. Whatever it is,

tune

your connection pool settings so that the max size of the pool

doesn't

exceed the available PostgreSQL connections. At least that will

prevent

errors from happening when the problem occurs.

Yes it is a tomcat application using connection pooling and will be

set

to

not exceed the limit of PostgreSQL connections, but the central

point is

that the number of connections has increased due to what I am calling
"momentary stoppages"

I understand that. I made the suggestion as a temporary fix to reduce
the impact until you are able to fix the actual cause.

* The query you you keep cancelling below, run just EXPLAIN on it

(not

EXPLAIN ANALYZE) which will certainly finish and give you a plan
that can be reviewed to help determine what the problem is.

Explain plan in http://explain.depesz.com/s/bWw

I'm confused. The query at that URL only took 10ms to complete, which
doesn't seem at all unreasonable.

I agree with you and that's why I ask why the delay in the execution at
certain times
as demonstrated above.

* On the OS, monitor iostat or something else to see if you're

saturating disk capacity when the problem happens.

The OS is also being monitored and there occurs no saturation.

Again, without any details, it's possible that there is a problem
in your monitoring.

See the monitoring spreadsheet generated from nmon in

https://github.com/andervalbh/serv-gis01/blob/master/transfacil07_150605_0000.nmon.rar

The Server is a IBM P720 128G RAM PostgreSQL 9.2.9 on

powerpc-ibm-aix7.1.0.0, compiled by gcc (GCC) 4.6.4, 64-bit

Evolution of the number of connections for a period

snap_datetime | #connections
----------------------------------------------+-------------
2015-06-05 09:25:00.954731-03 | 74
2015-06-05 09:26:00.249187-03 | 205
2015-06-05 09:27:00.826874-03 | 207
2015-06-05 09:28:00.374666-03 | 73
2015-06-05 09:29:00.690696-03 | 75

Occurrence of the problem

citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,

gis_via_viagem

via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem =

via_sub.via_cod_viagem

and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9

hours'

and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 2555.557 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,

gis_via_viagem

via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem =

via_sub.via_cod_viagem

and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9

hours'

and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 2192.572 ms
citgis=# explain analyze select

max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,
dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,

gis_via_viagem

via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem =

via_sub.via_cod_viagem

and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9

hours'

and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
Cancel request sent
ERROR: canceling statement due to user request
Time: 10164.015 ms
citgis=# select now();
now
-------------------------------
2015-06-05 09:27:22.006072-03
(1 row)

Time: 0.152 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,

gis_via_viagem

via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem =

via_sub.via_cod_viagem

and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9

hours'

and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964443 | 7989813
1060072723 | 7990876
(2 rows)

Time: 5565.175 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,

gis_via_viagem

via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem =

via_sub.via_cod_viagem

and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9

hours'

and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964445 | 7989813
1060072725 | 7990876
(2 rows)

Time: 27.944 ms
citgis=# select max(dvi_sub.dvi_cod_dados_via_iti) as

dvi_cod_dados_via_iti,

dvi_sub.via_cod_viagem
from gis_dvi_dados_viagem_itinerario dvi_sub,

gis_via_viagem

via_sub, gis_iti_itinerario iti_sub
where dvi_sub.via_cod_viagem =

via_sub.via_cod_viagem

and via_sub.via_status_viagem = 'A'
and via_sub.via_dt_hora_ini > now() - interval '9

hours'

and iti_sub.lin_cod_linha = 389
and iti_sub.iti_sentido_itinerario = 'I'
and iti_sub.iti_cod_itinerario_linha =
via_sub.iti_cod_itinerario_linha
and dvi_sub.vlo_cod_localizacao is not null
group by dvi_sub.via_cod_viagem,
iti_sub.iti_cod_itinerario_linha, via_sub.equ_cod_eqpto
;
dvi_cod_dados_via_iti | via_cod_viagem
-----------------------+----------------
1059964445 | 7989813
1060072727 | 7990876
(2 rows)

Time: 24.428 ms

Greetings

Anderson

--
Bill Moran <wmoran@potentialtech.com>

--
Bill Moran <wmoran@potentialtech.com>

--
Bill Moran <wmoran@potentialtech.com>

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Bill Moran

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