pg_upgrade —link does it remove table bloat
When using the pg_upgrade link method to upgrade Postgres a major version. Let’s say 9.3 to 11.6 on Centos Linux. Will table bloat carry over to the new version. I know using —link will use hard link pointers to the new data. So I assume all table bloat will carry over to the new version. I also know that pg_upgrade will reset statistics, so does the table remain bloated but statistics show otherwise? Can Someone please help me answer this? Or link where it’s outlined in the manual. Thanks as always.
Jason Ralph
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On 2/13/20 4:31 AM, Jason Ralph wrote:
When using the pg_upgrade link method to upgrade Postgres a major
version. Let�s say 9.3 to 11.6 on Centos Linux. Will table bloat carry
over to the new version. I know using �link will use hard link pointers
to the new data. So I assume all table bloat will carry over to the new
version. I also know that pg_upgrade will reset statistics, so does the
table remain bloated but statistics show otherwise? Can Someone please
help me answer this? Or link where it�s outlined in the manual. Thanks
as always.
Well table bloat and table statistics are two different things. Bloat is
the accumulation of dead or potentially dead tuples whose space has not
been marked as available for reuse by VACUUM or whose space has been
returned to the OS with VACUUM FULL. For more information see:
https://www.postgresql.org/docs/12/routine-vacuuming.html
I would think it would not matter if the files where copied or linked if
the space was being held open as result of regular VACUUM.
Statistics are just that statistics collected about the distribution of
values in the table. For more information see:
https://www.postgresql.org/docs/12/monitoring-stats.html
https://www.postgresql.org/docs/12/planner-stats-details.html
They are collected as part of the autovacuum process or by running
ANALYZE by itself or with VACUUM. FYI, pg_upgrade does not
automatically update the statistics, it just writes a script that you
can then run manually to do that:
https://www.postgresql.org/docs/12/pgupgrade.html
14.Statistics
Because optimizer statistics are not transferred by pg_upgrade, you will
be instructed to run a command to regenerate that information at the end
of the upgrade. You might need to set connection parameters to match
your new cluster.
Jason Ralph
--
Adrian Klaver
adrian.klaver@aklaver.com
There is more than one type of statistics though. Stats on the distribution
of data is easily recreated with analyze table_name or analyzing the whole
database. What about the stats on how many rows have been inserted or
updated since the last (auto)vacuum and that will be used to trigger
autovacuum? Are those set back to zero by an upgrade? I would assume usage
counts like how many times an index scan has been done would be reset, but
if the numbers in pg_stat_user_tables like n_tup_upd or n_tup_del are
zero'd out during an upgrade, than it would seem like a manual vacuum would
always be a good idea to ensure a table wasn't 99% of the way to needing
one and then the stats got reset by upgrading.
Well table bloat and table statistics are two different things. Bloat is the accumulation of dead or potentially dead tuples whose space has not been marked > as available for reuse by VACUUM or whose space has been returned to the OS with VACUUM FULL. For more information see:
Thanks for the helpful response @Adrian Klaver,
Let me try to rephrase my question,
If a table has bloat before the upgrade, autvacuum was not aggressive enough, once pg_upgrade is complete, the same table will contain the same amount of bloat(dead tuples)? Meaning its not the same as pg_dump / pg_restore since it’s a hard link to the previous data location. Pg_upgrade with link will not recreate the table.
Jason Ralph
-----Original Message-----
From: Adrian Klaver <adrian.klaver@aklaver.com>
Sent: Thursday, February 13, 2020 10:46 AM
To: Jason Ralph <jralph@affinitysolutions.com>; pgsql-general@lists.postgresql.org
Subject: Re: pg_upgrade —link does it remove table bloat
On 2/13/20 4:31 AM, Jason Ralph wrote:
When using the pg_upgrade link method to upgrade Postgres a major
version. Let’s say 9.3 to 11.6 on Centos Linux. Will table bloat carry
over to the new version. I know using —link will use hard link
pointers to the new data. So I assume all table bloat will carry over
to the new version. I also know that pg_upgrade will reset statistics,
so does the table remain bloated but statistics show otherwise? Can
Someone please help me answer this? Or link where it’s outlined in the
manual. Thanks as always.
Well table bloat and table statistics are two different things. Bloat is the accumulation of dead or potentially dead tuples whose space has not been marked as available for reuse by VACUUM or whose space has been returned to the OS with VACUUM FULL. For more information see:
I would think it would not matter if the files where copied or linked if the space was being held open as result of regular VACUUM.
Statistics are just that statistics collected about the distribution of values in the table. For more information see:
They are collected as part of the autovacuum process or by running ANALYZE by itself or with VACUUM. FYI, pg_upgrade does not automatically update the statistics, it just writes a script that you can then run manually to do that:
14.Statistics
Because optimizer statistics are not transferred by pg_upgrade, you will be instructed to run a command to regenerate that information at the end of the upgrade. You might need to set connection parameters to match your new cluster.
Jason Ralph
--
Adrian Klaver
adrian.klaver@aklaver.com
This message contains confidential information and is intended only for the individual named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately by e-mail if you have received this e-mail by mistake and delete this e-mail from your system. E-mail transmission cannot be guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore does not accept liability for any errors or omissions in the contents of this message, which arise as a result of e-mail transmission. If verification is required please request a hard-copy version.
On 2/13/20 10:04 AM, Jason Ralph wrote:
Well table bloat and table statistics are two different things. Bloat is the accumulation of dead or potentially dead tuples whose space has not been marked > as available for reuse by VACUUM or whose space has been returned to the OS with VACUUM FULL. For more information see:
Thanks for the helpful response @Adrian Klaver,
Let me try to rephrase my question,
If a table has bloat before the upgrade, autvacuum was not aggressive enough, once pg_upgrade is complete, the same table will contain the same amount of bloat(dead tuples)? Meaning its not the same as pg_dump / pg_restore since it�s a hard link to the previous data location. Pg_upgrade with link will not recreate the table.
Yes pg_upgrade is a transfer of the binary data(sort of) whereas
pg_dump/restore is a logical transfer. So pg_upgrade via copy/clone/link
will not recreate user tables. For a good overview see IMPLEMENTATION
file in src:
Jason Ralph
--
Adrian Klaver
adrian.klaver@aklaver.com
There is more than one type of statistics though. Stats on the distribution of data is easily recreated with analyze table_name or analyzing the whole >database. What about the stats on how many rows have been inserted or updated since the last (auto)vacuum and that will be used to trigger autovacuum? >Are those set back to zero by an upgrade? I would assume usage counts like how many times an index scan has been done would be reset, but if the >numbers in pg_stat_user_tables like n_tup_upd or n_tup_del are zero'd out during an upgrade, than it would seem like a manual vacuum would always be a >good idea to ensure a table wasn't 99% of the way to needing one and then the stats got reset by upgrading.
I agree @Michael Lewis<mailto:mlewis@entrata.com>, thank you for this comment.
I am thinking a vacuum full is what I am going to need. Or pg_dump / pg_restore. I have tuned auto vacuum after the upgrade to be aggressive, it finishes fine after a couple hours on a large table, statistics look good on the pg_stat_user_tables. However, when I run the bloat check from the wiki https://wiki.postgresql.org/wiki/Show_database_bloat it still shows bloat. Thinking it may be left over from before the pg_upgrade and auto vacuum tuning.
Best,
Jason Ralph
From: Michael Lewis <mlewis@entrata.com>
Sent: Thursday, February 13, 2020 1:02 PM
To: Adrian Klaver <adrian.klaver@aklaver.com>
Cc: Jason Ralph <jralph@affinitysolutions.com>; pgsql-general@lists.postgresql.org
Subject: Re: pg_upgrade —link does it remove table bloat
There is more than one type of statistics though. Stats on the distribution of data is easily recreated with analyze table_name or analyzing the whole database. What about the stats on how many rows have been inserted or updated since the last (auto)vacuum and that will be used to trigger autovacuum? Are those set back to zero by an upgrade? I would assume usage counts like how many times an index scan has been done would be reset, but if the numbers in pg_stat_user_tables like n_tup_upd or n_tup_del are zero'd out during an upgrade, than it would seem like a manual vacuum would always be a good idea to ensure a table wasn't 99% of the way to needing one and then the stats got reset by upgrading.
This message contains confidential information and is intended only for the individual named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately by e-mail if you have received this e-mail by mistake and delete this e-mail from your system. E-mail transmission cannot be guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore does not accept liability for any errors or omissions in the contents of this message, which arise as a result of e-mail transmission. If verification is required please request a hard-copy version.
On 2/13/20 11:07 AM, Jason Ralph wrote:
There is more than one type of statistics though. Stats on the
distribution of data is easily recreated with analyze table_name or
analyzing the whole >database. What about the stats on how many rows
have been inserted or updated since the last (auto)vacuum and that will
be used to trigger autovacuum? >Are those set back to zero by an
upgrade? I would assume usage counts like how many times an index scan
has been done would be reset, but if the >numbers in pg_stat_user_tables
like n_tup_upd or n_tup_del are zero'd out during an upgrade, than it
would seem like a manual vacuum would always be a >good idea to ensure a
table wasn't 99% of the way to needing one and then the stats got reset
by upgrading.I agree @Michael Lewis <mailto:mlewis@entrata.com>, thank you for this
comment.I am thinking a vacuum full is what I am going to need. Or pg_dump /
pg_restore. I have tuned auto vacuum after the upgrade to be aggressive,
it finishes fine after a couple hours on a large table, statistics look
good on the pg_stat_user_tables. However, when I run the bloat check
from the wiki https://wiki.postgresql.org/wiki/Show_database_bloat it
still shows bloat. Thinking it may be left over from before the
pg_upgrade and auto vacuum tuning.
What values are you getting?
The script you are using comes from this:
https://bucardo.org/check_postgres/check_postgres.pl.html#bloat
"If you want to output the bloat ratio instead (how many times larger
the relation is compared to how large it should be),..."
So I'm pretty sure bloat is where tbloat > 1.0.
Best,
*Jason Ralph*
*From:* Michael Lewis <mlewis@entrata.com>
*Sent:* Thursday, February 13, 2020 1:02 PM
*To:* Adrian Klaver <adrian.klaver@aklaver.com>
*Cc:* Jason Ralph <jralph@affinitysolutions.com>;
pgsql-general@lists.postgresql.org
*Subject:* Re: pg_upgrade —link does it remove table bloatThere is more than one type of statistics though. Stats on the
distribution of data is easily recreated with analyze table_name or
analyzing the whole database. What about the stats on how many rows have
been inserted or updated since the last (auto)vacuum and that will be
used to trigger autovacuum? Are those set back to zero by an upgrade? I
would assume usage counts like how many times an index scan has been
done would be reset, but if the numbers in pg_stat_user_tables like
n_tup_upd or n_tup_del are zero'd out during an upgrade, than it would
seem like a manual vacuum would always be a good idea to ensure a table
wasn't 99% of the way to needing one and then the stats got reset by
upgrading.This message contains confidential information and is intended only for
the individual named. If you are not the named addressee you should not
disseminate, distribute or copy this e-mail. Please notify the sender
immediately by e-mail if you have received this e-mail by mistake and
delete this e-mail from your system. E-mail transmission cannot be
guaranteed to be secure or error-free as information could be
intercepted, corrupted, lost, destroyed, arrive late or incomplete, or
contain viruses. The sender therefore does not accept liability for any
errors or omissions in the contents of this message, which arise as a
result of e-mail transmission. If verification is required please
request a hard-copy version.
--
Adrian Klaver
adrian.klaver@aklaver.com
@Adrian Klaver,
I was concerned with the 1.4 value of tbloat and wastedbytes value, then again the last autovacuum was at 2020-02-13 02:25:22.533372-05 and I took this snapshot at 3:44PMEST. So it may be ok, what do you think?
current_database | schemaname | tablename | tbloat | wastedbytes | iname | ibloat | wastedibytes
notimportant | public | members | 1.4 | 3080314880 | members_cobrid | 0.2 | 0
notimportant=# select * from pg_stat_user_tables where relname = 'members';
-[ RECORD 1 ]-------+------------------------------
relid | 2045245
schemaname | public
relname | members
seq_scan | 55065
seq_tup_read | 201069350222
idx_scan | 5349501175
idx_tup_fetch | 7201402647
n_tup_ins | 910616
n_tup_upd | 46730942
n_tup_del | 1
n_tup_hot_upd | 41845682
n_live_tup | 18262438
n_dead_tup | 14740
n_mod_since_analyze | 2476
last_vacuum | 2019-10-13 01:01:40.587534-04
last_autovacuum | 2020-02-13 02:25:22.533372-05
last_analyze | 2019-10-13 01:01:41.916929-04
last_autoanalyze | 2020-02-13 13:44:46.273096-05
vacuum_count | 15
autovacuum_count | 92
analyze_count | 15
autoanalyze_count | 243
Jason Ralph
-----Original Message-----
From: Adrian Klaver <adrian.klaver@aklaver.com>
Sent: Thursday, February 13, 2020 3:19 PM
To: Jason Ralph <jralph@affinitysolutions.com>; Michael Lewis <mlewis@entrata.com>
Cc: pgsql-general@lists.postgresql.org
Subject: Re: pg_upgrade —link does it remove table bloat
On 2/13/20 11:07 AM, Jason Ralph wrote:
There is more than one type of statistics though. Stats on the
distribution of data is easily recreated with analyze table_name or
analyzing the whole >database. What about the stats on how many rows
have been inserted or updated since the last (auto)vacuum and that
will be used to trigger autovacuum? >Are those set back to zero by an
upgrade? I would assume usage counts like how many times an index scan
has been done would be reset, but if the >numbers in
pg_stat_user_tables like n_tup_upd or n_tup_del are zero'd out during
an upgrade, than it would seem like a manual vacuum would always be agood idea to ensure a table wasn't 99% of the way to needing one and
then the stats got reset by upgrading.
I agree @Michael Lewis <mailto:mlewis@entrata.com>, thank you for this
comment.I am thinking a vacuum full is what I am going to need. Or pg_dump /
pg_restore. I have tuned auto vacuum after the upgrade to be
aggressive, it finishes fine after a couple hours on a large table,
statistics look good on the pg_stat_user_tables. However, when I run
the bloat check from the wiki
https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwiki
.postgresql.org%2Fwiki%2FShow_database_bloat&data=01%7C01%7Cjralph%40affinitysolutions.com%7C6ead29e3b0bf4238f50e08d7b0c1fd0b%7Cfbf1a257f1104fc19456b0ca3038c6f0%7C1&sdata=d8kSilB5eqJGWujd7tzlX5xaRhm5Z335G34MAO6%2BHOY%3D&reserved=0 it still shows bloat. Thinking it may be left over from before the pg_upgrade and auto vacuum tuning.
What values are you getting?
The script you are using comes from this:
"If you want to output the bloat ratio instead (how many times larger the relation is compared to how large it should be),..."
So I'm pretty sure bloat is where tbloat > 1.0.
Best,
*Jason Ralph*
*From:* Michael Lewis <mlewis@entrata.com>
*Sent:* Thursday, February 13, 2020 1:02 PM
*To:* Adrian Klaver <adrian.klaver@aklaver.com>
*Cc:* Jason Ralph <jralph@affinitysolutions.com>;
pgsql-general@lists.postgresql.org
*Subject:* Re: pg_upgrade —link does it remove table bloatThere is more than one type of statistics though. Stats on the
distribution of data is easily recreated with analyze table_name or
analyzing the whole database. What about the stats on how many rows
have been inserted or updated since the last (auto)vacuum and that
will be used to trigger autovacuum? Are those set back to zero by an
upgrade? I would assume usage counts like how many times an index scan
has been done would be reset, but if the numbers in
pg_stat_user_tables like n_tup_upd or n_tup_del are zero'd out during
an upgrade, than it would seem like a manual vacuum would always be a
good idea to ensure a table wasn't 99% of the way to needing one and
then the stats got reset by upgrading.This message contains confidential information and is intended only
for the individual named. If you are not the named addressee you
should not disseminate, distribute or copy this e-mail. Please notify
the sender immediately by e-mail if you have received this e-mail by
mistake and delete this e-mail from your system. E-mail transmission
cannot be guaranteed to be secure or error-free as information could
be intercepted, corrupted, lost, destroyed, arrive late or incomplete,
or contain viruses. The sender therefore does not accept liability for
any errors or omissions in the contents of this message, which arise
as a result of e-mail transmission. If verification is required please
request a hard-copy version.
--
Adrian Klaver
adrian.klaver@aklaver.com
This message contains confidential information and is intended only for the individual named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately by e-mail if you have received this e-mail by mistake and delete this e-mail from your system. E-mail transmission cannot be guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore does not accept liability for any errors or omissions in the contents of this message, which arise as a result of e-mail transmission. If verification is required please request a hard-copy version.
On 2/13/20 12:45 PM, Jason Ralph wrote:
@Adrian Klaver,
I was concerned with the 1.4 value of tbloat and wastedbytes value, then again the last autovacuum was at 2020-02-13 02:25:22.533372-05 and I took this snapshot at 3:44PMEST. So it may be ok, what do you think?
What is your concern, storage space or performance of queries?
If performance then an EXPLAIN ANALYZE on a query will help show whether
there is an issue or not.
current_database | schemaname | tablename | tbloat | wastedbytes | iname | ibloat | wastedibytes
notimportant | public | members | 1.4 | 3080314880 | members_cobrid | 0.2 | 0notimportant=# select * from pg_stat_user_tables where relname = 'members';
-[ RECORD 1 ]-------+------------------------------
relid | 2045245
schemaname | public
relname | members
seq_scan | 55065
seq_tup_read | 201069350222
idx_scan | 5349501175
idx_tup_fetch | 7201402647
n_tup_ins | 910616
n_tup_upd | 46730942
n_tup_del | 1
n_tup_hot_upd | 41845682
n_live_tup | 18262438
n_dead_tup | 14740
n_mod_since_analyze | 2476
last_vacuum | 2019-10-13 01:01:40.587534-04
last_autovacuum | 2020-02-13 02:25:22.533372-05
last_analyze | 2019-10-13 01:01:41.916929-04
last_autoanalyze | 2020-02-13 13:44:46.273096-05
vacuum_count | 15
autovacuum_count | 92
analyze_count | 15
autoanalyze_count | 243Jason Ralph
--
Adrian Klaver
adrian.klaver@aklaver.com
What is your concern, storage space or performance of queries?
If performance then an EXPLAIN ANALYZE on a query will help show whether there is an issue or not.
@Adrian Klaver I guess I am after both, I would like to squeeze the most performance out of my tables and installation as possible. Also I would like to save space wherever possible. I have received a *bloat* load of information in this thread, so thanks. 😊
@Michael Lewis thanks for the idea of pg_repack, this looks awesome and I cant wait to test it.
Jason Ralph
-----Original Message-----
From: Adrian Klaver <adrian.klaver@aklaver.com>
Sent: Thursday, February 13, 2020 6:21 PM
To: Jason Ralph <jralph@affinitysolutions.com>; Michael Lewis <mlewis@entrata.com>
Cc: pgsql-general@lists.postgresql.org
Subject: Re: pg_upgrade —link does it remove table bloat
On 2/13/20 12:45 PM, Jason Ralph wrote:
@Adrian Klaver,
I was concerned with the 1.4 value of tbloat and wastedbytes value, then again the last autovacuum was at 2020-02-13 02:25:22.533372-05 and I took this snapshot at 3:44PMEST. So it may be ok, what do you think?
What is your concern, storage space or performance of queries?
If performance then an EXPLAIN ANALYZE on a query will help show whether there is an issue or not.
current_database | schemaname | tablename | tbloat | wastedbytes | iname | ibloat | wastedibytes
notimportant | public | members | 1.4 | 3080314880 | members_cobrid | 0.2 | 0notimportant=# select * from pg_stat_user_tables where relname =
'members'; -[ RECORD 1 ]-------+------------------------------
relid | 2045245
schemaname | public
relname | members
seq_scan | 55065
seq_tup_read | 201069350222
idx_scan | 5349501175
idx_tup_fetch | 7201402647
n_tup_ins | 910616
n_tup_upd | 46730942
n_tup_del | 1
n_tup_hot_upd | 41845682
n_live_tup | 18262438
n_dead_tup | 14740
n_mod_since_analyze | 2476
last_vacuum | 2019-10-13 01:01:40.587534-04
last_autovacuum | 2020-02-13 02:25:22.533372-05
last_analyze | 2019-10-13 01:01:41.916929-04
last_autoanalyze | 2020-02-13 13:44:46.273096-05
vacuum_count | 15
autovacuum_count | 92
analyze_count | 15
autoanalyze_count | 243Jason Ralph
--
Adrian Klaver
adrian.klaver@aklaver.com
This message contains confidential information and is intended only for the individual named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately by e-mail if you have received this e-mail by mistake and delete this e-mail from your system. E-mail transmission cannot be guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore does not accept liability for any errors or omissions in the contents of this message, which arise as a result of e-mail transmission. If verification is required please request a hard-copy version.