Problem with the sequence

sid tow wrote:

HI

I have a problem locating the documentation for "sequence". I want to get the detailed information about the columns present in a sequence table ie when I do

psql=# select * from foo_seq;
sequence_name | last_value | increment_by | max_value | min_value | cache_value | log_cnt | is_cycled | is_called
---------------------------+------------+--------------+---------------------+-----------+-------------+---------+-----------+-----------
foo_seq | 11 | 1 | 9223372036854775807 | 1 | 1 | 0 | f | t
(1 row)

I need to know where do i find documentation to know what the columns specify and I have already checked the man pages of create_sequence where I did not find much.
Can somebody give me ref to a link where I get such information.

From psql:
\d foo_seq
Sequence "public.foo_seq"
Column | Type
---------------+---------
sequence_name | name
last_value | bigint
increment_by | bigint
max_value | bigint
min_value | bigint
cache_value | bigint
log_cnt | bigint
is_cycled | boolean
is_called | boolean

From the manuals:
CREATE [ TEMPORARY | TEMP ] SEQUENCE name [ INCREMENT [ BY ] increment ]
[ MINVALUE minvalue | NO MINVALUE ] [ MAXVALUE maxvalue | NO MAXVALUE ]
[ START [ WITH ] start ] [ CACHE cache ] [ [ NO ] CYCLE ]

For the ones not mentioned in the manual:
last_value - is the last value given out by the sequence
is_called - says whether nextval() has been called in this session
(and so whether it is safe to call currval())
log_cnt - don't know, googling suggests it's to do with WAL logging.

Does that help?
--
Richard Huxton
Archonet Ltd

I wrote a very basic entry about this at improveyourweb some weeks ago
(http://www.improveyourweb.com/?q=node/2). Hope it helps.

In the source code, sequence.c, you can read something like:

/*
* Decide whether we should emit a WAL log record. If so, force up
* the fetch count to grab SEQ_LOG_VALS more values than we actually
* need to cache. (These will then be usable without logging.)
*
* If this is the first nextval after a checkpoint, we must force a new
* WAL record to be written anyway, else replay starting from the
* checkpoint would fail to advance the sequence past the logged
* values. In this case we may as well fetch extra values.
*/
if (log < fetch)...

log is log_cnt (or log_cnt-1 if is_called equals false)
fetch is cache_value (or cache_value-1 if is_called equals false)

If someone more can help, it would interesting for all understand this better.

Thanks that should help but what about the rest of the columns can u explain what is "is_cycled" and "cache_value". Thanks in advance.

Richard Huxton <dev@archonet.com> wrote:sid tow wrote:

HI

I have a problem locating the documentation for "sequence". I want to get the detailed information about the columns present in a sequence table ie when I do

psql=# select * from foo_seq;
sequence_name | last_value | increment_by | max_value | min_value | cache_value | log_cnt | is_cycled | is_called
---------------------------+------------+--------------+---------------------+-----------+-------------+---------+-----------+-----------
foo_seq | 11 | 1 | 9223372036854775807 | 1 | 1 | 0 | f | t
(1 row)

I need to know where do i find documentation to know what the columns specify and I have already checked the man pages of create_sequence where I did not find much.
Can somebody give me ref to a link where I get such information.

From psql:
\d foo_seq
Sequence "public.foo_seq"
Column | Type
---------------+---------
sequence_name | name
last_value | bigint
increment_by | bigint
max_value | bigint
min_value | bigint
cache_value | bigint
log_cnt | bigint
is_cycled | boolean
is_called | boolean

From the manuals:
CREATE [ TEMPORARY | TEMP ] SEQUENCE name [ INCREMENT [ BY ] increment ]
[ MINVALUE minvalue | NO MINVALUE ] [ MAXVALUE maxvalue | NO MAXVALUE ]
[ START [ WITH ] start ] [ CACHE cache ] [ [ NO ] CYCLE ]

For the ones not mentioned in the manual:
last_value - is the last value given out by the sequence
is_called - says whether nextval() has been called in this session
(and so whether it is safe to call currval())
log_cnt - don't know, googling suggests it's to do with WAL logging.

Does that help?
--
Richard Huxton
Archonet Ltd

---------------------------------
Do you Yahoo!?
Yahoo! Search presents - Jib Jab's 'Second Term'

sid tow wrote:

Thanks that should help but what about the rest of the columns can u
explain what is "is_cycled" and "cache_value". Thanks in advance.

See the manuals. Section "SQL Commands", "CREATE SEQUENCE"

--
Richard Huxton
Archonet Ltd

Thanks that should help but what about the rest of the columns can u explain what is "is_cycled" and "cache_value". Thanks in advance.

Richard Huxton <dev@archonet.com> wrote: sid tow wrote:

HI

I have a problem locating the documentation for "sequence". I want to get the detailed information about the columns present in a sequence table ie when I do

psql=# select * from foo_seq;
sequence_name | last_value | increment_by | max_value | min_value | cache_value | log_cnt | is_cycled | is_called
---------------------------+------------+--------------+---------------------+-----------+-------------+---------+-----------+-----------
foo_seq | 11 | 1 | 9223372036854775807 | 1 | 1 | 0 | f | t
(1 row)

I need to know where do i find documentation to know what the columns specify and I have already checked the man pages of create_sequence where I did not find much.
Can somebody give me ref to a link where I get such information.

From psql:
\d foo_seq
Sequence "public.foo_seq"
Column | Type
---------------+---------
sequence_name | name
last_value | bigint
increment_by | bigint
max_value | bigint
min_value | bigint
cache_value | bigint
log_cnt | bigint
is_cycled | boolean
is_called | boolean

From the manuals:
CREATE [ TEMPORARY | TEMP ] SEQUENCE name [ INCREMENT [ BY ] increment ]
[ MINVALUE minvalue | NO MINVALUE ] [ MAXVALUE maxvalue | NO MAXVALUE ]
[ START [ WITH ] start ] [ CACHE cache ] [ [ NO ] CYCLE ]

For the ones not mentioned in the manual:
last_value - is the last value given out by the sequence
is_called - says whether nextval() has been called in this session
(and so whether it is safe to call currval())
log_cnt - don't know, googling suggests it's to do with WAL logging.

Does that help?
--
Richard Huxton
Archonet Ltd

---------------------------------
Do you Yahoo!?
Yahoo! Search presents - Jib Jab's 'Second Term'

---------------------------------
Do you Yahoo!?
Yahoo! Search presents - Jib Jab's 'Second Term'