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. On Thu, 03 Feb 2005 09:22:55 +0000, Richard Huxton <dev@xxxxxxxxxxxx> 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 > > ---------------------------(end of broadcast)--------------------------- > TIP 8: explain analyze is your friend > ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org
