I've been searching for some information about Postgres 9.1 stats which are
stored in pg_stat_database - on the web and on IRC. I found SOME information
for 9.2 but even that doesn't seem to be accurate. What I'm after is to get
proper transaction stats ie commits and rollbacks. Also I've no clue what
tup_fetched and tup_returned mean.
I made a few tests on a dummy database. I created a database called statistics
and one simple table called films in it. Inserted a few values into it and here
is what I found out:
statistics=# select xact_commit, xact_rollback, blks_read,
blks_hit,tup_returned, tup_fetched, tup_inserted, tup_updated, tup_deleted from
pg_stat_database where datname='statistics';
xact_commit | xact_rollback | blks_read | blks_hit | tup_returned |
tup_fetched | tup_inserted | tup_updated | tup_deleted
-------------+---------------+-----------+----------+--------------+-------------+--------------+-------------+-------------
94 | 0 | 182 | 3259 | 18345 |
1293 | 27 | 0 | 0
(1 row)
statistics=# INSERT INTO films VALUES ('UA509', 'Bananas', 105, '1971-04-13',
'Comedy', '85 minutes');
INSERT 0 1
statistics=# select xact_commit, xact_rollback, blks_read,
blks_hit,tup_returned, tup_fetched, tup_inserted, tup_updated, tup_deleted from
pg_stat_database where datname='statistics';
xact_commit | xact_rollback | blks_read | blks_hit | tup_returned |
tup_fetched | tup_inserted | tup_updated | tup_deleted
-------------+---------------+-----------+----------+--------------+-------------+--------------+-------------+-------------
97 | 1 | 182 | 3261 | 18345 |
1293 | 28 | 0 | 0
(1 row)
statistics=# select * from films;
code | title | did | date_prod | kind | len
-------+----------+-----+------------+--------+----------
UA502 | Bananas | 105 | 1971-07-13 | Comedy | 01:22:00
UA503 | BanaAAas | 106 | 1971-07-13 | Comedy | 01:26:00
UA504 | BanaAAas | 106 | 1971-07-13 | Comedy | 01:26:00
UA509 | Bananas | 105 | 1971-04-13 | Comedy | 01:25:00
(4 rows)
statistics=# select xact_commit, xact_rollback, blks_read,
blks_hit,tup_returned, tup_fetched, tup_inserted, tup_updated, tup_deleted from
pg_stat_database where datname='statistics';
xact_commit | xact_rollback | blks_read | blks_hit | tup_returned |
tup_fetched | tup_inserted | tup_updated | tup_deleted
-------------+---------------+-----------+----------+--------------+-------------+--------------+-------------+-------------
99 | 1 | 182 | 3262 | 18349 |
1293 | 28 | 0 | 0
(1 row)
What this shows is that xact_commit increases by 3 after just one row insert.
tup_inserted does seem to report correct value. After simple SELECT,
xact_commit increases by 2 - kind of strange as SELECT shouldn't really be
increasing xact_commit ? What I'm trying to do is to gather some reasonable
data which would give me an idea about how many transactions/s particular
Database is doing. Could any of the gurus shed some light on this ? I take it
that tup_fetched and tup_returned are some really damn random values which only
Postgres developers understand :) Thanks in advance!
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