On 11/29/2010 05:47 PM, Pierre C wrote:
realm_51=# vacuum analyze verbose drones;
INFO: vacuuming "public.drones"
INFO: scanned index "drones_pk" to remove 242235 row versions
DETAIL: CPU 0.02s/0.11u sec elapsed 0.28 sec.
INFO: "drones": removed 242235 row versions in 1952 pages
DETAIL: CPU 0.01s/0.02u sec elapsed 0.03 sec.
INFO: index "drones_pk" now contains 174068 row versions in 721 pages
DETAIL: 107716 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
As you can see your index contains 174068 active rows and 242235 dead
rows that probably should have been removed a long time ago by
autovacuum, but you seem to have it turned off. It does not take a long
time to vacuum this table (only 0.3 sec) so it is not a high cost, you
should enable autovacuum and let it do the job (note that this doesn't
stop you from manual vacuuming after big updates).
Yes, you're right. I was doing some testing and I neglected to enable
vacuuming after inserts. But what this shows is that table drones is
having dead rows, and that table does get updated a lot. However, I
don't have any performance problems here. The UPDATE takes no more than
10 seconds even if I update 50k (out of 150k) rows.
I disabled autovacuum because I got a lot of "WARNING: pgstat wait
timeout" and I could see the autovacuum job (pg_stat_activity) running
during the run of the plpgsql function that handles inserts.
I left the autovacuum off but I do VACUUM after each CSV insert.
good
0 index pages have been deleted, 0 are currently reusable.
CPU 0.38s/0.12u sec elapsed 16.56 sec.
INFO: "drones_history": found 0 removable, 16903164 nonremovable row
versions in 129866 out of 195180 pages
DETAIL: 0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
0 pages are entirely empty.
CPU 2.00s/1.42u sec elapsed 49.24 sec.
good
INFO: vacuuming "pg_toast.pg_toast_2695510"
INFO: index "pg_toast_2695510_index" now contains 0 row versions in 1
pages
DETAIL: 0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO: "pg_toast_2695510": found 0 removable, 0 nonremovable row
versions in 0 out of 0 pages
DETAIL: 0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
same as above, no toast
Yes. Just to make things clear, I never update/delete drones_history. I
just INSERT, and every now and then I'll be doing SELECTs.
realm_51=# select version();
version
---------------------------------------------------------------------------------------------
PostgreSQL 8.4.2 on i686-pc-linux-gnu, compiled by GCC gcc (Debian
4.3.2-1.1) 4.3.2, 32-bit
(1 row)
Mario
ok
Try this :
CLUSTER drones_pkey ON drones;
Then check if your slow query gets a bit faster. If it does, try :
ALTER TABLE drones SET ( fillfactor = 50 );
ALTER INDEX drones_pkey SET ( fillfactor = 50 );
CLUSTER drones_pkey ON drones; (again)
This will make the updates on this table less problematic. VACUUM it
after each mass update.
Is this going to make any difference considering slow insert on
drones_history? Because INSERTs/UPDATEs on drones tables are fast. The
only noticable difference is that drones is 150k rows 'large' and
drones_history has around 25M rows:
realm_51=# select count(*) from drones_history ;
count
----------
25550475
(1 row)
Mario
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