----- On 5 Apr, 2019, at 4:14 AM, Jeff Janes <jeff.ja...@gmail.com> wrote:
> On Thu, Apr 4, 2019 at 3:42 AM Duncan Kinnear < [ > mailto:duncan.kinn...@mccarthy.co.nz | duncan.kinn...@mccarthy.co.nz ] > > wrote: >> the EXPLAIN (ANALYSE, TIMING TRUE) of this query gives: >> Update on next_id (cost=0.14..8.16 rows=1 width=36) (actual time=0.057..0.057 >> rows=0 loops=1) >> -> Index Scan using next_id_pk on next_id (cost=0.14..8.16 rows=1 width=36) >> (actual time=0.039..0.040 rows=1 loops=1) >> Index Cond: ((id)::text = 'Session'::text) >> Planning Time: 0.083 ms >> Execution Time: 0.089 ms >> which is significantly less than 50ms. > The EXPLAIN ANALYZE doesn't include the time needed to fsync the transaction > logs. It measures only the update itself, not the implicit commit at the end. > DBeaver is seeing the fsync-inclusive time. 50ms is pretty long, but some file > systems and OSes seem to be pretty inefficient at this and take several disk > revolutions to get the data down. >> Now, if I point DBeaver to a VM server on the same gigabit network switch, >> running version: >> 9.5.3 on i386-pc-solaris2.11, compiled by cc: Sun C 5.10 SunOS_i386 Patch >> 142363-07 2010/12/09, 64-bit >> then the same query executes in about 2-3ms > That machine probably has hardware to do a fast fsync, has fsync turned off, > or > is lying about the safety of its data. Just a quick update. I tried performing a sequence of BEGIN; UPDATE ...; COMMIT; and I got the following log entries: Apr 10 09:02:40 duncanpc postgres[7656]: 2019-04-10 09:02:40.639 NZST [29887] LOG: duration: 0.025 ms parse <unnamed>: begin Apr 10 09:02:40 duncanpc postgres[7656]: 2019-04-10 09:02:40.639 NZST [29887] LOG: duration: 0.014 ms bind <unnamed>: begin Apr 10 09:02:40 duncanpc postgres[7656]: 2019-04-10 09:02:40.639 NZST [29887] LOG: duration: 0.003 ms execute <unnamed>: begin Apr 10 09:02:40 duncanpc postgres[7656]: 2019-04-10 09:02:40.639 NZST [29887] LOG: duration: 0.045 ms parse <unnamed>: update NEXT_ID set next_value=next_value+1 where id='Session' Apr 10 09:02:40 duncanpc postgres[7656]: 2019-04-10 09:02:40.640 NZST [29887] LOG: duration: 0.055 ms bind <unnamed>: update NEXT_ID set next_value=next_value+1 where id='Session' Apr 10 09:02:40 duncanpc postgres[7656]: 2019-04-10 09:02:40.640 NZST [29887] LOG: duration: 0.059 ms execute <unnamed>: update NEXT_ID set next_value=next_value+1 where id='Session' Apr 10 09:02:40 duncanpc postgres[7656]: 2019-04-10 09:02:40.640 NZST [29887] LOG: duration: 0.004 ms parse <unnamed>: commit Apr 10 09:02:40 duncanpc postgres[7656]: 2019-04-10 09:02:40.640 NZST [29887] LOG: duration: 0.003 ms bind <unnamed>: commit Apr 10 09:02:40 duncanpc postgres[7656]: 2019-04-10 09:02:40.690 NZST [29887] LOG: duration: 50.237 ms execute <unnamed>: commit So this confirms that the overhead is indeed happening in the COMMIT part. But how do I get more detailed logging to see what it is doing? Note, in a previous reply to Jeff (which I forgot to CC to the list) I explained that the slow machines are both using BTRFS as the filesystem, and a bit of googling has revealed that using PostgreSQL on BTRFS filesystems is (don't cross the streams) bad. Jeff, I will try adding the wait event stuff to see if that it what it is doing. Cheers, Duncan
