Thread: Worsening performance with 7.4 on flash-based system
We are experiencing gradually worsening performance in PostgreSQL 7.4.7, on a system with the following specs: Linux OS (Fedora Core 1, 2.4 kernal) Flash file system (2 Gig, about 80% full) 256 Meg RAM 566 MHz Celeron CPU We use Orbit 2.9.8 to access PostGres. The database contains 62 tables. When the system is running with a fresh copy of the database, performance is fine. At its worst, we are seeing fairly simple SELECT queries taking up to 1 second to execute. When these queries are run in a loop, the loop can take up to 30 seconds to execute, instead of the 2 seconds or so that we would expect. VACUUM FULL ANALYZE helps, but doesn't seem to eliminate the problem. The following table show average execution time in "bad" performance mode in the first column, execution time after VACUUM ANALYZE in the second column, and % improvement (or degradation?) in the third. The fourth column show the query that was executed. 741.831|582.038|-21.5| ^IDECLARE table_cursor 170.065|73.032|-57.1| FETCH ALL in table_cursor 41.953|45.513|8.5| CLOSE table_cursor 61.504|47.374|-23.0| SELECT last_value FROM pm_id_seq 39.651|46.454|17.2| select id from la_looprunner 1202.170|265.316|-77.9| select id from rt_tran 700.669|660.746|-5.7| ^IDECLARE my_tran_load_cursor 1192.182|47.258|-96.0| FETCH ALL in my_tran_load_cursor 181.934|89.752|-50.7| CLOSE my_tran_load_cursor 487.285|873.474|79.3| ^IDECLARE my_get_router_cursor 51.543|69.950|35.7| FETCH ALL in my_get_router_cursor 48.312|74.061|53.3| CLOSE my_get_router_cursor 814.051|1016.219|24.8| SELECT $1 = 'INSERT' 57.452|78.863|37.3| select id from op_sched 48.010|117.409|144.6| select short_name, long_name from la_loopapp 54.425|58.352|7.2| select id from cd_range 45.289|52.330|15.5| SELECT last_value FROM rt_tran_id_seq 39.658|82.949|109.2| SELECT last_value FROM op_sched_id_seq 42.158|68.189|61.7| select card_id,router_id from rt_valid Has anyone else seen gradual performance degradation like this? Would upgrading to Postgres 8 help? Any other thoughts on directions for troubleshooting this? Thanks...
Well, since I got no response at all to this message, I can only assume that I've asked the question in an insufficient way, or else that no one has anything to offer on our problem. This was my first post to the list, so if there's a better way I should be asking this, or different data I should provide, hopefully someone will let me know... Thanks, Greg "Greg Stumph" <gregstumph@comcast.net> wrote in message news:e2b80f$245o$1@news.hub.org... > We are experiencing gradually worsening performance in PostgreSQL 7.4.7, > on a system with the following specs: > Linux OS (Fedora Core 1, 2.4 kernal) > Flash file system (2 Gig, about 80% full) > 256 Meg RAM > 566 MHz Celeron CPU > > We use Orbit 2.9.8 to access PostGres. The database contains 62 tables. > > When the system is running with a fresh copy of the database, performance > is fine. At its worst, we are seeing fairly simple SELECT queries taking > up to 1 second to execute. When these queries are run in a loop, the loop > can take up to 30 seconds to execute, instead of the 2 seconds or so that > we would expect. > > VACUUM FULL ANALYZE helps, but doesn't seem to eliminate the problem. > > The following table show average execution time in "bad" performance mode > in the first column, execution time after VACUUM ANALYZE in the second > column, and % improvement (or degradation?) in the third. The fourth > column show the query that was executed. > > 741.831|582.038|-21.5| ^IDECLARE table_cursor > 170.065|73.032|-57.1| FETCH ALL in table_cursor > 41.953|45.513|8.5| CLOSE table_cursor > 61.504|47.374|-23.0| SELECT last_value FROM pm_id_seq > 39.651|46.454|17.2| select id from la_looprunner > 1202.170|265.316|-77.9| select id from rt_tran > 700.669|660.746|-5.7| ^IDECLARE my_tran_load_cursor > 1192.182|47.258|-96.0| FETCH ALL in my_tran_load_cursor > 181.934|89.752|-50.7| CLOSE my_tran_load_cursor > 487.285|873.474|79.3| ^IDECLARE my_get_router_cursor > 51.543|69.950|35.7| FETCH ALL in my_get_router_cursor > 48.312|74.061|53.3| CLOSE my_get_router_cursor > 814.051|1016.219|24.8| SELECT $1 = 'INSERT' > 57.452|78.863|37.3| select id from op_sched > 48.010|117.409|144.6| select short_name, long_name from la_loopapp > 54.425|58.352|7.2| select id from cd_range > 45.289|52.330|15.5| SELECT last_value FROM rt_tran_id_seq > 39.658|82.949|109.2| SELECT last_value FROM op_sched_id_seq > 42.158|68.189|61.7| select card_id,router_id from rt_valid > > > Has anyone else seen gradual performance degradation like this? Would > upgrading to Postgres 8 help? Any other thoughts on directions for > troubleshooting this? > > Thanks... >
Usually when simple queries take a long time to run, it's the system tables (pg_*) that have become bloated and need vacuuming. But that's just random guess on my part w/o my detailed info. Greg Stumph wrote: > Well, since I got no response at all to this message, I can only assume that > I've asked the question in an insufficient way, or else that no one has > anything to offer on our problem. > > This was my first post to the list, so if there's a better way I should be > asking this, or different data I should provide, hopefully someone will let > me know... > > Thanks, > Greg > > "Greg Stumph" <gregstumph@comcast.net> wrote in message > news:e2b80f$245o$1@news.hub.org... >> We are experiencing gradually worsening performance in PostgreSQL 7.4.7, >> on a system with the following specs: >> Linux OS (Fedora Core 1, 2.4 kernal) >> Flash file system (2 Gig, about 80% full) >> 256 Meg RAM >> 566 MHz Celeron CPU >> >> We use Orbit 2.9.8 to access PostGres. The database contains 62 tables. >> >> When the system is running with a fresh copy of the database, performance >> is fine. At its worst, we are seeing fairly simple SELECT queries taking >> up to 1 second to execute. When these queries are run in a loop, the loop >> can take up to 30 seconds to execute, instead of the 2 seconds or so that >> we would expect. >> >> VACUUM FULL ANALYZE helps, but doesn't seem to eliminate the problem. >> >> The following table show average execution time in "bad" performance mode >> in the first column, execution time after VACUUM ANALYZE in the second >> column, and % improvement (or degradation?) in the third. The fourth >> column show the query that was executed. >> >> 741.831|582.038|-21.5| ^IDECLARE table_cursor >> 170.065|73.032|-57.1| FETCH ALL in table_cursor >> 41.953|45.513|8.5| CLOSE table_cursor >> 61.504|47.374|-23.0| SELECT last_value FROM pm_id_seq >> 39.651|46.454|17.2| select id from la_looprunner >> 1202.170|265.316|-77.9| select id from rt_tran >> 700.669|660.746|-5.7| ^IDECLARE my_tran_load_cursor >> 1192.182|47.258|-96.0| FETCH ALL in my_tran_load_cursor >> 181.934|89.752|-50.7| CLOSE my_tran_load_cursor >> 487.285|873.474|79.3| ^IDECLARE my_get_router_cursor >> 51.543|69.950|35.7| FETCH ALL in my_get_router_cursor >> 48.312|74.061|53.3| CLOSE my_get_router_cursor >> 814.051|1016.219|24.8| SELECT $1 = 'INSERT' >> 57.452|78.863|37.3| select id from op_sched >> 48.010|117.409|144.6| select short_name, long_name from la_loopapp >> 54.425|58.352|7.2| select id from cd_range >> 45.289|52.330|15.5| SELECT last_value FROM rt_tran_id_seq >> 39.658|82.949|109.2| SELECT last_value FROM op_sched_id_seq >> 42.158|68.189|61.7| select card_id,router_id from rt_valid >> >> >> Has anyone else seen gradual performance degradation like this? Would >> upgrading to Postgres 8 help? Any other thoughts on directions for >> troubleshooting this? >> >> Thanks... >> > >
On 4/29/06, Greg Stumph <gregstumph@comcast.net> wrote: > Well, since I got no response at all to this message, I can only assume that > I've asked the question in an insufficient way, or else that no one has > anything to offer on our problem. > > This was my first post to the list, so if there's a better way I should be > asking this, or different data I should provide, hopefully someone will let > me know... > > Thanks, > Greg > > "Greg Stumph" <gregstumph@comcast.net> wrote in message > news:e2b80f$245o$1@news.hub.org... > > We are experiencing gradually worsening performance in PostgreSQL 7.4.7, > > on a system with the following specs: > > Linux OS (Fedora Core 1, 2.4 kernal) > > Flash file system (2 Gig, about 80% full) > > 256 Meg RAM > > 566 MHz Celeron CPU > > > > We use Orbit 2.9.8 to access PostGres. The database contains 62 tables. > > > > When the system is running with a fresh copy of the database, performance > > is fine. At its worst, we are seeing fairly simple SELECT queries taking > > up to 1 second to execute. When these queries are run in a loop, the loop > > can take up to 30 seconds to execute, instead of the 2 seconds or so that > > we would expect. If you're inserting/updating/deleting a table or tables heavily, then you'll need to vacuum it a lot more often than a reasonably static table. Are you running contrib/autovacuum at all? PG 8.0 and above have autovacuum built in but 7.4.x needs to run the contrib version. PS - the latest 7.4 version is .12 - see http://www.postgresql.org/docs/7.4/interactive/release.html for what has changed (won't be much in performance terms but may fix data-loss bugs). -- Postgresql & php tutorials http://www.designmagick.com/
On Fri, 2006-04-28 at 13:36, Greg Stumph wrote: > Well, since I got no response at all to this message, I can only assume that > I've asked the question in an insufficient way, or else that no one has > anything to offer on our problem. > > This was my first post to the list, so if there's a better way I should be > asking this, or different data I should provide, hopefully someone will let > me know... I'd pick one particular case and do explain analyze on it both right after a reload, after running for a while, and after a vacuum analyze. Also, do a vacuum verbose on the database and post the output of that when the system's slowed down. Do you make a lot of temp tables? Run a lot of DDL? I don't think we have enough information to make a real informed decision, but I'm not sure what questions to ask to find out where the bottleneck is... Also, this could be the flash controller / card combo causing problems. Do you start with a freshly formatted card at the beginning? I know that flash controllers randomize the part of the card that gets written to so that you don't kill one part of it early due to writing on just on part. Could be that as the controller maps the card behind the scenes, the access gets slower on the lower level, and there's nothing PostgreSQL can do about it. Can you tell us what your usage patterns are in a bit more detail?