Обсуждение: Sub-optimal plan for a paginated query on a view with another view inside of it.
Good day, I have a performance issue when JOINing a view within another view more than once. The query takes over three seconds to execute, which is too long in this case. It's not a problem if the tables are nearlyempty, but that isn't the case on the production database. I suspect the planner thinks it's better to first put together the v_address view and JOIN it to the parcel table later on,but the function "fx_get_user_tree_subordinates_by_id" should be JOINed to the parcel table first, as it reduces the numberof rows to less than 200 and any following JOINs would be much faster. I have also ran vacuum, reindex and analyze on the whole database, but it seems to have had to effect. Is there any way to nudge the planner toward that way of execution? This is the query: https://app.box.com/s/jzxiuuxoyj28q4q8rzxr This is the query plan: https://app.box.com/s/u8nk6qvkjs4ae7l7dh4h (plain text) https://app.box.com/s/jzxiuuxoyj28q4q8rzxr (graphical output) These are the views: https://app.box.com/s/uibzidsazwv3eeauovuk (paginated view) https://app.box.com/s/v71vyexmdyl97m4f3m6u (used three times in the paginated view). Thank you. Peter Slapansky
I apologise, I have neglected to mention Postgres versions tested. It occurs with 9.0 and 9.2
I have typo in my previous message - the sentence about vacuum, reindex and analyze should be:
"I had also run vacuum, reindex and analyze on the whole database, but it seems to have had no effect."
Thanks for any thoughts on the issue.
Peter Slapansky
______________________________________________________________
> Od: <slapo@centrum.sk>
> Komu: <pgsql-performance@postgresql.org>
> Dátum: 02.08.2013 15:43
> Predmet: Sub-optimal plan for a paginated query on a view with another view inside of it.
>
Good day,
I have a performance issue when JOINing a view within another view more than once.
The query takes over three seconds to execute, which is too long in this case. It's not a problem if the tables are nearly empty, but that isn't the case on the production database.
I suspect the planner thinks it's better to first put together the v_address view and JOIN it to the parcel table later on, but the function "fx_get_user_tree_subordinates_by_id" should be JOINed to the parcel table first, as it reduces the number of rows to less than 200 and any following JOINs would be much faster.
I have also ran vacuum, reindex and analyze on the whole database, but it seems to have had to effect.
Is there any way to nudge the planner toward that way of execution?
This is the query:
https://app.box.com/s/jzxiuuxoyj28q4q8rzxr
This is the query plan:
https://app.box.com/s/u8nk6qvkjs4ae7l7dh4h (plain text)
https://app.box.com/s/jzxiuuxoyj28q4q8rzxr (graphical output)
These are the views:
https://app.box.com/s/uibzidsazwv3eeauovuk (paginated view)
https://app.box.com/s/v71vyexmdyl97m4f3m6u (used three times in the paginated view).
Thank you.
Peter Slapansky
Re: Sub-optimal plan for a paginated query on a view with another view inside of it.
Hello please, send result of EXPLAIN ANALYZE please, use a http://explain.depesz.com/ for saving a plan there is a more than 8 joins - so try to set geqo_threshold to 16, join_collapse_limit to 16, and from_collapse_limit to 16. Regards Pavel Stehule 2013/8/2 <slapo@centrum.sk>: > Good day, > > I have a performance issue when JOINing a view within another view more than once. > The query takes over three seconds to execute, which is too long in this case. It's not a problem if the tables are nearlyempty, but that isn't the case on the production database. > > I suspect the planner thinks it's better to first put together the v_address view and JOIN it to the parcel table lateron, but the function "fx_get_user_tree_subordinates_by_id" should be JOINed to the parcel table first, as it reducesthe number of rows to less than 200 and any following JOINs would be much faster. > > I have also ran vacuum, reindex and analyze on the whole database, but it seems to have had to effect. > > Is there any way to nudge the planner toward that way of execution? > > This is the query: > https://app.box.com/s/jzxiuuxoyj28q4q8rzxr > > This is the query plan: > https://app.box.com/s/u8nk6qvkjs4ae7l7dh4h (plain text) > https://app.box.com/s/jzxiuuxoyj28q4q8rzxr (graphical output) > > These are the views: > https://app.box.com/s/uibzidsazwv3eeauovuk (paginated view) > https://app.box.com/s/v71vyexmdyl97m4f3m6u (used three times in the paginated view). > > > Thank you. > > Peter Slapansky > > > -- > Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance
Good day,
I have included a link to the result of EXPLAIN ANALYZE. It's this one:
https://app.box.com/s/u8nk6qvkjs4ae7l7dh4h
Here's a link to Depesz's explain (if links to the site are okay):
http://explain.depesz.com/s/gCk
I have just tried setting geqo_threshold, join_collapse_limit and from_collapse_limit to 16, but it yielded no improvement.
Changing those three parameters to 32 did speed up the query from about 3.3 seconds to about a second (give or take 50 ms), which is a pretty good improvement, but not quite there, as I'm looking to bring it down to about 300 ms if possible. Changing those three settings to 48 yielded no improvements over 32.
Is there possibly something something else to tweak there?
Here's EXPLAIN ANALYZE output when the three settings have been set to 32:
http://explain.depesz.com/s/cj2
Thank you.
Peter Slapansky
______________________________________________________________
> Od: Pavel Stehule <pavel.stehule@gmail.com>
> Komu: <slapo@centrum.sk>
> Dátum: 06.08.2013 21:01
> Predmet: Re: [PERFORM] Sub-optimal plan for a paginated query on a view with another view inside of it.
>
> CC: pgsql-performance@postgresql.org
Hello
please, send result of EXPLAIN ANALYZE
please, use a http://explain.depesz.com/ for saving a plan
there is a more than 8 joins - so try to set geqo_threshold to 16,
join_collapse_limit to 16, and from_collapse_limit to 16.
Regards
Pavel Stehule
2013/8/2 <slapo@centrum.sk>:
> Good day,
>
> I have a performance issue when JOINing a view within another view more than once.
> The query takes over three seconds to execute, which is too long in this case. It's not a problem if the tables are nearly empty, but that isn't the case on the production database.
>
> I suspect the planner thinks it's better to first put together the v_address view and JOIN it to the parcel table later on, but the function "fx_get_user_tree_subordinates_by_id" should be JOINed to the parcel table first, as it reduces the number of rows to less than 200 and any following JOINs would be much faster.
>
> I have also ran vacuum, reindex and analyze on the whole database, but it seems to have had to effect.
>
> Is there any way to nudge the planner toward that way of execution?
>
> This is the query:
> https://app.box.com/s/jzxiuuxoyj28q4q8rzxr
>
> This is the query plan:
> https://app.box.com/s/u8nk6qvkjs4ae7l7dh4h (plain text)
> https://app.box.com/s/jzxiuuxoyj28q4q8rzxr (graphical output)
>
> These are the views:
> https://app.box.com/s/uibzidsazwv3eeauovuk (paginated view)
> https://app.box.com/s/v71vyexmdyl97m4f3m6u (used three times in the paginated view).
>
>
> Thank you.
>
> Peter Slapansky
>
>
> --
> Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-performance
From: pgsql-performance-owner@postgresql.org [mailto:pgsql-performance-owner@postgresql.org] On Behalf Of slapo@centrum.sk Sent: Wednesday, August 07, 2013 8:43 AM To: Pavel Stehule Cc: pgsql-performance@postgresql.org Subject: [PERFORM] Re: [PERFORM] Sub-optimal plan for a paginated query on a view with another view inside of it. Good day, I have included a link to the result of EXPLAIN ANALYZE. It's this one: https://app.box.com/s/u8nk6qvkjs4ae7l7dh4h Here's a link to Depesz's explain (if links to the site are okay): http://explain.depesz.com/s/gCk I have just tried setting geqo_threshold, join_collapse_limit and from_collapse_limit to 16, but it yielded no improvement. Changing those three parameters to 32 did speed up the query from about 3.3 seconds to about a second (give or take 50 ms),which is a pretty good improvement, but not quite there, as I'm looking to bring it down to about 300 ms if possible.Changing those three settings to 48 yielded no improvements over 32. Is there possibly something something else to tweak there? Here's EXPLAIN ANALYZE output when the three settings have been set to 32: http://explain.depesz.com/s/cj2 Thank you. Peter Slapansky ----- Your last explain analyze (with 3 settings set to 32) shows query duration 10ms, not 1sec. Am I wrong? Regards, Igor Neyman
You're right, it does... but it's quite odd, because I re-ran the explain-analyze statement and got the same results.
Still, the query now runs for about a second as mentioned before, so it's almost like something's missing from the explain, but I'm certain I copied it all.
I did this via pgadmin, but that shouldn't matter, should it?
Thank you,
Peter Slapansky
______________________________________________________________
> Od: Igor Neyman <ineyman@perceptron.com>
> Komu: "slapo@centrum.sk" <slapo@centrum.sk>, Pavel Stehule <pavel.stehule@gmail.com>
> Dátum: 07.08.2013 15:47
> Predmet: RE: [PERFORM] Re: [PERFORM] Sub-optimal plan for a paginated query on a view with another view inside of it.
>
> CC: "pgsql-performance@postgresql.org"
Your last explain analyze (with 3 settings set to 32) shows query duration 10ms, not 1sec.
Am I wrong?
Regards,
Igor Neyman
______________________________________________________________
From: pgsql-performance-owner@postgresql.org [mailto:pgsql-performance-owner@postgresql.org] On Behalf Of slapo@centrum.sk
Sent: Wednesday, August 07, 2013 8:43 AM
To: Pavel Stehule
Cc: pgsql-performance@postgresql.org
Subject: [PERFORM] Re: [PERFORM] Sub-optimal plan for a paginated query on a view with another view inside of it.
Good day,
I have included a link to the result of EXPLAIN ANALYZE. It's this one:
https://app.box.com/s/u8nk6qvkjs4ae7l7dh4h
Here's a link to Depesz's explain (if links to the site are okay):
http://explain.depesz.com/s/gCk
I have just tried setting geqo_threshold, join_collapse_limit and from_collapse_limit to 16, but it yielded no improvement.
Changing those three parameters to 32 did speed up the query from about 3.3 seconds to about a second (give or take 50 ms), which is a pretty good improvement, but not quite there, as I'm looking to bring it down to about 300 ms if possible. Changing those three settings to 48 yielded no improvements over 32.
Is there possibly something something else to tweak there?
Here's EXPLAIN ANALYZE output when the three settings have been set to 32:
http://explain.depesz.com/s/cj2
Thank you.
Peter Slapansky
From: slapo@centrum.sk [mailto:slapo@centrum.sk] Sent: Wednesday, August 07, 2013 10:43 AM To: Igor Neyman; Pavel Stehule Cc: pgsql-performance@postgresql.org Subject: RE: [PERFORM] Re: [PERFORM] Sub-optimal plan for a paginated query on a view with another view inside of it. You're right, it does... but it's quite odd, because I re-ran the explain-analyze statement and got the same results. Still, the query now runs for about a second as mentioned before, so it's almost like something's missing from the explain,but I'm certain I copied it all. I did this via pgadmin, but that shouldn't matter, should it? Thank you, Peter Slapansky ______________________________________________________________ _________________________________________________________ At very end of explain analyze output there should be a line: Total runtime: .... What do you get there? Regards, Igor Neyman
2013/8/7 Igor Neyman <ineyman@perceptron.com>: > > > From: pgsql-performance-owner@postgresql.org [mailto:pgsql-performance-owner@postgresql.org] On Behalf Of slapo@centrum.sk > Sent: Wednesday, August 07, 2013 8:43 AM > To: Pavel Stehule > Cc: pgsql-performance@postgresql.org > Subject: [PERFORM] Re: [PERFORM] Sub-optimal plan for a paginated query on a view with another view inside of it. > > Good day, > > I have included a link to the result of EXPLAIN ANALYZE. It's this one: > https://app.box.com/s/u8nk6qvkjs4ae7l7dh4h > > Here's a link to Depesz's explain (if links to the site are okay): > http://explain.depesz.com/s/gCk > > I have just tried setting geqo_threshold, join_collapse_limit and from_collapse_limit to 16, but it yielded no improvement. > Changing those three parameters to 32 did speed up the query from about 3.3 seconds to about a second (give or take 50ms), which is a pretty good improvement, but not quite there, as I'm looking to bring it down to about 300 ms if possible.Changing those three settings to 48 yielded no improvements over 32. > Is there possibly something something else to tweak there? > > Here's EXPLAIN ANALYZE output when the three settings have been set to 32: > http://explain.depesz.com/s/cj2 > > Thank you. > > Peter Slapansky > > ----- > > Your last explain analyze (with 3 settings set to 32) shows query duration 10ms, not 1sec. > Am I wrong? I afraid so 1 sec is planning time :( .. So execution is fast, but planning is expensive and relatively slow .. maybe prepared statements can helps in this case. Regards Pavel > > Regards, > Igor Neyman >
2013/8/7 <slapo@centrum.sk>: > You're right, it does... but it's quite odd, because I re-ran the > explain-analyze statement and got the same results. > > Still, the query now runs for about a second as mentioned before, so it's > almost like something's missing from the explain, but I'm certain I copied > it all. what is time of EXPLAIN only ? Pavel > > > > I did this via pgadmin, but that shouldn't matter, should it? > > > > Thank you, > > > > Peter Slapansky > > ______________________________________________________________ >> Od: Igor Neyman <ineyman@perceptron.com> >> Komu: "slapo@centrum.sk" <slapo@centrum.sk>, Pavel Stehule >> <pavel.stehule@gmail.com> >> Dátum: 07.08.2013 15:47 >> Predmet: RE: [PERFORM] Re: [PERFORM] Sub-optimal plan for a paginated >> query on a view with another view inside of it. >> > >> CC: "pgsql-performance@postgresql.org" > > Your last explain analyze (with 3 settings set to 32) shows query duration > 10ms, not 1sec. > Am I wrong? > > Regards, > Igor Neyman > > > > ______________________________________________________________ > > > From: pgsql-performance-owner@postgresql.org > [mailto:pgsql-performance-owner@postgresql.org] On Behalf Of > slapo@centrum.sk > Sent: Wednesday, August 07, 2013 8:43 AM > To: Pavel Stehule > Cc: pgsql-performance@postgresql.org > Subject: [PERFORM] Re: [PERFORM] Sub-optimal plan for a paginated query on a > view with another view inside of it. > > Good day, > > I have included a link to the result of EXPLAIN ANALYZE. It's this one: > https://app.box.com/s/u8nk6qvkjs4ae7l7dh4h > > Here's a link to Depesz's explain (if links to the site are okay): > http://explain.depesz.com/s/gCk > > I have just tried setting geqo_threshold, join_collapse_limit and > from_collapse_limit to 16, but it yielded no improvement. > Changing those three parameters to 32 did speed up the query from about 3.3 > seconds to about a second (give or take 50 ms), which is a pretty good > improvement, but not quite there, as I'm looking to bring it down to about > 300 ms if possible. Changing those three settings to 48 yielded no > improvements over 32. > Is there possibly something something else to tweak there? > > Here's EXPLAIN ANALYZE output when the three settings have been set to 32: > http://explain.depesz.com/s/cj2 > > Thank you. > > Peter Slapansky >
I got:
"Total runtime: 9.313 ms" in pgAdmin
"Total runtime: 9.363 ms" in psql.
But timing after the query finished was 912.842 ms in psql.
Cheers,
Peter Slapansky
______________________________________________________________
> Od: Igor Neyman <ineyman@perceptron.com>
> Komu: "slapo@centrum.sk" <slapo@centrum.sk>, Pavel Stehule <pavel.stehule@gmail.com>
> Dátum: 07.08.2013 16:48
> Predmet: RE: [PERFORM] Re: [PERFORM] Sub-optimal plan for a paginated query on a view with another view inside of it.
>
> CC: "pgsql-performance@postgresql.org"
From: slapo@centrum.sk [mailto:slapo@centrum.sk]
Sent: Wednesday, August 07, 2013 10:43 AM
To: Igor Neyman; Pavel Stehule
Cc: pgsql-performance@postgresql.org
Subject: RE: [PERFORM] Re: [PERFORM] Sub-optimal plan for a paginated query on a view with another view inside of it.
You're right, it does... but it's quite odd, because I re-ran the explain-analyze statement and got the same results.
Still, the query now runs for about a second as mentioned before, so it's almost like something's missing from the explain, but I'm certain I copied it all.
I did this via pgadmin, but that shouldn't matter, should it?
Thank you,
Peter Slapansky
______________________________________________________________
_________________________________________________________
At very end of explain analyze output there should be a line:
Total runtime: ....
What do you get there?
Regards,
Igor Neyman
From: slapo@centrum.sk [mailto:slapo@centrum.sk] Sent: Wednesday, August 07, 2013 11:34 AM To: Igor Neyman; Pavel Stehule Cc: pgsql-performance@postgresql.org Subject: RE: [PERFORM] Re: [PERFORM] Sub-optimal plan for a paginated query on a view with another view inside of it. I got: "Total runtime: 9.313 ms" in pgAdmin "Total runtime: 9.363 ms" in psql. But timing after the query finished was 912.842 ms in psql. Cheers, Peter Slapansky ______________________________________________________________ That proves what Pavel suggested regarding planning time. Regards, Igor Neyman
<slapo@centrum.sk> writes:
> "Total runtime: 9.313 ms" in pgAdmin
> "Total runtime: 9.363 ms" in psql.
> But timing after the query finished was 912.842 ms in psql.
Well, that's the downside of increasing join_collapse_limit and
from_collapse_limit: you might get a better plan, but it takes a lot
longer to get it because the planner is considering many more options.
If you're sufficiently desperate, you could consider rewriting the query
so that its JOIN structure matches the join order that the planner chooses
at the high collapse_limit settings. Then you can reduce the limits back
down and it'll still find the same plan. This tends to suck from a query
readability/maintainability standpoint though :-(.
The prepared-query approach might offer a solution too, if the good plan
isn't dependent on specific parameter values.
regards, tom lane
I was afraid of something worse but hoping for something better in terms of maintainability. At least now I have a good explanation.:-) I just hope the embedded view use won't interfere too much. Thanks everyone. Regards, Peter Slapansky ______________________________________________________________ > Od: Tom Lane <tgl@sss.pgh.pa.us> > Komu: <slapo@centrum.sk> > Dátum: 07.08.2013 17:53 > Predmet: Re: [PERFORM] RE: [PERFORM] Re: [PERFORM] Sub-optimal plan for a paginated query on a view with another view insideof it. > > CC: "Igor Neyman", "Pavel Stehule", "pgsql-performance@postgresql.org" <slapo@centrum.sk> writes: > "Total runtime: 9.313 ms" in pgAdmin > "Total runtime: 9.363 ms" in psql. > But timing after the query finished was 912.842 ms in psql. Well, that's the downside of increasing join_collapse_limit and from_collapse_limit: you might get a better plan, but it takes a lot longer to get it because the planner is considering many more options. If you're sufficiently desperate, you could consider rewriting the query so that its JOIN structure matches the join order that the planner chooses at the high collapse_limit settings. Then you can reduce the limits back down and it'll still find the same plan. This tends to suck from a query readability/maintainability standpoint though :-(. The prepared-query approach might offer a solution too, if the good plan isn't dependent on specific parameter values. regards, tom lane