Re: Prepared statements generating a lot of temp files.

thanks will check this.

is there some formula you are using to arrive at this number for work_mem?

we have queries that frequently have more than a dozen joins/aggregates. so have been conservative in changing work_mem...

btw, using pg version 10, (i know its old and am trying to convince folks to upgrade :)

thanks

karthik

---- On Thu, 23 Mar 2023 15:56:36 +0530 MichaelDBA <mailto:MichaelDBA(at)sqlexec(dot)com> wrote ---

Looks like you can handle 256MB work_mem. 
Give it a shot and monitor temp_files.  You do have log_temp_files = 0,
right?  Also, keep an eye out for "out of memory" log file errors.  What
PG version are you using?

Karthik Krishnakumar wrote on 3/23/2023 6:21 AM:

Regards,

Michael Vitale

mailto:michaelvitale(at)sqlexec(dot)com

703-600-9343

 

RAM -
256GB

shared_buffers - 64GB

maintenance_work_mem
- 1GB

work_mem - 24MB

there are ~50 active
connections at any given time.

from
pg_badger - average temp file size for bulk insert/update is about
200MB, max size is multiple GB's depending on the table.

it
is a write heavy workload - with inserts/updates happening around the
clock.

thanks

karthik

----
On Thu, 23 Mar 2023 15:33:11 +0530 MichaelDBA <mailto:MichaelDBA(at)sqlexec(dot)com> wrote ---

Perhaps
take the other approach: increase
work_mem to make the bulk inserts fit into memory.  You can easily undo
work_mem changes.  It only requires a sighup: reload, not restart.

What
memory do you have now and what is work_mem currently set to? 
Also, have many concurrent, active connections do you average at a time?

Regards,

Michael
Vitale

Karthik
Krishnakumar wrote on 3/23/2023 5:59 AM:

Regards,

Michael Vitale

mailto:michaelvitale(at)sqlexec(dot)com

703-600-9343

 

thanks - checked with the devs and
it does look like the application is doing some sort of a bulk insert,
and at the moment it cannot be changed to use "COPY FROM".

will
limiting bulk inserts to match the work_mem(assuming this is the guc
that is used in this case) reduce this disk activity?

thanks,

karthik

----
On Thu, 23 Mar 2023 14:43:19 +0530 mailto:Michaeldba(at)sqlexec(dot)com wrote ---

Look at
the size of the bind variables and also whether you are doing bulk
inserts

Sent from my iPad

On Mar 23, 2023, at 5:10 AM,
Karthik Krishnakumar <mailto:karthikk(at)zohocorp(dot)com>
wrote:



Hi admins,

I
am analyzing temp files being generated using pg_badger.

Under
"queries generating the most temporary files", I am finding
insert/update queries (via prepared statements) writing a lot of data to
temp files.

I am trying to figure why inserts are
generating such temp files.

Why are inserts/updates
generating temp files?

what can be done to avoid this ?

thanks,

karthik