hmmm, I think spilling over to disk for temporary tables is handled by
an entirely different branch in the PG source code. In fact, some other
folks have chimed in and said log_temp_files doesn't relate to temp
files at all use by temporary tables, just queries as you mentioned
below elsewhere. This seems to be a dark area of PG that is not
convered well.
Regards,
Michael Vitale
Laurenz Albe wrote on 7/12/2021 8:01 AM:
On Thu, 2021-07-08 at 17:22 -0400, MichaelDBA wrote:
I got a question about PG log lines with temporary file info like this:
case 1: log line with no contextual info
2021-07-07 20:28:15 UTC:10.100.11.95(50274):myapp@mydb:[35200]:LOG:
temporary file: path "base/pgsql_tmp/pgsql_tmp35200.0", size 389390336
case 2: log line with contextual info
2021-07-07 20:56:18 UTC:172.16.193.118(56080):myapp@mydb:[22418]:LOG:
temporary file: path "base/pgsql_tmp/pgsql_tmp22418.0", size 1048576000
2021-07-07 20:56:18
UTC:172.16.193.118(56080):myapp@mydb:[22418]:CONTEXT: PL/pgSQL function
memory.f_memory_usage(boolean) line 13 at RETURN QUERY
There are at least 2 cases where stuff can spill over to disk:
* queries that don't fit in work_mem, and
* temporary tables that don't fit in temp_buffers
Question, if log_temp_files is turned on (=0), then how can you tell
from where the temporary log line comes from?
I see a pattern where work_mem spill overs have a CONTEXT line that
immediately follows the LOG LINE with keyword, temporary. See case 2 above.
For other LOG lines with keyword, temporary, there is no such pattern.
Could those be the ones caused by temp_buffer spill overs to disk? case
1 above.
I really want to tune temp_buffers, but I would like to be able to
detect when temporary tables are spilling over to disk, so that I can
increase temp_buffers.
Any help would be appreciated.
I am not sure if you can istinguish those two cases from the log.
What I would do is identify the problematic query and run it with
EXPLAIN (ANALYZE, BUFFERS). Then you should see which part of the query
creates the temporary files.
If it is a statement in a function called from your top level query,
auto_explain with the correct parameters can get you that output for
those statements too.
Yours,
Laurenz Albe
