I am trying to understand how memory is allocated/used by our Postgresql Database connections. From reading the documentation it appears that work_mem and temp_buffers are the 2 largest contributors (and work_mem usage can grow) to the memory utilized
by the Database connections. In addition, if I understand correctly, work_mem and temp_buffers each have their own pool, and thus database connections use (when needed) and return memory to these pools. I have not read this anywhere, but based on observation
it appears that once these pools grow, they never release any of the memory (e.g. they do not shrink in size if some of the memory has not been for a given period of time).
With that said, are there any mechanisms available to determine how much work_mem and temp_buffers memory has been allocated by the Postgres database (and by database connection/process would be very useful as well)? Also, which postgres process manages
the memory pools for work_mem and temp_buffers?
FYI – I am using smem (on a linux server) to monitor the memory allocated to our Database connections. In an attempt to lower our memory footprint, I lowered our setting for work_mem from 1MB down to 500kB (in addition I enabled log_temp_files to see
the SQL statements that now use temp files for sorting and hash operations). As I expected the memory used by the connections that were doing large sorts went down in size. However, one of those DB connections dramatically increased in memory usage with this
change. It went from approx. 6MB up to 37MB in memory usage? Are temp_buffers used in conjunction with some sorting operations that use temp_files (and thus this connection allocated several temp_buffers? Although I thought the temp_buffers parameter was
the amount of memory that would be allocated for a session (e.g. there is no multiplying factor like the work_mem for a session)?
We are using Postgres 9.0.13
shared_buffers = 800MB
work_mem = 1MB
temp_buffers = 8MB (our applications do not use temp tables)
effective_cache_size = 1500MB
Thanks,
Alan
