On Mon, Jul 22, 2019 at 11:30:37AM +0300, Heikki Linnakangas wrote:
On 18/07/2019 21:24, Jeff Davis wrote:
Previous discussion:
https://postgr.es/m/1407012053.15301.53.camel%40jeff-desktop
This patch introduces a way to ask a memory context how much memory it
currently has allocated. Each time a new block (not an individual
chunk, but a new malloc'd block) is allocated, it increments a struct
member; and each time a block is free'd, it decrements the struct
member. So it tracks blocks allocated by malloc, not what is actually
used for chunks allocated by palloc.
The purpose is for Memory Bounded Hash Aggregation, but it may be
useful in more cases as we try to better adapt to and control memory
usage at execution time.
Seems handy.
Indeed.
* I changed it to only update mem_allocated for the current context,
not recursively for all parent contexts. It's now up to the function
that reports memory usage to recurse or not (as needed).
Is that OK for memory bounded hash aggregation? Might there be a lot
of sub-contexts during hash aggregation?
There shouldn't be, at least not since b419865a814abbc. There might be
cases where custom aggregates still do that, but I think that's simply a
design we should discourage.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
