On 10/8/2023 15:33, Ashutosh Bapat wrote:
On Wed, Aug 9, 2023 at 8:56 PM David Rowley <dgrowle...@gmail.com> wrote:
On Thu, 10 Aug 2023 at 03:12, Ashutosh Bapat
<ashutosh.bapat....@gmail.com> wrote:
I guess it depends on the problem you're trying to solve. I had
thought you were trying to do some work to reduce the memory used by
the planner, so I imagined you wanted this so you could track your
progress and also to help ensure we don't make too many mistakes in
the future which makes memory consumption worse again.
Another way we might go about reducing planner memory is to make
changes to the allocators themselves. For example, aset rounds up to
the next power of 2. If we decided to do something like add more
freelists to double the number so we could add a mid-way point
freelist between each power of 2, then we might find it reduces the
planner memory by, say 12.5%. If we just tracked what was consumed by
palloc() that would appear to save us nothing, but it might actually
save us several malloced blocks.
This won't just affect planner but every subsystem of PostgreSQL, not
just planner, unless we device a new context type for planner.
My point is what's relevant here is how much net memory planner asked
for. Internally how much memory PostgreSQL allocated seems relevant
for the memory context infra as such but not so much for planner
alone.
If you think that memory allocated is important, I will add both used
and (net) allocated memory to EXPLAIN output.
As a developer, I like having as much internal info in my EXPLAIN as
possible. But this command is designed mainly for users, not core
developers. The size of memory allocated usually doesn't make sense for
users. On the other hand, developers can watch it easily in different
ways, if needed. So, I vote for the 'memory used' metric only.
The patch looks good, passes the tests.
--
regards,
Andrey Lepikhov
Postgres Professional
