Re: pg_walinspect memory leaks

On Sat, Feb 18, 2023 at 5:07 AM Jeff Davis  wrote:
>
> On Thu, 2023-02-16 at 18:00 +0530, Bharath Rupireddy wrote:
> > I'm attaching the patches here. For HEAD, I'd
> > want to be a bit defensive and use the temporary memory context for
> > pg_get_wal_fpi_info() too.
>
> I don't see why we shouldn't backpatch that, too?

pg_get_wal_fpi_info() is added in v16, so backpatching isn't necessary.

> Also, it seems like we should do the same thing for the loop in
> GetXLogSummaryStats(). Maybe just for the outer loop is fine (the inner
> loop is only 16 elements); though again, there's not an obvious
> downside to fixing that, too.

Firstly, WAL record traversing loop in GetWalStats() really doesn't
leak memory, because it just increments some counters and doesn't
palloc any memory. Similarly, the loops in GetXLogSummaryStats() too
don't palloc any memory, so no memory leak. I've seen no memory growth
during execution of pg_get_wal_stats_till_end_of_wal() for 35million
WAL records, see [1] PID 543967 (during the execution of the stats
function, the memory usage remained constant). Therefore, I feel that
the fix isn't required for GetWalStats().

[1]
   PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+
COMMAND
 543967 ubuntu    20   0  168668 152056 149988 R  99.7   0.5   1:33.72
postgres
 412271 ubuntu    20   0 1101852 252724  42904 S   1.3   0.8   2:18.36
node
 412208 ubuntu    20   0  965000 112488  36012 S   0.3   0.4   0:23.46
node
 477193 ubuntu    20   0 5837096  34172   9420 S   0.3   0.1   0:00.93
cpptools-srv

--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com