Re: BUG #19411: libpq 16.x exhibits a memory leak when connections are repeatedly created and destroyed

Hi,

On 2026-02-17 13:47:49 -0500, Tom Lane wrote:
> Matt Carter <Matt(dot)Carter(at)twosigma(dot)com> writes:
> > Thank you for taking the time to test this and for the feedback. Your C test showing no leak suggests the issue is specific to how psycopg2 uses libpq, not libpq itself. I apologize for not including enough environmental details. I used Kerberos/GSSAPI with SSL (TLS 1.2 connections). My connection string was: "postgresql://hostname/database" (no password, Kerberos auth).
> > Your mention of "years ago libpq did leak memory while using GSSAPI encryption" is interesting because we ARE using GSSAPI/Kerberos authentication.
>
> Interesting. I wondered about GSSAPI, but spinning up such an
> environment is more work than I wanted to do on speculation.

Heh, understandable...

> > I can test with non-GSSAPI authentication to try to isolate that variable. I can also create a pure psycopg2 reproducer (without SQLAlchemy). I can also test whether disabling GSSAPI encryption (but keeping GSSAPI auth) changes the behavior. Would testing with GSSAPI authentication help narrow this down? I can also report this to the psycopg2 project if you think it's their issue.
>
> Please try varying the connection type and encryption. I do suspect
> this may be psycopg2's fault, but we lack enough data to pin blame
> as yet.

Matt, you could try analyzing the memory usage with heaptrack, it tends to be
pretty good at finding them even in uninstrumented builds, as long as enough
debug symbols for a backtrace are available. Often enough it'll pinpoint
where the leak is coming from quite easily (but note that it will report some
constant-sized leaks that are "intentional").

Greetings,

Andres