valgrind a background worker

=?UTF-8?Q?Jon_Erdman?= <jon@thewickedtribe.net> writes:

I've got a background worker that has a slow memory leak in it
somewhere. How can I get it to start under valgrind to get a memcheck
output from it?

You have to valgrind the whole cluster AFAIK. Basically, start
the postmaster under valgrind with --trace-children=yes.
For leak tracking you probably also want
--leak-check=full --track-origins=yes --read-var-info=yes

regards, tom lane

Aha! Thanks Tom! This will be my first time using valgrind, so I was unaware of trace-children, and getting it to attach to forked stuff was exactly where I thought the difficulty would lie.

This is great, much appreciated!

I’m suspecting that the leak might be coming from initStringInfo(), as I see a palloc() in there and no associated pfree() in my background worker’s code, but looking at the elog backend code, it looks like maybe you only have to explicitly free buf if you relocate it larger?
--
Jon Erdman

=?UTF-8?Q?Jon_Erdman?= <jon@thewickedtribe.net> writes:

I’m suspecting that the leak might be coming from initStringInfo(), as I see a palloc() in there and no associated pfree() in my background worker’s code, but looking at the elog backend code, it looks like maybe you only have to explicitly free buf if you relocate it larger?

Usually it's more like "you need to pfree if you allocated in a long-lived
memory context". elog is working in ErrorContext which it expects will
be reset when the dust settles.

regards, tom lane

On Fri, Feb 10, 2023 at 10:04 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:

=?UTF-8?Q?Jon_Erdman?= <jon@thewickedtribe.net> writes:

I've got a background worker that has a slow memory leak in it
somewhere. How can I get it to start under valgrind to get a memcheck
output from it?

You have to valgrind the whole cluster AFAIK. Basically, start
the postmaster under valgrind with --trace-children=yes.
For leak tracking you probably also want
--leak-check=full --track-origins=yes --read-var-info=yes

One additional comment... the program in question and PostgreSQL
should also be built with -g -O1 per
https://valgrind.org/docs/manual/quick-start.html . Otherwise, there's
a risk the line information will not be accurate or usable.

Jeff

Jeffrey Walton <noloader@gmail.com> writes:

On Fri, Feb 10, 2023 at 10:04 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:

You have to valgrind the whole cluster AFAIK. Basically, start
the postmaster under valgrind with --trace-children=yes.
For leak tracking you probably also want
--leak-check=full --track-origins=yes --read-var-info=yes

One additional comment... the program in question and PostgreSQL
should also be built with -g -O1 per
https://valgrind.org/docs/manual/quick-start.html . Otherwise, there's
a risk the line information will not be accurate or usable.

Yeah. Also, you need to compile Postgres with -DUSE_VALGRIND
if you want valgrind to have any idea about palloc/pfree.

regards, tom lane

On 2/10/23 3:05 PM, Tom Lane wrote:

Jeffrey Walton <noloader@gmail.com> writes:

On Fri, Feb 10, 2023 at 10:04 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:

You have to valgrind the whole cluster AFAIK. Basically, start
the postmaster under valgrind with --trace-children=yes.
For leak tracking you probably also want
--leak-check=full --track-origins=yes --read-var-info=yes

One additional comment... the program in question and PostgreSQL
should also be built with -g -O1 per
https://valgrind.org/docs/manual/quick-start.html . Otherwise, there's
a risk the line information will not be accurate or usable.

Yeah. Also, you need to compile Postgres with -DUSE_VALGRIND
if you want valgrind to have any idea about palloc/pfree.

Thanks much both of you! I'll report back how it goes ;)
--
Jon Erdman (aka StuckMojo)
PostgreSQL Zealot

On 2/10/23 9:08 PM, Jon Erdman wrote:

On 2/10/23 3:05 PM, Tom Lane wrote:

Jeffrey Walton <noloader@gmail.com> writes:

On Fri, Feb 10, 2023 at 10:04 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:

You have to valgrind the whole cluster AFAIK.  Basically, start
the postmaster under valgrind with --trace-children=yes.
For leak tracking you probably also want
--leak-check=full --track-origins=yes --read-var-info=yes

One additional comment... the program in question and PostgreSQL
should also be built with -g -O1 per
https://valgrind.org/docs/manual/quick-start.html . Otherwise, there's
a risk the line information will not be accurate or usable.

Yeah.  Also, you need to compile Postgres with -DUSE_VALGRIND
if you want valgrind to have any idea about palloc/pfree.

Thanks much both of you! I'll report back how it goes ;)

FYI folks: once I got the build done properly (valgrind brew wouldn't
install on OSX) on linux, I was able to find and fix my leaks. They were
from not calling pfree on StringInfo.data.
--
Jon Erdman (aka StuckMojo)
    PostgreSQL Zealot