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Thread: missing PG_FREE_IF_COPY in textlike() and textnlike() ?

missing PG_FREE_IF_COPY in textlike() and textnlike() ?

From
CK Tan
Date:
Hi Hackers,

I see in the texteq() function calls to DatumGetTextPP() are followed
by conditional calls to PG_FREE_IF_COPY. e.g.

https://github.com/postgres/postgres/blob/master/src/backend/utils/adt/varlena.c#L1792

   text *targ1 = DatumGetTextPP(arg1);
   text *targ2 = DatumGetTextPP(arg2);
   result = (memcmp(VARDATA_ANY(targ1), VARDATA_ANY(targ2), len1 -
VARHDRSZ) == 0);
   PG_FREE_IF_COPY(targ1, 0);
   PG_FREE_IF_COPY(targ2, 1);

However, in textlike(), PG_FREE_IF_COPY calls are missing.

https://github.com/postgres/postgres/blob/master/src/backend/utils/adt/like.c#L283

Is this a memory leak bug?

Regards,
-cktan

Re: missing PG_FREE_IF_COPY in textlike() and textnlike() ?

From
Tom Lane
Date:
CK Tan <cktan@vitessedata.com> writes:
> I see in the texteq() function calls to DatumGetTextPP() are followed
> by conditional calls to PG_FREE_IF_COPY. e.g.

That's because texteq() is potentially usable as a btree index
function, and btree isn't too forgiving about leaks.

> However, in textlike(), PG_FREE_IF_COPY calls are missing.
> https://github.com/postgres/postgres/blob/master/src/backend/utils/adt/like.c#L283

textlike() isn't a member of any btree opclass.

> Is this a memory leak bug?

Not unless you can demonstrate a case where it causes problems.
For the most part, such functions run in short-lived contexts.

            regards, tom lane

Re: missing PG_FREE_IF_COPY in textlike() and textnlike() ?

From
CK Tan
Date:
Got it. It is a leak-by-design for efficiency.

Thanks,
-cktan

On Fri, Sep 16, 2022 at 12:03 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> CK Tan <cktan@vitessedata.com> writes:
> > I see in the texteq() function calls to DatumGetTextPP() are followed
> > by conditional calls to PG_FREE_IF_COPY. e.g.
>
> That's because texteq() is potentially usable as a btree index
> function, and btree isn't too forgiving about leaks.
>
> > However, in textlike(), PG_FREE_IF_COPY calls are missing.
> > https://github.com/postgres/postgres/blob/master/src/backend/utils/adt/like.c#L283
>
> textlike() isn't a member of any btree opclass.
>
> > Is this a memory leak bug?
>
> Not unless you can demonstrate a case where it causes problems.
> For the most part, such functions run in short-lived contexts.
>
>                         regards, tom lane