Thread: Re: freeing bms explicitly

Hi,

I was looking at calls to bms_free() in PG code.

e.g. src/backend/commands/publicationcmds.c line 362

        bms_free(bms);

The above is just an example, there're other calls to bms_free().

Since the bms is allocated from some execution context, I wonder why this call is needed.

When the underlying execution context wraps up, isn't the bms freed ?

Cheers

Zhihong Yu <zyu@yugabyte.com> writes:
>> I was looking at calls to bms_free() in PG code.
>> e.g. src/backend/commands/publicationcmds.c line 362
>>      bms_free(bms);
>> The above is just an example, there're other calls to bms_free().
>> Since the bms is allocated from some execution context, I wonder why this
>> call is needed.
>>
>> When the underlying execution context wraps up, isn't the bms freed ?

Yeah, that's kind of pointless --- and the pfree(rfnode) after it is even
more pointless, since it'll free only the top node of that expression
tree.  Not to mention the string returned by TextDatumGetCString, and
whatever might be leaked during the underlying catalog accesses.

If we were actually worried about transient space consumption of this
function, it'd be necessary to do a lot more than this.  It doesn't
look to me like it's worth worrying about though -- it doesn't seem
like it could be hit more than once per query in normal cases.

                        regards, tom lane

On Tue, Mar 22, 2022 at 3:39 AM Zhihong Yu <zyu@yugabyte.com> wrote:
>
> On Mon, Mar 21, 2022 at 3:05 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>
>> Zhihong Yu <zyu@yugabyte.com> writes:
>> >> I was looking at calls to bms_free() in PG code.
>> >> e.g. src/backend/commands/publicationcmds.c line 362
>> >>      bms_free(bms);
>> >> The above is just an example, there're other calls to bms_free().
>> >> Since the bms is allocated from some execution context, I wonder why this
>> >> call is needed.
>> >>
>> >> When the underlying execution context wraps up, isn't the bms freed ?
>>
>> Yeah, that's kind of pointless --- and the pfree(rfnode) after it is even
>> more pointless, since it'll free only the top node of that expression
>> tree.  Not to mention the string returned by TextDatumGetCString, and
>> whatever might be leaked during the underlying catalog accesses.
>>
>> If we were actually worried about transient space consumption of this
>> function, it'd be necessary to do a lot more than this.  It doesn't
>> look to me like it's worth worrying about though -- it doesn't seem
>> like it could be hit more than once per query in normal cases.
>>
>>                         regards, tom lane
>
>
> Thanks Tom for replying.
>
> What do you think of the following patch ?
>

Your patch looks good to me. I have found one more similar instance in
the same file and changed that as well accordingly. Let me know what
you think of the attached?

--
With Regards,
Amit Kapila.

On Tue, Mar 22, 2022 at 8:45 PM Amit Kapila <amit.kapila16@gmail.com> wrote:

On Tue, Mar 22, 2022 at 3:39 AM Zhihong Yu <zyu@yugabyte.com> wrote:
>
> On Mon, Mar 21, 2022 at 3:05 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>
>> Zhihong Yu <zyu@yugabyte.com> writes:
>> >> I was looking at calls to bms_free() in PG code.
>> >> e.g. src/backend/commands/publicationcmds.c line 362
>> >>      bms_free(bms);
>> >> The above is just an example, there're other calls to bms_free().
>> >> Since the bms is allocated from some execution context, I wonder why this
>> >> call is needed.
>> >>
>> >> When the underlying execution context wraps up, isn't the bms freed ?
>>
>> Yeah, that's kind of pointless --- and the pfree(rfnode) after it is even
>> more pointless, since it'll free only the top node of that expression
>> tree.  Not to mention the string returned by TextDatumGetCString, and
>> whatever might be leaked during the underlying catalog accesses.
>>
>> If we were actually worried about transient space consumption of this
>> function, it'd be necessary to do a lot more than this.  It doesn't
>> look to me like it's worth worrying about though -- it doesn't seem
>> like it could be hit more than once per query in normal cases.
>>
>>                         regards, tom lane
>
>
> Thanks Tom for replying.
>
> What do you think of the following patch ?
>

Your patch looks good to me. I have found one more similar instance in
the same file and changed that as well accordingly. Let me know what
you think of the attached?

--
With Regards,
Amit Kapila.

 

Hi, Amit:

The patch looks good to me.

Cheers