[PATCH] remove condition always true (/src/backend/access/heap/vacuumlazy.c)

Hi,

On 2020-03-30 15:07:40 -0300, Ranier Vilela wrote:

I'm not sure that the patch is 100% correct.

This is *NOT* correct.

But the fix is about expression about always true.
But if this patch is correct, he fix one possible bug.

The comment says:
* Perform checking of FSM after releasing lock, the fsm is
* approximate, after all.

But this is not what the code does, apparently it checks before unlocking.

No, it doesn't. The freespace check isn't the PageIsNew(), it's the
GetRecordedFreeSpace() call. Which happens after unlocking.

Greetings,

Andres Freund

Em seg., 30 de mar. de 2020 às 18:14, Andres Freund <andres@anarazel.de>
escreveu:

Hi,

On 2020-03-30 14:10:29 -0700, Andres Freund wrote:

On 2020-03-30 17:08:01 -0300, Ranier Vilela wrote:

Em seg., 30 de mar. de 2020 às 16:05, Andres Freund <

andres@anarazel.de>

escreveu:

Hi,

On 2020-03-30 15:07:40 -0300, Ranier Vilela wrote:

I'm not sure that the patch is 100% correct.

This is *NOT* correct.

Anyway, the original source, still wrong.
What is the use of testing PageIsNew (page) twice in a row, if nothing

has

changed.

Yea, that can be reduced. It's pretty harmless though.

We used to require a cleanup lock (which requires dropping the lock,
acquiring a cleanup lock - which allows for others to make the page be
not empty) before acting on the empty page in vacuum. That's why
PageIsNew() had to be checked again.

Well, this is what the patch does, promove reduced and continue to check
PageIsNew after unlock.

regards,
Ranier Vilela

Hi,
Thanks for the commit.

Ranier Vilela