On 26/2/2024 18:34, Richard Guo wrote:
>
> On Mon, Feb 26, 2024 at 3:54 PM Andrei Lepikhov
> <a.lepikhov@postgrespro.ru <mailto:a.lepikhov@postgrespro.ru>> wrote:
>
> On 26/2/2024 12:44, Tender Wang wrote:
> > Make sense. I found MemoizeState already has a MemoryContext, so
> I used it.
> > I update the patch.
> This approach is better for me. In the next version of this patch, I
> included a test case. I am still unsure about the context chosen and
> the
> stability of the test case. Richard, you recently fixed some Memoize
> issues, could you look at this problem and patch?
>
>
> I looked at this issue a bit. It seems to me what happens is that at
> first the memory areas referenced by probeslot->tts_values[] are
> allocated in the per tuple context (see prepare_probe_slot). And then
> in MemoizeHash_hash, after we've calculated the hashkey, we will reset
> the per tuple context. However, later in MemoizeHash_equal, we still
> need to reference the values in probeslot->tts_values[], which have been
> cleared.
Agree
>
> Actually the context would always be reset in MemoizeHash_equal, for
> both binary and logical mode. So I kind of wonder if it's necessary to
> reset the context in MemoizeHash_hash.
I can only provide one thought against this solution: what if we have a
lot of unique hash values, maybe all of them? In that case, we still
have a kind of 'leak' David fixed by the commit 0b053e78b5.
Also, I have a segfault report of one client. As I see, it was caused by
too long text column in the table slot. As I see, key value, stored in
the Memoize hash table, was corrupted, and the most plain reason is this
bug. Should we add a test on this bug, and what do you think about the
one proposed in v3?
--
regards,
Andrei Lepikhov
Postgres Professional