Re: "type with xxxx does not exist" when doing ExecMemoize()

On Mon, Feb 26, 2024 at 3:54 PM Andrei Lepikhov <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.

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.

The ResetExprContext call in MemoizeHash_hash was introduced in
0b053e78b to fix a memory leak issue.

commit 0b053e78b5990cd01e7169ee5bd2bb8e4045deea
Author: David Rowley <drowley@postgresql.org>
Date:   Thu Oct 5 20:30:47 2023 +1300

    Fix memory leak in Memoize code

It seems to me that switching to the per-tuple memory context is
sufficient to fix the memory leak.  Calling ResetExprContext in
MemoizeHash_hash each time seems too aggressive.

I tried to remove the ResetExprContext call in MemoizeHash_hash and did
not see the memory leak with the repro query in [1].

diff --git a/src/backend/executor/nodeMemoize.c
b/src/backend/executor/nodeMemoize.c
index 18870f10e1..f2f025520d 100644
--- a/src/backend/executor/nodeMemoize.c
+++ b/src/backend/executor/nodeMemoize.c
@@ -207,7 +207,6 @@ MemoizeHash_hash(struct memoize_hash *tb, const
MemoizeKey *key)
                }
        }

-       ResetExprContext(econtext);
        MemoryContextSwitchTo(oldcontext);
        return murmurhash32(hashkey);
 }

Looping in David to have a look.

[1]
https://www.postgresql.org/message-id/flat/83281eed63c74e4f940317186372abfd%40cft.ru

Thanks
Richard