Re: Using per-transaction memory contexts for storing decoded tuples - Mailing list pgsql-hackers

On Fri, Oct 11, 2024 at 3:40 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> Please find the attached patches.
>

@@ -343,9 +343,9 @@ ReorderBufferAllocate(void)
  */
  buffer->tup_context = GenerationContextCreate(new_ctx,
    "Tuples",
-   SLAB_LARGE_BLOCK_SIZE,
-   SLAB_LARGE_BLOCK_SIZE,
-   SLAB_LARGE_BLOCK_SIZE);
+   SLAB_DEFAULT_BLOCK_SIZE,
+   SLAB_DEFAULT_BLOCK_SIZE,
+   SLAB_DEFAULT_BLOCK_SIZE);

Shouldn't we change the comment atop this change [1] which states that
we should benchmark the existing values?

One more thing we kept the max size as SLAB_DEFAULT_BLOCK_SIZE instead
of something like we do with ALLOCSET_DEFAULT_SIZES, so we can
probably write a comment as to why we choose to use the max_size same
as init_size. BTW, can we once try to use the max size as
SLAB_LARGE_BLOCK_SIZE? Can it lead to the same problem with concurrent
transactions where freeing larger blocks could be a problem, if so, we
can at least write a comment for future reference.

[1] -
/*
* XXX the allocation sizes used below pre-date generation context's block
* growing code.  These values should likely be benchmarked and set to
* more suitable values.
*/

--
With Regards,
Amit Kapila.