Re: Making aggregate deserialization (and WAL receive) functions slightly faster

On Wed, 11 Oct 2023 at 08:52, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> David Rowley <dgrowleyml@gmail.com> writes:
> > I've attached a slightly more worked on patch that makes maxlen == 0
> > mean read-only.  Unsure if a macro is worthwhile there or not.
>
> A few thoughts:

Thank you for the review.

I spent more time on this and did end up with 2 new init functions as
you mentioned.  One for strictly read-only (initReadOnlyStringInfo),
which cannot be appended to, and as you mentioned, another
(initStringInfoFromString) which can accept a palloc'd buffer which
becomes managed by the stringinfo code. I know these names aren't
exactly as you mentioned. I'm open to adjusting still.

This means I got rid of the read-only conversion code in
enlargeStringInfo().  I didn't do anything to try to handle buffer
enlargement more efficiently in enlargeStringInfo() for the case where
initStringInfoFromString sets maxlen to some non-power-of-2.  The
doubling code seems like it'll work ok without power-of-2 values,
it'll just end up calling repalloc() with non-power-of-2 values.

I did also wonder if resetStringInfo() would have any business
touching the existing buffer in a read-only StringInfo and came to the
conclusion that it wouldn't be very read-only if we allowed
resetStringInfo() to do its thing on it. I added an Assert to fail if
resetStringInfo() receives a read-only StringInfo.

Also, since it's still being discussed, I left out the adjustment to
LogicalParallelApplyLoop().  That also allows the tests to pass
without the failing Assert that was checking for the NUL terminator.

David