Re: pgsql: Generational memory allocator

I wrote:
> Instead I propose that we should make sure that the palloc request size
> for XLogReaderState->main_data is always maxalign'd. The existing
> behavior in DecodeXLogRecord of palloc'ing it only just barely big
> enough for the current record seems pretty brain-dead performance-wise
> even without this consideration. Generally, if we need to enlarge
> that buffer, we should enlarge it significantly, IMO.

I've confirmed that the attached is sufficient to stop the valgrind crash
on my machine. But as I said, I think we should be more aggressive at
resizing the buffer, to reduce resize cycles. I'm inclined to start out
with a buffer size of 128 or 256 or so bytes and double it when needed.
Anybody have a feeling for a typical size for the "main data" part
of a WAL record?

regards, tom lane