Re: Speedup twophase transactions

On Tue, Jan 12, 2016 at 4:57 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
> Performance tests for me show that the patch is effective; my results match
> Jesper's roughly in relative numbers.
>
> My robustness review is that the approach and implementation are safe.
>
> It's clear there are various additional tuning opportunities, but the
> objective of the current patch to improve performance is very, very clearly
> met, so I'm aiming to commit *this* patch soon.

-       /* initialize LSN to 0 (start of WAL) */
-       gxact->prepare_lsn = 0;
+       /* initialize LSN to InvalidXLogRecPtr */
+       gxact->prepare_start_lsn = InvalidXLogRecPtr;
+       gxact->prepare_end_lsn = InvalidXLogRecPtr;

I think that it would be better to explicitly initialize gxact->ondisk
to false here.

+       xlogreader = XLogReaderAllocate(&logical_read_local_xlog_page, NULL);
+       if (!xlogreader)
+               ereport(ERROR,
+                               (errcode(ERRCODE_OUT_OF_MEMORY),
+                                errmsg("out of memory"),
+                                errdetail("Failed while allocating an
XLog reading processor.")));
Depending on something that is part of logical decoding to decode WAL
is not a good idea. If you want to move on with this approach, you
should have a dedicated function. Even better, it would be nice to
come up with a generic function used by both 2PC and logical decoding.
-- 
Michael