Re: Proposed patch: synchronized_scanning GUC variable

On Sun, 2008-01-27 at 15:07 -0500, Tom Lane wrote:
> Per today's -hackers discussion, add a GUC variable to allow clients to
> disable the new synchronized-scanning behavior, and make pg_dump disable
> sync scans so that it will reliably preserve row ordering. This is a
> pretty trivial patch, but seeing how late we are in the 8.3 release
> cycle, I thought I'd better post it for comment anyway.

I apologize for the late reply, but I have one comment I'd like to add.

> + if (g_fout->remoteVersion >= 80300)
> + do_sql_command(g_conn, "SET synchronized_scanning TO off");
> +
> + /*
> * Start serializable transaction to dump consistent data.
> */

I think that pg_dump is a reasonable use case for synchoronized scans
when the table has not been clustered. It could potentially make pg_dump
have much less of a performance impact when run against an active
system.

I think it's worth considering enabling sync scans for non-clustered
tables if it would not interfere with the release. Of course, a painless
8.3 release is the top priority.

Regards,
Jeff Davis