Re: Add a perl function in Cluster.pm to generate WAL

On Tue, Dec 19, 2023 at 9:51 AM Michael Paquier <michael@paquier.xyz> wrote:
>
> On Mon, Dec 18, 2023 at 08:48:09AM -0300, Euler Taveira wrote:
> > It is cheaper.
>
> Agreed that this could just use a set of pg_logical_emit_message()
> when jumping across N segments.

Thanks. I missed the point of using pg_logical_emit_message() over
CREATE .. DROP TABLE to generate WAL. And, I agree that it's better
and relatively cheaper in terms of amount of WAL generated.

> Another thing that seems quite
> important to me is to force a flush of WAL with the last segment
> switch, and the new "flush" option of pg_logical_emit_message() can
> be very handy for this purpose.

I used pg_logical_emit_message() in non-transactional mode without
needing an explicit WAL flush as the pg_switch_wal() does a WAL flush
at the end [1].

Attached v4 patch.

[1]
    /*
     * If this was an XLOG_SWITCH record, flush the record and the empty
     * padding space that fills the rest of the segment, and perform
     * end-of-segment actions (eg, notifying archiver).
     */
    if (class == WALINSERT_SPECIAL_SWITCH)
    {
        TRACE_POSTGRESQL_WAL_SWITCH();
        XLogFlush(EndPos);

--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com