Re: logical replication initial copy and WAL generation

We have wal_log_hints = off.
Then I thought hint bits are never WAL logged.
Or am I missing the part - they are, upon first read ?

Thanks again
Rado

On Wed, May 19, 2021 at 3:56 PM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
wrote:

> On Wed, 2021-05-19 at 14:16 +0300, Radoslav Nedyalkov wrote:
> > Hello Forum,
> > I know it sounds weird but we have faced it a couple of times already
> and have no idea.
> > We're trying to establish logical replication from RDS(10.9) to
> RDS(12.5).
> > We're adding tables to the publication one by one.
> > During the initial copy for some tables we experience huge WAL
> generation on the source db.
> > From 0.5mb/s it jumps to 15MB/s.
> > This happens when a copy just started or in the middle or at the end.
> > WAL generation causes service statements to wait on WALWriteLock causing
> high response time.
> >
> > Any idea how the initial copy can cause WAL generation ?!
>
> I don't know how much RDS is like PostgreSQL, but on PostgreSQL this could
> be
> the setting of hint bits for new rows that have never been read before.
>
> Yours,
> Laurenz Albe
> --
> Cybertec | https://www.cybertec-postgresql.com
>
>