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.albe@xxxxxxxxxxx> 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
