Re: logical replication initial copy and WAL generation

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
--
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