logical replication initial copy and WAL generation - Mailing list pgsql-general

From Radoslav Nedyalkov
Subject logical replication initial copy and WAL generation
Date
Msg-id CANhtRiZkq+D5Wj+rnAapma1W2KPhFp24z8tpu=gYK4Est+PNgQ@mail.gmail.com
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Responses Re: logical replication initial copy and WAL generation
List pgsql-general
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 ?! 

Thank you very much,

Rado

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