Hi.
Trying to monitor perf during the initial tablesync phase (COPY) right after CREATE SUBSCRIPTION. I noticed that the size of 17/main/base/pgsql_tmp on the destination node grows (tens of gigabytes) as the COPY command (running internally on the publisher) progresses. Then in the end (when its "EXPLAIN SELECT 1 FROM tbl" on the destination shows the approximate number of rows equals to the number of rows on the source node) it hangs for several minutes, and then 17/main/base/pgsql_tmp empties, and the subscription progresses.
It seems like if I increase work_mem to several GB, then the growth of 17/main/base/pgsql_tmp becomes less significant.
Questions:
1. Are there some diagnostics commands that would allow me to figure out what is in those tmp files? Why does the subscriber create those tmp files and not just write directly to the data files and WAL? (The table has 2 bytea columns, i.e. it's TOASTed for sure.)
2. Is there a way to set work_mem only for "logical replication tablesync worker"? I don't want to have it that high for all connections, but for logical replication tablesync worker - it's fine to have it set to a huge value (I have max_sync_workers_per_subscription=1, so there is not more than 1 of such processes in the system).
3. Is this work_mem consideration relevant at all? Maybe it's a red herring?
Thanks!
