Re: Add last_commit_lsn to pg_stat_database

The following review has been posted through the commitfest application:
make installcheck-world: tested, passed
Implements feature: tested, passed
Spec compliant: not tested
Documentation: not tested

Hello

I think it is convenient to know the last commit LSN of a database for troubleshooting and monitoring purposes similar to the "pd_lsn" field in a page header that records the last LSN that modifies this page. I am not sure if it can help determine the WAL location to resume / catch up in logical replication as the "confirmed_flush_lsn" and "restart_lsn" in a logical replication slot are already there to figure out the resume / catchup point as I understand. Anyhow, I had a look at the patch, in general it looks good to me. Also ran it against the CI bot, which also turned out fine. Just one small comment though. The patch supports the recording of last commit lsn from 2 phase commit as well, but the test does not seem to have a test on 2 phase commit. In my opinion, it should test whether the last commit lsn increments when a prepared transaction is committed in addition to a regular transaction.

thank you
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Cary Huang
www.highgo.ca