Question about UpdateFullPageWrites() at the end of recovery.

Hi,

I have a question about the comment of UpdateFullPageWrites() called
at the end of recovery (in StartupXLOG()):

/*
* Update full_page_writes in shared memory and write an XLOG_FPW_CHANGE
* record before resource manager writes cleanup WAL records or checkpoint
* record is written.
*/
Insert->fullPageWrites = lastFullPageWrites;
UpdateFullPageWrites();

The comment says that it expects to write an XLOG_FPW_CHANGE record
there but that record is not actually written as it's still in
recovery (i.e., RecoveryInProgress() still returns true). Which seems
inconsistent.

Even if we replay XLOG_FPW_CHANGE during the recovery, we just change
the lastFullPageWrites, and at the end of the recovery, we anyway set
the value of full_page_writes in the config file to
Insert->fullPageWrites before accepting writes. Also, the
full-page-write state on the standby doesn't affect taking backups on
standby as we forcibly enable full-page-writes during taking a backup.
So I thought it would not be a problem even if we don't write
XLOG_FPW_CHANGE there, but I might be missing something.

Should we revise the comment? or change the code so it can write that record?

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com