On Thu, Apr 23, 2020 at 12:16 PM Peter Eisentraut <peter.eisentr...@2ndquadrant.com> wrote: > > On 2020-04-23 07:31, Julien Rouhaud wrote: > > I agree that full page writes can be used in this case, but I'm > > wondering if that can be misleading for some reader which might e.g. > > confuse with the full_page_writes GUC. And as Justin pointed out, the > > documentation for now usually mentions "full page image(s)" in such > > cases. > > ISTM that in the context of this patch, "full-page image" is correct. A > "full-page write" is what you do to a table or index page when you are > recovering a full-page image. >
So what do we call when we log the page after it is touched after checkpoint? I thought we call that as full-page write. > The internal symbol for the WAL record is > XLOG_FPI and xlogdesc.c prints it as "FPI". > That is just one way/reason we log the page. There are others as well. I thought here we are computing the number of full-page writes happened in the system due to various reasons like (a) a page is operated upon first time after the checkpoint, (b) log the XLOG_FPI record, (c) Guc for WAL consistency checker is on, etc. If we see in XLogRecordAssemble where we decide to log this information, there is a comment " .... log a full-page write for the current block." and there was an existing variable with 'fpw_lsn' which indicates to an extent that what we are computing in this patch is full-page writes. But there is a reference to full-page image as well. I think as full_page_writes is an exposed variable that is well understood so exposing information with similar name via this patch doesn't sound illogical to me. Whatever we use here we need to be consistent all throughout, even pg_stat_statements need to name exposed variable as wal_fpi instead of wal_fpw. To me, full-page writes sound more appealing with other WAL usage variables like records and bytes. I might be more used to this term as 'fpw' that is why it occurred better to me. OTOH, if most of us think that a full-page image is better suited here, I am fine with changing it at all places. With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com