On Tue, Jan 12, 2021 at 09:40:53PM +0900, Masahiko Sawada wrote:
> > This says:
> >
> > https://wiki.postgresql.org/wiki/Transparent_Data_Encryption#Other_requirements
> >
> > wal_log_hints will be enabled automatically in encryption mode.
> >
> > Does that help?
>
> IIUC it helps but not enough. When wal_log_hints is enabled, we write
> a full-page image when updating hint bits if it's the first time
> change for the page since the last checkpoint. But I'm concerned that
> what if we change hint bits again after the page is flushed. We would
> mark the page as dirtied but not write any WAL, leaving the page lsn
> as it is.
I updated the wiki to be:
https://wiki.postgresql.org/wiki/Transparent_Data_Encryption#Other_requirements
wal_log_hints will be enabled automatically in encryption mode. However,
more than one hit change between checkpoints does not cause WAL
activity, which would cause the same LSN to be used for different pages
images.
I think one big question is that, since we are using a streaming cipher,
do we care about hint bit changes showing to users? I actually don't
know. If we do, some kind of dummy LSN record might be required, as you
suggested.
--
Bruce Momjian <bruce@momjian.us> https://momjian.us
EnterpriseDB https://enterprisedb.com
The usefulness of a cup is in its emptiness, Bruce Lee