Hi Michael,
I first use initdb, and set wal_log_hints=off, data_checksums=off, and full_page_writes=on. Starting pg and running for a while.
Then switch over happened, I used the following commands:
1. Old master postgresql.conf set wal_log_hints=on, then start and stop pg.
2. using pg_rewind --target-pgdata=OldMaster --source-server=NewMaster (no error, old master's wal_log_hints has been set to on)
I first use initdb, and set wal_log_hints=off, data_checksums=off, and full_page_writes=on. Starting pg and running for a while.
Then switch over happened, I used the following commands:
1. Old master postgresql.conf set wal_log_hints=on, then start and stop pg.
2. using pg_rewind --target-pgdata=OldMaster --source-server=NewMaster (no error, old master's wal_log_hints has been set to on)
I wonder if this could lead to data corruption.
On Tue, Feb 18, 2025 at 2:27 PM Michael Paquier <michael.paquier@xxxxxxxxx> wrote:
On Mon, Jun 5, 2017 at 9:37 AM, Dylan Luong <Dylan.Luong@xxxxxxxxxxxx> wrote:
> pg_rewind requires that the target server either has the wal_log_hints
> option enabled in postgresql.conf or data checksums enabled when the cluster
> was initialized with initdb.
Yes, this is to make sure that you don't finish with a corrupted
target server if a hint bit is set on a page after a checkpoint. Any
of those options make sure that a full-page write is generated in this
case.
> What is the difference between the two options?
Data checksums calculate 2 bytes of checksum data and write it to each
page that is evicted from shared buffers. Each page read from disk has
its checksum checked. In some workloads, like a heavy read load where
a lot of page evictions happen, this can induce a couple of percents
of performance lost. In my own experience, that's 1~2%.
> What are the advantages and disadvantages between the two?
> Which one is the the preferred option?
If you care more about performance or if you use a file system that
has its own block-level checksum, wal_log_hints would be preferred.
Data checksums offer more guarantees in terms of integrity though when
looking for corrupted data. Things get found more quickly.
--
Michael
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