Horton

Re: Enable data checksums by default

Peter Eisentraut <peter@eisentraut.org>

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From: Peter Eisentraut <peter@eisentraut.org>
To: pgsql-hackers <pgsql-hackers@postgresql.org>
Cc: Greg Sabino Mullane <htamfids@gmail.com>, Robert Haas <robertmhaas@gmail.com>
Date: 2024-08-22T06:11:06Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Avoid BufferGetLSNAtomic() calls during nbtree scans.

  2. doc PG 18 relnotes: Add incompatibility note about checksums now default

  3. Fix pg_upgrade's cross-version tests when old < 18

  4. initdb: Change default to using data checksums.

  5. Allow TAP tests to force checksums off when calling init()

  6. initdb: Add new option "--no-data-checksums"

  7. Tweak docs to reduce possible impact of data checksums

Attachments

On 15.08.24 08:38, Peter Eisentraut wrote:
> On 08.08.24 19:42, Robert Haas wrote:
>>> I'm thinking pg_upgrade could have a mode where it adds the
>>> checksum during the upgrade as it copies the files (essentially a subset
>>> of pg_checksums).  I think that would be useful for that middle tier of
>>> users who just want a good default experience.
>> That would be very nice.
> 
> Here is a demo patch for that.  It turned out to be quite simple.
> 
> I wrote above about a separate mode for that (like 
> --copy-and-make-adjustments), but it was just as easy to stick it into 
> the existing --copy mode.
> 
> It would be useful to check what the performance overhead of this is 
> versus a copy that does not have to make adjustments.  I expect it's 
> very little.
> 
> A drawback is that as written this does not work on Windows, because 
> Windows uses a different code path in copyFile().  I don't know the 
> reasons for that.  But it would need to be figured out.

Here is an updated patch for this.  I simplified the logic a bit and 
also handle the case where the read() reads less than a round number of 
blocks.  I did some performance testing.  The overhead of computing the 
checksums versus a straight --copy without checksum adjustments appears 
to be around 5% wall clock time, which seems ok to me.  I also looked 
around the documentation to see if there is anything to update, but 
didn't find anything.

I think if we can work out what to do on Windows, this could be a useful 
little feature for facilitating $subject.