Horton

Re: Potential G2-item cycles under serializable isolation

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Kevin Grittner <kgrittn@gmail.com>, Jeff Davis <pgsql@j-davis.com>, PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>, Kyle Kingsbury <aphyr@jepsen.io>
Date: 2020-06-09T02:00:58Z
Lists: pgsql-bugs 
On Tue, Jun 9, 2020 at 1:26 PM Peter Geoghegan <pg@bowt.ie> wrote:
> The functionality in question (the code from the
> HeapCheckForSerializableConflictOut() case statement) was originally
> discussed here, with the details finalized less than a week before SSI
> was committed in 2011:
>
> https://www.postgresql.org/message-id/flat/1296499247.11513.777.camel%40jdavis#9e407424df5f8794360b6e84de60200a
>
> It hasn't really changed since that time.

Right, the only change was to move things around a bit to suport new
table AMs.  Speaking of which, it looks like the new comment atop
CheckForSerializableConflictOut() could use some adjustment.  It says
"A table AM is reading a tuple that has been modified.  After
determining that it is visible to us, it should call this function..."
but it seems the truth is a bit more complicated than that.

Commits

  1. Doc: Add references for SI and SSI.

  2. Improve comments for [Heap]CheckForSerializableConflictOut().

  3. Avoid update conflict out serialization anomalies.

  4. Implement genuine serializable isolation level.