Horton

Remove HeapTuple and Buffer dependency for predicate locking functions

Ashwin Agrawal <aagrawal@pivotal.io>

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From: Ashwin Agrawal <aagrawal@pivotal.io>
To: PostgreSQL mailing lists <pgsql-hackers@postgresql.org>
Date: 2019-06-24T17:41:06Z
Lists: pgsql-hackers

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Proposing following changes to make predicate locking and checking
functions generic and remove dependency on HeapTuple and Heap AM. We
made these changes to help with Zedstore. I think the changes should
help Zheap and other AMs in general.

- Change PredicateLockTuple() to PredicateLockTID(). So, instead of
  passing HeapTuple to it, just pass ItemPointer and tuple insert
  transaction id if known. This was also discussed earlier in [1],
  don't think was done in that context but would be helpful in future
  if such requirement comes up as well.

- CheckForSerializableConflictIn() take blocknum instead of
  buffer. Currently, the function anyways does nothing with the buffer
  just needs blocknum. Also, helps to decouple dependency on buffer as
  not all AMs may have one to one notion between blocknum and single
  buffer. Like for zedstore, tuple is stored across individual column
  buffers. So, wish to have way to lock not physical buffer but
  logical blocknum.

- CheckForSerializableConflictOut() no more takes HeapTuple nor
  buffer, instead just takes xid. Push heap specific parts from
  CheckForSerializableConflictOut() into its own function
  HeapCheckForSerializableConflictOut() which calls
  CheckForSerializableConflictOut(). The alternative option could be
  CheckForSerializableConflictOut() take callback function and
  callback arguments, which gets called if required after performing
  prechecks. Though currently I fell AM having its own wrapper to
  perform AM specific task and then calling
  CheckForSerializableConflictOut() is fine.

Attaching patch which makes these changes.

This way PredicateLockTID(), CheckForSerializableConflictIn() and
CheckForSerializableConflictOut() functions become usable by any AM.


1]
https://www.postgresql.org/message-id/CAEepm%3D2QbqQ_%2BKQQCnhKukF6NEAeq4SqiO3Qxe%2BfHza5-H-jKA%40mail.gmail.com

Commits

  1. Remove dependency on HeapTuple from predicate locking functions.

  2. Optimize PredicateLockTuple().

  3. Optimize TransactionIdIsCurrentTransactionId().

  4. Fix predicate-locking of HOT updated rows.

  5. Introduce logical decoding.

  6. Fix bugs in SSI tuple locking.

  7. Implement genuine serializable isolation level.