Horton

Re: Pluggable Storage - Andres's take

Dmitry Dolgov <9erthalion6@gmail.com>

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From: Dmitry Dolgov <9erthalion6@gmail.com>
To: Haribabu Kommi <kommi.haribabu@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Alvaro Herrera <alvherre@2ndquadrant.com>, Alexander Korotkov <a.korotkov@postgrespro.ru>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-10-31T10:34:59Z
Lists: pgsql-hackers 
> On Mon, 29 Oct 2018 at 05:56, Haribabu Kommi <kommi.haribabu@gmail.com> wrote:
>
>> This problem couldn't be reproduced on the master branch, so I've tried to
>> investigate it. It comes from nodeModifyTable.c:1267, when we've got
>> HeapTupleInvisible as a result, and this value in turn comes from
>> table_lock_tuple. Everything points to the new way of handling HeapTupleUpdated
>> result from heap_update, when table_lock_tuple call was introduced. Since I
>> don't see anything similar in the master branch, can anyone clarify why is this
>> lock necessary here?
>
>
> In the master branch code also, there is a tuple lock that is happening in
> EvalPlanQual() function, but pluggable-storage code, the lock is kept outside
> and also function call rearrangements, to make it easier for the table access
> methods to provide their own MVCC implementation.

Yes, now I see it, thanks. Also I can confirm that the attached patch solves
this issue.

FYI, alongside with reviewing the code changes I've ran few performance tests
(that's why I hit this issue with pgbench in the first place). In case of high
concurrecy so far I see small performance degradation in comparison with the
master branch (about 2-5% of average latency, depending on the level of
concurrency), but can't really say why exactly (perf just shows barely
noticeable overhead there and there, maybe what I see is actually a cumulative
impact).

Commits

  1. Add default_table_access_method to postgresql.conf.sample.

  2. tableam: Avoid relying on relation size to determine validity of tids.

  3. tableam: Don't assume that every AM uses md.c style storage.

  4. Allow pg_class xid & multixid horizons to not be set.

  5. Fix slot type issue for fuzzy distance index scan over out-of-core table AM.

  6. tableam: comment and formatting fixes.

  7. table: docs: fix typos and grammar.

  8. tableam: basic documentation.

  9. Only allow heap in a number of contrib modules.

  10. tableam: Add table_finish_bulk_insert().

  11. tableam: sample scan.

  12. tableam: bitmap table scan.

  13. tableam: Move heap specific logic from estimate_rel_size below tableam.

  14. tableam: VACUUM and ANALYZE support.

  15. tableam: relation creation, VACUUM FULL/CLUSTER, SET TABLESPACE.

  16. tableam: Support for an index build's initial table scan(s).

  17. tableam: Add table_get_latest_tid, to wrap heap_get_latest_tid.

  18. tableam: Add helper for indexes to check if a corresponding table tuples exist.

  19. tableam: Add and use table_fetch_row_version().

  20. tableam: Use in CREATE TABLE AS and CREATE MATERIALIZED VIEW.

  21. Ensure sufficient alignment for ParallelTableScanDescData in BTShared.

  22. Don't reuse slots between root and partition in ON CONFLICT ... UPDATE.

  23. Use a virtual rather than a heap slot in two places where that suffices.

  24. Store tuples for EvalPlanQual in slots, rather than as HeapTuples.

  25. Use slots in trigger infrastructure, except for the actual invocation.

  26. Store table oid and tuple's tid in tuple slots directly.

  27. Allow to use HeapTupleData embedded in [Buffer]HeapTupleTableSlot.

  28. Add ExecStorePinnedBufferHeapTuple.

  29. Add ArchiveOpts to pass options to ArchiveEntry

  30. Rename RelationData.rd_amroutine to rd_indam.

  31. Rephrase references to "time qualification".

  32. Move remaining code from tqual.[ch] to heapam.h / heapam_visibility.c.

  33. Move generic snapshot related code from tqual.h to snapmgr.h.

  34. Remove superfluous tqual.h includes.

  35. Don't duplicate parallel seqscan shmem sizing logic in nbtree.

  36. Move vacuumlazy.c into access/heap.

  37. Support parallel bitmap heap scans.