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Postgres FD Implementation
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  1. 10 Apr, 2021 2 commits
  3. 09 Apr, 2021 9 commits
  5. 08 Apr, 2021 24 commits
  7. 07 Apr, 2021 5 commits
    • Peter Geoghegan's avatar
      Teach VACUUM to bypass unnecessary index vacuuming. · 5100010e
      Peter Geoghegan authored 
      VACUUM has never needed to call ambulkdelete() for each index in cases
where there are precisely zero TIDs in its dead_tuples array by the end
of its first pass over the heap (also its only pass over the heap in
this scenario).  Index vacuuming is simply not required when this
happens.  Index cleanup will still go ahead, but in practice most calls
to amvacuumcleanup() are usually no-ops when there were zero preceding
ambulkdelete() calls.  In short, VACUUM has generally managed to avoid
index scans when there were clearly no index tuples to delete from
indexes.  But cases with _close to_ no index tuples to delete were
another matter -- a round of ambulkdelete() calls took place (one per
index), each of which performed a full index scan.

VACUUM now behaves just as if there were zero index tuples to delete in
cases where there are in fact "virtually zero" such tuples.  That is, it
can now bypass index vacuuming and heap vacuuming as an optimization
(though not index cleanup).  Whether or not VACUUM bypasses indexes is
determined dynamically, based on the just-observed number of heap pages
in the table that have one or more LP_DEAD items (LP_DEAD items in heap
pages have a 1:1 correspondence with index tuples that still need to be
deleted from each index in the worst case).

We only skip index vacuuming when 2% or less of the table's pages have
one or more LP_DEAD items -- bypassing index vacuuming as an
optimization must not noticeably impede setting bits in the visibility
map.  As a further condition, the dead_tuples array (i.e. VACUUM's array
of LP_DEAD item TIDs) must not exceed 32MB at the point that the first
pass over the heap finishes, which is also when the decision to bypass
is made.  (The VACUUM must also have been able to fit all TIDs in its
maintenance_work_mem-bound dead_tuples space, though with a default
maintenance_work_mem setting it can't matter.)

This avoids surprising jumps in the duration and overhead of routine
vacuuming with workloads where successive VACUUM operations consistently
have almost zero dead index tuples.  The number of LP_DEAD items may
well accumulate over multiple VACUUM operations, before finally the
threshold is crossed and VACUUM performs conventional index vacuuming.
Even then, the optimization will have avoided a great deal of largely
unnecessary index vacuuming.

In the future we may teach VACUUM to skip index vacuuming on a per-index
basis, using a much more sophisticated approach.  For now we only
consider the extreme cases, where we can be quite confident that index
vacuuming just isn't worth it using simple heuristics.

Also log information about how many heap pages have one or more LP_DEAD
items when autovacuum logging is enabled.

Author: Masahiko Sawada <sawada.mshk@gmail.com>
Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAD21AoD0SkE11fMw4jD4RENAwBMcw1wasVnwpJVw3tVqPOQgAw@mail.gmail.com
Discussion: https://postgr.es/m/CAH2-WzmkebqPd4MVGuPTOS9bMFvp9MDs5cRTCOsv1rQJ3jCbXw@mail.gmail.com
      5100010e
    • Bruce Momjian's avatar
      Fix regression test failure caused by commit 4f0b0966 · bc707286
      Bruce Momjian authored 
      The query originally used was too simple, cause explain_filter() to be
unable to remove JIT output text.

Reported-by: Tom Lane

Author: Julien Rouhaud
      bc707286
    • Michael Paquier's avatar
      Fix some failures with connection tests on Windows hosts · c7578fa6
      Michael Paquier authored 
      The truncation of the log file, that this set of tests relies on to make
sure that a connection attempt matches with its expected backend log
pattern, fails, as reported by buildfarm member fairywren.  Instead of a
truncation, do a rotation of the log file and restart the node.  This
will ensure that the connection attempt data is unique for each test.

Discussion: https://postgr.es/m/YG05nCI8x8B+Ad3G@paquier.xyz
      c7578fa6
    • Peter Eisentraut's avatar
      SQL-standard function body · e717a9a1
      Peter Eisentraut authored 
      This adds support for writing CREATE FUNCTION and CREATE PROCEDURE
statements for language SQL with a function body that conforms to the
SQL standard and is portable to other implementations.

Instead of the PostgreSQL-specific AS $$ string literal $$ syntax,
this allows writing out the SQL statements making up the body
unquoted, either as a single statement:

    CREATE FUNCTION add(a integer, b integer) RETURNS integer
        LANGUAGE SQL
        RETURN a + b;

or as a block

    CREATE PROCEDURE insert_data(a integer, b integer)
    LANGUAGE SQL
    BEGIN ATOMIC
      INSERT INTO tbl VALUES (a);
      INSERT INTO tbl VALUES (b);
    END;

The function body is parsed at function definition time and stored as
expression nodes in a new pg_proc column prosqlbody.  So at run time,
no further parsing is required.

However, this form does not support polymorphic arguments, because
there is no more parse analysis done at call time.

Dependencies between the function and the objects it uses are fully
tracked.

A new RETURN statement is introduced.  This can only be used inside
function bodies.  Internally, it is treated much like a SELECT
statement.

psql needs some new intelligence to keep track of function body
boundaries so that it doesn't send off statements when it sees
semicolons that are inside a function body.
Tested-by: default avatarJaime Casanova <jcasanov@systemguards.com.ec>
Reviewed-by: default avatarJulien Rouhaud <rjuju123@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/1c11f1eb-f00c-43b7-799d-2d44132c02d7@2ndquadrant.com
      e717a9a1
    • Peter Geoghegan's avatar
      Add wraparound failsafe to VACUUM. · 1e55e7d1
      Peter Geoghegan authored 
      Add a failsafe mechanism that is triggered by VACUUM when it notices
that the table's relfrozenxid and/or relminmxid are dangerously far in
the past.  VACUUM checks the age of the table dynamically, at regular
intervals.

When the failsafe triggers, VACUUM takes extraordinary measures to
finish as quickly as possible so that relfrozenxid and/or relminmxid can
be advanced.  VACUUM will stop applying any cost-based delay that may be
in effect.  VACUUM will also bypass any further index vacuuming and heap
vacuuming -- it only completes whatever remaining pruning and freezing
is required.  Bypassing index/heap vacuuming is enabled by commit
8523492d, which made it possible to dynamically trigger the mechanism
already used within VACUUM when it is run with INDEX_CLEANUP off.

It is expected that the failsafe will almost always trigger within an
autovacuum to prevent wraparound, long after the autovacuum began.
However, the failsafe mechanism can trigger in any VACUUM operation.
Even in a non-aggressive VACUUM, where we're likely to not advance
relfrozenxid, it still seems like a good idea to finish off remaining
pruning and freezing.   An aggressive/anti-wraparound VACUUM will be
launched immediately afterwards.  Note that the anti-wraparound VACUUM
that follows will itself trigger the failsafe, usually before it even
begins its first (and only) pass over the heap.

The failsafe is controlled by two new GUCs: vacuum_failsafe_age, and
vacuum_multixact_failsafe_age.  There are no equivalent reloptions,
since that isn't expected to be useful.  The GUCs have rather high
defaults (both default to 1.6 billion), and are expected to generally
only be used to make the failsafe trigger sooner/more frequently.

Author: Masahiko Sawada <sawada.mshk@gmail.com>
Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAD21AoD0SkE11fMw4jD4RENAwBMcw1wasVnwpJVw3tVqPOQgAw@mail.gmail.com
Discussion: https://postgr.es/m/CAH2-WzmgH3ySGYeC-m-eOBsa2=sDwa292-CFghV4rESYo39FsQ@mail.gmail.com
      1e55e7d1