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== PostgreSQL Weekly News - August 10 2008 ==

From: David Fetter <david(at)fetter(dot)org>
To: PostgreSQL Announce <pgsql-announce(at)postgresql(dot)org>
Subject: == PostgreSQL Weekly News - August 10 2008 ==
Date: 2008-08-11 05:00:30
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-announce
== PostgreSQL Weekly News - August 10 2008 ==

== PostgreSQL Product News ==

BitNami LAPPStack 1.0 released.

pgbouncer 1.2.3 released.

phpPgAdmin 4.2.1 released.

PyReplica 1.0.3 released.

Another PostgreSQL Diff Tool 1.2 released.

pgSphere 1.0.1 released.

PostgreSQL Toolbox 1 released.

== PostgreSQL Jobs for August ==

== PostgreSQL Local ==

The Prato Linux User Group will be having PostgreSQL talks in
September.  The schedule in Italian is:

PGCon Brazil 2008 will be on September 26-27 at Unicamp in Campinas. will be October 4 in Toulouse.  The Call for Papers is open:

Sponsor the European PGDay!

The Call for Papers for European PGDay has begun.

PGDay.(IT|EU) 2008 will be October 17 and 18 in Prato.

== PostgreSQL in the News ==

Planet PostgreSQL:

General Bits, Archives and occasional new articles:

PostgreSQL Weekly News is brought to you this week by David Fetter and
Devrim GUNDUZ.

Submit news and announcements by Sunday at 3:00pm Pacific time.
Please send English language ones to david(at)fetter(dot)org, German language
to pwn(at)pgug(dot)de, Italian language to pwn(at)itpug(dot)org(dot)

== Applied Patches ==

Tom Lane committed:

- Improve CREATE/DROP/RENAME DATABASE so that when failing because the
  source or target database is being accessed by other users, it tells
  you whether the "other users" are live sessions or uncommitted
  prepared transactions.  (Indeed, it tells you exactly how many of
  each, but that's mostly just because it was easy to do so.)  This
  should help forestall the gotcha of not realizing that a prepared
  transaction is what's blocking the command.  Per discussion.

- Improve SELECT DISTINCT to consider hash aggregation, as well as
  sort/uniq, as methods for implementing the DISTINCT step.  This
  eliminates the former performance gap between DISTINCT and GROUP BY,
  and also makes it possible to do SELECT DISTINCT on datatypes that
  only support hashing not sorting.  SELECT DISTINCT ON is still
  always implemented by sorting; it would take executor changes to
  support hashing that, and it's not clear it's worth the trouble.
  This is a release-note-worthy incompatibility from previous PG
  versions, since SELECT DISTINCT can no longer be counted on to
  deliver sorted output without explicitly saying ORDER BY.  (Anyone
  who can't cope with that can consider turning off enable_hashagg.)
  Several regression test queries needed to have ORDER BY added to
  preserve stable output order.  I fixed the ones that manifested
  here, but there might be some other cases that show up on other

- In pgsql/src/test/regress/pg_regress.c, fix some message style
  guideline violations in pg_regress, as well as some failures to
  expose messages for translation.

- In pgsql/src/backend/storage/buffer/bufmgr.c, in ReadOrZeroBuffer
  (and related entry points), don't bother to call PageHeaderIsValid
  when we zero the buffer instead of reading the page in. The actual
  performance improvement is probably marginal since this function
  isn't very heavily used, but a cycle saved is a cycle earned Zdenek

- Add an ORDER BY to one more SELECT DISTINCT test case, per buildfarm

- In pgsql/src/backend/optimizer/plan/planner.c, department of second
  thoughts: fix newly-added code in planner.c to make real sure that
  DISTINCT ON does what it's supposed to, ie, sort by the full ORDER
  BY list before unique-ifying.  The error seems masked in simple
  cases by the fact that query_planner won't return query pathkeys
  that only partially match the requested sort order, but I wouldn't
  want to bet that it couldn't be exposed in some way or other.

- Do not allow Unique nodes to be scanned backwards.  The code claimed
  that it would work, but in fact it didn't return the same rows when
  moving backwards as when moving forwards.  This would have no
  visible effect in a DISTINCT query (at least assuming the column
  datatypes use a strong definition of equality), but it gave entirely
  wrong answers for DISTINCT ON queries.

- Teach the system how to use hashing for UNION.  (INTERSECT/EXCEPT
  will follow, but seem like a separate patch since most of the
  remaining work is on the executor side.)  I took the opportunity to
  push selection of the grouping operators for set operations into the
  parser where it belongs.  Otherwise this is just a small exercise in
  making prepunion.c consider both alternatives.  As with the recent
  DISTINCT patch, this means we can UNION on datatypes that can hash
  but not sort, and it means that UNION without ORDER BY is no longer
  certain to produce sorted output.

- Support hashing for duplicate-elimination in INTERSECT and EXCEPT
  queries.  This completes my project of improving usage of hashing
  for duplicate elimination (aggregate functions with DISTINCT remain
  undone, but that's for some other day).  As with the previous
  patches, this means we can INTERSECT/EXCEPT on datatypes that can
  hash but not sort, and it means that INTERSECT/EXCEPT without ORDER
  BY are no longer certain to produce sorted output.

- Improve INTERSECT/EXCEPT hashing by realizing that we don't need to
  make any hashtable entries for tuples that are found only in the
  second input: they can never contribute to the output.  Furthermore,
  this implies that the planner should endeavor to put first the
  smaller (in number of groups) input relation for an INTERSECT.
  Implement that, and upgrade prepunion's estimation of the number of
  rows returned by setops so that there's some amount of sanity in the
  estimate of which one is smaller.

- In pgsql/src/backend/executor/execMain.c, install checks in executor
  startup to ensure that the tuples produced by an INSERT or UPDATE
  will match the target table's current rowtype.  In pre-8.3 releases
  inconsistency can arise with stale cached plans, as reported by
  Merlin Moncure.  (We patched the equivalent hazard on the SELECT
  side in Feb 2007; I'm not sure why we thought there was no risk on
  the insertion side.) In 8.3 and HEAD this problem should be
  impossible due to plan cache invalidation management, but it seems
  prudent to make the check anyway.  Back-patch as far as 8.0.  7.x
  versions lack ALTER COLUMN TYPE, so there seems no way to abuse a
  stale plan comparably.

- Fix corner-case bug introduced with HOT: if REINDEX TABLE pg_class
  (or a REINDEX DATABASE including same) is done before a session has
  done any other update on pg_class, the pg_class relcache entry was
  left with an incorrect setting of rd_indexattr, because the
  indexed-attributes set would be first demanded at a time when we'd
  forced a partial list of indexes into the pg_class entry, and it
  would remain cached after that.  This could result in incorrect
  decisions about HOT-update safety later in the same session.  In
  practice, since only pg_class_relname_nsp_index would be missed out,
  problem.  Per report and test case from Ondrej Jirman.

Magnus Hagander committed:

- Move pgstat.tmp into a temporary directory under $PGDATA named
  pg_stat_tmp.  This allows the use of a ramdrive (either through
  mount or symlink) for the temporary file that's written every half
  second, which should reduce I/O.  On server shutdown/startup, the
  file is written to the old location in the global directory, to
  preserve data across restarts.  Bump catversion since the $PGDATA
  directory layout changed.

== Rejected Patches (for now) ==

No one was disappointed this week :-)

== Pending Patches ==

ITAGAKI Takahiro sent in a patch to user NDirectFileRead/Write
counters to get I/O counts in BufFile the module.  These counters are
visible when log_statement_stats is on.

Pavel Stehule sent in a patch to implement GROUPING SETS.

Tom Lane sent in a patch to use hashes for set operations.

Martin Pihlak sent in a patch to make dropping and re-creating
functions work more nicely with plan invalidation.

Simon Riggs sent in a patch which adds a hook for stats plugins.

Abhijit Menon-Sen sent in a patch which extend has_table_privilege()
to include sequence information.

Robert Haas sent in a patch to implement CREATE OR REPLACE VIEW.

Simon Riggs sent two revisions of a patch to fix pg_stop_backup per
suggestion by Fujii Masao.  pg_stop_backup now tests XLogArchiveCheckDone()
for both stopxlogfilename and history file and then stats the stop

Marko Kreen sent in a patch to fix a security issue in dblink.

Alvaro Herrera sent in two revisions of a patch to make autovacuum
process TOAST tables separately from main tables.

Volkan YAZICI sent in three revisions of a patch to allow people to
increase the verbosity of set-returning functions.

David Wheeler sent in some touch-ups for his citext patch.

Euler Taveira de Oliveira sent in a patch which allows symlinking
statistics files at initdb time.

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Subject: == PostgreSQL Weekly News - August 17 2008 ==
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