== PostgreSQL Weekly News - June 10 2007 ==

== PostgreSQL Weekly News - June 10 2007 ==

Michael Glaesemann's photographs from PGCon 2007 are now online at
http://flickr.com/photos/grzm/sets/72157600270827416/.  The photos are
tagged "pgcon" and "pgcon2007".  If you've posted photos from the
conference, you're encouraged to do the same to make them more
conveniently found.  If you happen to find any errors in captioning or
tagging, please let Michael know at grzm [at] seespotcode [dot] net.
Enjoy the photos!

== PostgreSQL Product News ==

Archiveopteryx 2.0 released.
http://www.archiveopteryx.org/2.0.html

PostgreSQL tablelog 0.4.4 released.
http://pgfoundry.org/projects/tablelog/

== PostgreSQL Jobs for June ==

http://archives.postgresql.org/pgsql-jobs/2007-06/threads.php

== PostgreSQL Local ==

SFPUG's next meeting is Tuesday, June 12 at Hi5 in San Francisco.
Details below.  RSVP for free food.
http://postgresql.meetup.com/1/calendar/5808330/

Registration for pgday.it in Prato, Tuscany, Italy on July 6 and 7 is
open.

Some Important URLs:

Registration: http://www.pgday.it/en/generale/registrazione
PGDay's web site: http://www.pgday.it/en/
Sponsorship campaign: http://www.pgday.it/en/sponsorizzazioni/come
How to get to Prato: http://www.pgday.it/en/logistica/raggiungere_prato
Accommodations in Prato: http://www.pgday.it/en/logistica/dove_dormire
PostgreSQL official T-shirts http://www.prato.linux.it/node/30
Sign up to tour Tuscany: http://www.pgday.it/it/node/158

Important dates:

May 31: Deadline for the call for papers
June 5: Special accommodation rates expire for Hotel San Marco and Art Hotel Milano

== PostgreSQL in the News ==

Planet PostgreSQL: http://www.planetpostgresql.org/

General Bits, Archives and occasional new articles:
http://www.varlena.com/GeneralBits/

PostgreSQL Weekly News is brought to you this week by David Fetter

To get your submission into the upcoming issue, make sure it arrives
at david@fetter.org or in German at pwn@pgug.de by Sunday at 3:00pm
Pacific Time.

== Applied Patches ==

Bruce Momjian committed:

- Mark TODO as DONE: "Allow UPDATE/DELETE WHERE CURRENT OF cursor."

- Mark TODO as DONE: "Allow sequential scans to take advantage of
  other concurrent sequential scans, also called 'Synchronised
  Scanning'"

Alvaro Herrera committed:

- Disallow the cost balancing code from resulting in a zero cost
  limit, which causes a division-by-zero error in the vacuum code.
  This can happen when there are more workers than cost limit units.
  Per report from Galy Lee.

- Avoid passing zero as a value for vacuum_cost_limit, because it's
  not a valid value for the vacuum code.  Instead, make zero signify
  getting the value from a higher level configuration facility, just
  like -1 in the original coding.  We still document that -1 is the
  value that disables the feature, to avoid confusing the user
  unnecessarily.  Reported by Galy Lee, per subsequent discussion.

- Avoid losing track of data for shared tables in pgstats.  Report by
  Michael Fuhr, patch from Tom Lane after a messier suggestion by me.

Magnus Hagander committed:

- ITAGAKI Takahiro's patch which changes the Japanese docs in
  contrib/pgstattuple to reflect the fact that the functions bt_metap,
  bt_page_stats and bt_page_items have moved from there to
  pageinspect.

Jan Wieck committed:

- The session_replication_role actually can be changed at will during
  a session regardless of the existence of cached plans.  The
  plancache only needs to be invalidated so that rules affected by the
  new setting will be reflected in the new query plans.

Teodor Sigaev committed:

- Move call of MarkBufferDirty() before XLogInsert() as required.
  Many thanks to Heikki Linnakangas <heikki@enterprisedb.com> for his
  sharp eyes.

- Replace ReadBuffer to ReadBufferWithStrategy in all vacuum-involved
  places to implement limited-size "ring" of buffers for VACUUM for
  GIN & GIST.

Tom Lane committed:

- Support UPDATE/DELETE WHERE CURRENT OF cursor_name, per SQL
  standard.  Along the way, allow FOR UPDATE in non-WITH-HOLD cursors;
  there may once have been a reason to disallow that, but it seems to
  work now, and it's really rather necessary if you want to select a
  row via a cursor and then update it in a concurrent-safe fashion.
  Original patch by Arul Shaji, rather heavily editorialized by Tom
  Lane.

- Teach heapam code to know the difference between a real seqscan and
  the pseudo HeapScanDesc created for a bitmap heap scan.  This avoids
  some useless overhead during a bitmap scan startup, in particular
  invoking the syncscan code.  (We might someday want to do that, but
  right now it's merely useless contention for shared memory, to say
  nothing of possibly pushing useful entries out of syncscan's small
  LRU list.)  This also allows elimination of ugly
  pgstat_discount_heap_scan() kluge.

- Insert ORDER BY into a few regression test queries that now have
  unstable results due to syncscan patch, when shared_buffers is small
  enough.  Per buildfarm reports and some local testing with
  shared_buffers set to the lowest value considered by initdb.

- Allow numeric_fac() to be interrupted, since it can take quite a
  while for large inputs.  Also cause it to error out immediately if
  the result will overflow, instead of grinding through a lot of
  calculation first.  Per gripe from Jim Nasby.

- Add note that LIMIT without ORDER BY can produce outright
  nondeterministic results.  Necessary due to introduction of syncscan
  patch.

- Arrange for large sequential scans to synchronize with each other,
  so that when multiple backends are scanning the same relation
  concurrently, each page is (ideally) read only once.  Jeff Davis,
  with review by Heikki and Tom.

- Redefine IsTransactionState() to only return true for
  TRANS_INPROGRESS state, which is the only state in which it's safe
  to initiate database queries.  It turns out that all but two of the
  callers thought that's what it meant; and the other two were using
  it as a proxy for "will GetTopTransactionId() return a nonzero XID"?
  Since it was in fact an unreliable guide to that, make those two
  just invoke GetTopTransactionId() always, then deal with a zero
  result if they get one.

- Rework temp_tablespaces patch so that temp tablespaces are assigned
  separately for each temp file, rather than once per sort or
  hashjoin; this allows spreading the data of a large sort or join
  across multiple tablespaces.  (I remain dubious that this will make
  any difference in practice, but certain people insisted.)  Arrange
  to cache the results of parsing the GUC variable instead of
  recomputing from scratch on every demand, and push usage of the
  cache down to the bottommost fd.c level.

- Christian Rossow's patch which fixes array_dims() example to be
  consistent with the data previously shown.

- Fix up text concatenation so that it accepts all the reasonable
  cases that were accepted by prior Postgres releases.  This takes
  care of the loose end left by the preceding patch to downgrade
  implicit casts-to-text.  To avoid breaking desirable behavior for
  array concatenation, introduce a new polymorphic pseudo-type
  "anynonarray" --- the added concatenation operators are actually
  text || anynonarray and anynonarray || text.

- Minor editorialization: don't flush plan cache without need.

- Downgrade implicit casts to text to be assignment-only, except for
  the ones from the other string-category types; this eliminates a lot
  of surprising interpretations that the parser could formerly make
  when there was no directly applicable operator.  Create a general
  mechanism that supports casts to and from the standard string types
  (text,varchar,bpchar) for *every* datatype, by invoking the
  datatype's I/O functions.  These new casts are assignment-only in
  the to-string direction, explicit-only in the other, and therefore
  should create no surprising behavior.  Remove a bunch of
  thereby-obsoleted datatype-specific casting functions.  The "general
  mechanism" is a new expression node type CoerceViaIO that can
  actually convert between *any* two datatypes if their external text
  representations are compatible.  This is more general than needed
  for the immediate feature, but might be useful in plpgsql or other
  places in future.  This commit does nothing about the issue that
  applying the concatenation operator || to non-text types will now
  fail, often with strange error messages due to misinterpreting the
  operator as array concatenation.  Since it often (not always) worked
  before, we should either make it succeed or at least give a more
  user-friendly error; but details are still under debate.  Peter
  Eisentraut and Tom Lane

== Rejected Patches (for now) ==

No one was disappointed this week :-)

== Pending Patches ==

Andrew Dunstan sent in a WIP patch for CSV logs.

Simon Riggs sent in a patch to fix recent PITR bug, with proposals as
discussed on -admin and -hackers.  Patch implements option #3, as
proposed here:
http://archives.postgresql.org/pgsql-hackers/2007-06/msg00234.php

Magnus Hagander sent in another revision of Joachim Wieland's patch
which changes some regression tests for ECPG.