== PostgreSQL Weekly News – April 29 2012 ==
== PostgreSQL Weekly News – April 29 2012 ==
== PostgreSQL Jobs for April ==
== PostgreSQL Local ==
PGCon 2012 will be held 17-18 May 2012, in Ottawa at the University of
Ottawa. It will be preceded by two days of tutorials on 15-16 May 2012.
PGDay France will be in Lyon on June 7, 2012.
PostgreSQL Conference Europe 2012 will be in Prague, Czech Republic
on October 23-26. The call for sponsors is open.
== PostgreSQL in the News ==
Planet PostgreSQL: http://planet.postgresql.org/
PostgreSQL Weekly News is brought to you this week by David Fetter
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== Reviews ==
== Applied Patches ==
Robert Haas pushed:
– Minor improvements for CHECK NO INHERIT documentation. Fix typo
spotted by Thom Brown, and improve wording in another area where
Thom spotted a typo.
– Reduce hash size for compute_array_stats, compute_tsvector_stats.
The size is only a hint, but a big hint chews up a lot of memory
without apparently improving performance much. Analysis and patch
by Noah Misch.
– Rearrange lazy_scan_heap to avoid visibility map race conditions.
We must set the visibility map bit before releasing our exclusive
lock on the heap page; otherwise, someone might clear the heap page
bit before we set the visibility map bit, leading to a situation
where the visibility map thinks the page is all-visible but it’s
really not. This problem has existed since 8.4, but it wasn’t
critical before we had index-only scans, since the worst case
scenario was that the page wouldn’t get vacuumed until the next
scan_all vacuum. Along the way, a couple of minor, related
improvements: (1) if we pause the heap scan to do an index vac
cycle, release any visibility map page we’re holding, since really
long-running pins are not good for a variety of reasons; and (2)
warn if we see a page that’s marked all-visible in the visibility
map but not on the page level, since that should never happen any
more (it was allowed in previous releases, but not in 9.2).
– Lots of doc corrections. Josh Kupershmidt
– Another typographical correction. Noted by Guillaume Smet.
– Casts to or from a domain type are ignored; warn and document.
Prohibiting this outright would break dumps taken from older
versions that contain such casts, which would create far more pain
than is justified here. Per report by Jaime Casanova and subsequent
– Remove prototype for nonexistent function.
– Prevent index-only scans from returning wrong answers under Hot
Standby. The alternative of disallowing index-only scans in HS
operation was discussed, but the consensus was that it was better to
treat marking a page all-visible as a recovery conflict for
snapshots that could still fail to see XIDs on that page. We may in
the future try to soften this, so that we simply force index scans
to do heap fetches in cases where this may be an issue, rather than
throwing a hard conflict.
Peter Eisentraut pushed:
– Fix minor stylistic issue
– entab: Improve makefile. A few simplifications and stylistic
improvements, found while grepping around for makefile problems
– Standardize indentation of XSL files. Predominant standard is two
spaces, so adjust outliers to that.
– PL/Python: Improve error messages
– psql: Tab completion updates. Add/complete support for: ALTER
DOMAIN / VALIDATE CONSTRAINT, ALTER DOMAIN / RENAME, ALTER DOMAIN /
RENAME CONSTRAINT, ALTER TABLE / RENAME CONSTRAINT,
– PL/Python: Accept strings in functions returning composite types..
Before 9.1, PL/Python functions returning composite types could
return a string and it would be parsed using record_in. The 9.1
changes made PL/Python only expect dictionaries, tuples, or objects
supporting getattr as output of composite functions, resulting in a
regression and a confusing error message, as the strings were
interpreted as sequences and the code for transforming lists to
database tuples was used. Fix this by treating strings separately
as before, before checking for the other types. The reason why it’s
important to support string to database tuple conversion is that
trigger functions on tables with composite columns get the composite
row passed in as a string (from record_out). Without supporting
converting this back using record_in, this makes it impossible to
implement pass-through behavior for these columns, as PL/Python no
longer accepts strings for composite values. A better solution
would be to fix the code that transforms composite inputs into
Python objects to produce dictionaries that would then be correctly
interpreted by the Python->PostgreSQL counterpart code. But that
would be too invasive to backpatch to 9.1, and it is too late in the
9.2 cycle to attempt it. It should be revisited in the future,
though. Reported as bug #6559 by Kirill Simonov. Jan Urbański
– PL/Python: Update list of supported environment variables
– Change return type of ExceptionalCondition to void and mark it
noreturn. In ancient times, it was thought that this wouldn’t work
because of TrapMacro/AssertMacro, but changing those to use a comma
operator appears to work without compiler warnings.
– Simplify makefile rule. Instead of writing out the .c -> .o rule,
use the default one, so that dependency tracking can be used.
Tom Lane pushed:
– Another trivial comment-typo fix.
– Fix edge-case behavior of pg_next_dst_boundary(). Due to rather
sloppy thinking (on my part, I’m afraid) about the appropriate
behavior for boundary conditions, pg_next_dst_boundary() gave
undefined, platform-dependent results when the input time is exactly
the last recorded DST transition time for the specified time zone,
as a result of fetching values one past the end of its data arrays.
Change its specification to be that it always finds the next DST
boundary *after* the input time, and adjust code to match that. The
sole existing caller, DetermineTimeZoneOffset, doesn’t actually care
about this distinction, since it always uses a probe time earlier
than the instant that it does care about. So it seemed best to me
to change the API to make the result=1 and result=0 cases more
consistent, specifically to ensure that the “before” outputs always
describe the state at the given time, rather than hacking the code
to obey the previous API comment exactly. Per bug #6605 from Sergey
Burladyan. Back-patch to all supported versions.
– Fix planner’s handling of RETURNING lists in writable CTEs.
setrefs.c failed to do “rtoffset” adjustment of Vars in RETURNING
lists, which meant they were left with the wrong varnos when the
RETURNING list was in a subquery. That was never possible before
writable CTEs, of course, but now it’s broken. The executor fails
to notice any problem because ExecEvalVar just references the
ecxt_scantuple for any normal varno; but EXPLAIN breaks when the
varno is wrong, as illustrated in a recent complaint from Bartosz
Dmytrak. Since the eventual rtoffset of the subquery is not known
at the time we are preparing its plan node, the previous scheme of
executing set_returning_clause_references() at that time cannot
handle this adjustment. Fortunately, it turns out that we don’t
really need to do it that way, because all the needed information is
available during normal setrefs.c execution; we just have to dig it
out of the ModifyTable node. So, do that, and get rid of the kluge
of early setrefs processing of RETURNING lists. (This is a little
bit of a cheat in the case of inherited UPDATE/DELETE, because we
are not passing a “root” struct that corresponds exactly to what the
subplan was built with. But that doesn’t matter, and anyway this is
less ugly than early setrefs processing was.) Back-patch to 9.1,
where the problem became possible to hit.
– Modify create_index regression test to avoid intermittent failures.
We have been seeing intermittent buildfarm failures due to a query
sometimes not using an index-only scan plan, because a background
auto-ANALYZE prevented the table’s all-visible bits from being set
immediately, thereby causing the estimated cost of an index-only
scan to go up considerably. Adjust the test case so that a bitmap
index scan is preferred instead, which serves equally well for the
purpose the test case is actually meant for. (Of course, it would
be better to eliminate the interference from auto-ANALYZE, but I see
no low-risk way to do that, so any such fix will have to be left for
9.3 or later.)
– Fix oversight in recent parameterized-path patch.
bitmap_scan_cost_est() has to be able to cope with a BitmapOrPath,
but I’d taken a shortcut that didn’t work for that case. Noted by
Heikki. Add some regression tests since this area is evidently
– Improve documentation around historical calendar rules. Get rid of
section 8.5.6 (Date/Time Internals), which appears to confuse people
more than it helps, and anyway discussion of Postgres’ internal
datetime calculation methods seems pretty out of place here.
Instead, make datatype.sgml just say that we follow the Gregorian
calendar (a bit of specification not previously present anywhere in
that chapter :-() and link to the History of Units appendix for more
info. Do some mild editorialization on that appendix, too, to make
it clearer that we are following proleptic Gregorian calendar rules
rather than anything more historically accurate. Per a question
from Florence Cousin and subsequent discussion in pgsql-docs.
– Fix syslogger’s rotation disable/re-enable logic. If it fails to
open a new log file, the syslogger assumes there’s something wrong
with its parameters (such as log_directory), and stops attempting
automatic time-based or size-based log file rotations. Sending it
SIGHUP is supposed to start that up again. However, the original
coding for that was really bogus, involving clobbering a couple of
GUC variables and hoping that SIGHUP processing would restore them.
Get rid of that technique in favor of maintaining a separate flag
showing we’ve turned rotation off. Per report from Mark Kirkwood.
Also, the syslogger will automatically attempt to create the
log_directory directory if it doesn’t exist, but that was only
happening at startup. For consistency and ease of use, it should do
the same whenever the value of log_directory is changed by SIGHUP.
Back-patch to all supported branches.
– Fix printing of whole-row Vars at top level of a SELECT targetlist.
Normally whole-row Vars are printed as “tabname.*”. However, that
does not work at top level of a targetlist, because per SQL standard
the parser will think that the “*” should result in column-by-column
expansion; which is not at all what a whole-row Var implies. We
used to just print the table name in such cases, which works most of
the time; but it fails if the table name matches a column name
available anywhere in the FROM clause. This could lead for instance
to a view being interpreted differently after dump and reload.
Adding parentheses doesn’t fix it, but there is a reasonably simple
kluge we can use instead: attach a no-op cast, so that the “*” isn’t
syntactically at top level anymore. This makes the printing of such
whole-row Vars a lot more consistent with other Vars, and may indeed
fix more cases than just the reported one; I’m suspicious that cases
involving schema qualification probably didn’t work properly before,
either. Per bug report and fix proposal from Abbas Butt, though
this patch is quite different in detail from his. Back-patch to all
– Clear I/O timing counters after sending them to the stats collector.
This oversight caused the reported times to accumulate in an O(N
fashion the longer a backend runs.
- Adjust timing units in pg_stat_statements. Display total time and
I/O timings in milliseconds, for consistency with the units used for
timings in the core statistics views. The columns remain of float8
type, so that sub-msec precision is available. (At some point we
will probably want to convert the core views to use float8 type for
the same reason, but this patch does not touch that issue.) This is
a release-note-requiring change in the meaning of the total_time
column. The I/O timing columns are new as of 9.2, so there is no
compatibility impact from redefining them. Do some minor
copy-editing in the documentation, too.
- Make a copy-editing pass over the new documentation for statistics
views. Fix a bunch of typos, improve markup, make wording more
uniform, rearrange some material. No substantive changes.
- Further editorialization on the new documentation for statistics
views. Get rid of the per-column documentation of underlying
functions, which did far more to clutter the view descriptions than
it did to be helpful, and was rather incomplete and typo-ridden
anyway. Instead suggest that people consult the definitions of the
standard views to see the underlying functions. The older functions
for obtaining individual facts about backends are now somewhat
obsoleted by pg_stat_get_activity, which means that they are not
documented by any standard view. So I put that information into a
separate table. (Maybe we should just deprecate them instead?) In
passing, fix a couple more documentation errors.
- Rename track_iotiming GUC to track_io_timing. This spelling seems
significantly more readable to me.
- Rename I/O timing statistics columns to blk_read_time and
blk_write_time. This seems more consistent with the pre-existing
choices for names of other statistics columns. Rename assorted
internal identifiers to match.
Bruce Momjian pushed:
- Add options to git_changelog for use in major release note creation:
--details-after --master-only --oldest-first
== Rejected Patches (for now) ==
No one was disappointed this week
== Pending Patches ==
Zoltan Boszormenyi sent in another version of the patches to create a
lock timeout framework and use same.
Alexander Korotkov sent in a patch to convert from pg_wchar to
multibyte, and Erik Rijkers followed up with some regression tests for
KaiGai Kohei sent in another revision of the patch to add generic
Noah Misch sent in a patch to fix an issue where psql does not include
a row count when auto-expanded output (\x auto) is set.
Kevin Grittner sent in a patch to fix an issue where setting
defautl_transaction_isolation to serializable (SSI) broke Hot
Robert Haas sent in a patch to modify "smart" shutdown mode to
disconnect sessions that are not in a transaction (or as soon as they
no longer are) but leaves in-progress transactions alone;
Noah Misch sent in a patch to allow TEMP tables on a hot standby.
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