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Wöchentlicher PostgreSQL Newsletter - 09. März 2008

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== Wöchentlicher PostgreSQL Newsletter - 09. März 2008 ==

== PostgreSQL Produkt Neuigkeiten ==

Benetl 1.6 für Windows erschienen.

Continuent uni/cluster für PostgreSQL 2007.1 Update 2 erschienen.

Image2db 2.2 erschienen.

PL/Ruby 0.5.3 erschienen.

ptop 3.6.1 erschienen.

== PostgreSQL Jobs im März ==

== PostgreSQL Lokal ==

Der Call for Papers für die Utah Open Source Konferenz 2008 ist bis zum
1. Juni offen. Diese 2. jährliche Konferenz wird vom 28. bis 30. August
2008 in Salt Lake City, UT stattfinden.

Das erste Meeting der Atlanta PUG wird am 11. März 2008 um 18:30 Uhr

Das erste Meeting der Sun Coast PUG wird am 11. März 2008 sein.

Die LAPUG trifft sich am 28. März um 19:00 Uhr im City of Garden Grove

Der PG UK Tag wird am 2. April in Birmingham sein.

Der PG UK Tag wird am 2. April in Birmingham sein.

PostgreSQL Conference East '08 ist am 29. und 30. März an der
Universität von Maryland, College Park.

Die FISL wird vom 17. bis 19. April 2008 auf der PUCRS in Porto Alegre,
Brasilien, stattfinden.

== PostgreSQL in den News ==

Planet PostgreSQL:

General Bits, Archive und gelegentliche News Artikel:

Dieser wöchentliche PostgreSQL Newsletter wurde erstellt von David
Fetter and Devrim GUNDUZ.

Sende Neuigkeiten und Ankündigungen bis Sonntag, 15 Uhr Pazifischer
Zeit. Bitte sende englische Beiträge an, deutsche an, italienische an

== Angewandte Patches ==

Bruce Momjian committed:

- Add URL's for sequence discussions to TODO.

- Add information on (un)subscribing to mailing lists to the FAQ.

- Fix markup in FAQ.

- In pgsql/doc/src/sgml/func.sgml, document that the null byte is not
supported and explain why.

- In pgsql/doc/src/sgml/func.sgml, remove the word, "reliably" from
the above explanation.

- Add to TODO: "Speed WAL recovery by allowing more than one page to
be prefetched."

- Add to TODO: "Allow the UUID type to accept non-standard formats."

- In pgsql/doc/src/sgml/ref/revoke.sgml, document that REVOKE doesn't
remove all permissions if PUBLIC has permissions.

- Add to TODO: "Add another URL for: 'Consider using a ring buffer for

- Add to TODO: "Allow INSERT ... DELETE ... RETURNING, namely allow
the DELETE ... RETURNING to supply values to the INSERT"

- Update Japanese FAQ. Jun Kuwamura.

- Add to TODO: "ideas for concurrent pg_dump and pg_restore."

- Add URL for TODO: "Allow pg_restore to utilize multiple CPUs and I/O
channels by restoring multiple objects simultaneously."

- Remove TODO: "To better utilize resources, restore data, primary
keys, and indexes for a single table before restoring the next

- In pgsql/doc/src/sgml/textsearch.sgml, show example of ts_headline()
using a configuration name.

- Update TODO to read: "The difficulty with this is getting multiple
dump processes to produce a single dump output file. It also would
require several sessions to share the same snapshot."

- When text search string is too long, in error message report actual
and maximum number of bytes allowed.

- Add to TODO: "Allow COPY FROM to create index entries in bulk."

- Add URL for TODO: "Add SQL:2003 WITH RECURSIVE (hierarchical)
queries to SELECT."

- Add URL for TODO: "Add support for SQL-standard GENERATED/IDENTITY

- In pgsql/doc/src/sgml/config.sgml, document that increasing the
number of checkpoints segments or checkpoint timeout can incrase the
time needed for crash recovery, per suggestion from Simon Riggs.

- In pgsql/README, update libpqxx URL in top-level README, per Gurjeet

- Break out referential integrity and server-side languages into
separate TODO categories.

- Add to TODO: "Have CONSTRAINT cname NOT NULL preserve the contraint

- Move client encoding libpq function docs into libpq doc section, and
just reference them from the localization doc section. Backpatch to

- In pgsql/src/backend/utils/misc/guc.c, improve
"bgwriter_lru_multiplier" GUC description.

- Add to TODO: "Prevent malicious functions from being executed with
the permissions of unsuspecting users."

- Add to TODO: "Prevent escape string warnings when object names have

- Add to TODO: "Reduce memory usage of aggregates in set returning

- Document use of pg_locks.objid for advisory locks, suggestion from
Marc Mamin.

- Add to TODO: "Allow client certificate names to be checked against
the client hostname."

- In pgsql/doc/src/sgml/installation.sgml, document that enabling
asserts can significantly slow down the server. Back patch to

- Add URL for TODO: "Add SQL:2003 WITH RECURSIVE (hierarchical)
queries to SELECT."

- Add URL for TODO: "Consider compressing indexes by storing key
values duplicated in several rows as a single index entry."

- Add to TODO: "Have \d show foreign keys that reference a table's
primary key." and "Have \d show child tables that inherit from the
specified parent."

- Add to TODO: "Require all CHECK constraints to be inherited."

- In pgsql/doc/src/sgml/backup.sgml, clarify PITR doc wording.

- Add to TODO: "Add comments on system tables/columns using the
information in catalogs.sgml."

- Add to TODO: "Have \l+ show database size, if permissions allow."

- Add to TODO: "Add SQLSTATE severity to PGconn return status."

- Add URL for TODO: "Allow multiple identical NOTIFY events to always
be communicated to the client, rather than sent as a single
notification to the listener."

- Add to TODO: "Store per-table autovacuum settings in

- Add to TODO: "Improve referential integrity checks."

- Add to TODO: "Consider allowing higher priority queries to have
referenced buffer cache pages stay in memory longer."

- Add to TODO: "Allow text search dictionary to filter out only stop

- Add to TODO: "Prevent autovacuum from running if an old transaction
is still running from the last vacuum."

- Add to TODO: "Add a function like pg_get_indexdef() that report more
detailed index information."

- Add to TODO: "Consider a function-based API for '@@' full text

Magnus Hagander committed:

- In pgsql/src/test/regress/pg_regress.c, use windows DACL fix for
pg_regress as well. Dave Page

Tom Lane committed:

- Fix PREPARE TRANSACTION to reject the case where the transaction has
dropped a temporary table; we can't support that because there's no
way to clean up the source backend's internal state if the eventual
COMMIT PREPARED is done by another backend. This was checked
correctly in 8.1 but I broke it in 8.2 :-(. Patch by Heikki
Linnakangas, original trouble report by John Smith.

- In pgsql/src/interfaces/libpq/Makefile, include -lgss in libpq link,
if available. Bjorn Munch.

- In pgsql/src/backend/utils/cache/catcache.c, in
PrepareToInvalidateCacheTuple, don't force initialization of catalog
caches that we don't actually need to touch. This saves some
trivial number of cycles and avoids certain cases of deadlock when
doing concurrent VACUUM FULL on system catalogs. Per report from
Gavin Roy. Backpatch to 8.2. In earlier versions,
CatalogCacheInitializeCache didn't lock the relation so there's no
deadlock risk (though that certainly had plenty of risks of its

- In pgsql/src/backend/access/hash/hashscan.c, change hashscan.c to
keep its list of active hash index scans in TopMemoryContext, rather
than scattered through executor per-query contexts. This poses no
danger of memory leak since the ResourceOwner mechanism guarantees
release of no-longer-needed items. It is needed because the
per-query context might already be released by the time we try to
clean up the hash scan list. Report by ykhuang, diagnosis by
Heikki. Back-patch to 8.0, where the ResourceOwner-based cleanup
was introduced. The given test case does not fail before 8.2,
probably because we rearranged transaction abort processing somehow;
but this coding is undoubtedly risky so I'll patch 8.0 and 8.1

- This patch addresses some issues in TOAST compression strategy that
were discussed last year, but we felt it was too late in the 8.3
cycle to change the code immediately. Specifically, the patch:
Reduces the minimum datum size to be considered for compression from
256 to 32 bytes, as suggested by Greg Stark. Increases the required
compression rate for compressed storage from 20% to 25%, again per
Greg's suggestion. Replaces force_input_size (size above which
compression is forced) with a maximum size to be considered for
compression. It was agreed that allowing large inputs to escape the
minimum-compression-rate requirement was not bright, and that indeed
we'd rather have a knob that acted in the other direction. I set
this value to 1MB for the moment, but it could use some performance
studies to tune it. Adds an early-failure path to the compressor as
suggested by Jan: if it's been unable to find even one compressible
substring in the first 1KB (parameterizable), assume we're looking
at incompressible input and give up. (Possibly this logic can be
improved, but I'll commit it as-is for now.) Improves the toasting
heuristics so that when we have very large fields with attstorage
'x' or 'e', we will push those out to toast storage before
considering inline compression of shorter fields. This also
responds to a suggestion of Greg's, though my original proposal for
a solution was a bit off base because it didn't fix the problem for
large 'e' fields. There was some discussion in the earlier threads
of exposing some of the compression knobs to users, perhaps even on
a per-column basis. I have not done anything about that here. It
seems to me that if we are changing around the parameters, we'd
better get some experience and be sure we are happy with the design
before we set things in stone by providing user-visible knobs.

- Improve pglz_decompress() so that it cannot clobber memory beyond
the available output buffer when presented with corrupt input. Some
testing suggests that this slows the decompression loop about 1%,
which seems an acceptable price to pay for more robustness.
(Curiously, the penalty seems to be less on not-very-compressible
data, which I didn't expect since the overhead per output byte ought
to be more in the literal-bytes path.) Patch from Zdenek Kotala. I
fixed a corner case and did some renaming of variables to make the
routine more readable.

- Refactor heap_page_prune so that instead of changing item states
on-the-fly, it accumulates the set of changes to be made and then
applies them. It had to accumulate the set of changes anyway to
prepare a WAL record for the pruning action, so this isn't an
enormous change; the only new complexity is to not doubly mark
tuples that are visited twice in the scan. The main advantage is
that we can substantially reduce the scope of the critical section
in which the changes are applied, thus avoiding PANIC in foreseeable
cases like running out of memory in inval.c. A nice secondary
advantage is that it is now far clearer that WAL replay will
actually do the same thing that the original pruning did. This
commit doesn't do anything about the open problem that
CacheInvalidateHeapTuple doesn't have the right semantics for a CTID
change caused by collapsing out a redirect pointer. But whatever we
do about that, it'll be a good idea to not do it inside a critical

- Modify prefix_selectivity() so that it will never estimate the
selectivity of the generated range condition var >= 'foo' AND var <
'fop' as being less than what eqsel() would estimate for var =
'foo'. This is intuitively reasonable and it gets rid of the need
for some entirely ad-hoc coding we formerly used to reject bogus
estimates. The basic problem here is that if the prefix is more
than a few characters long, the two boundary values are too close
together to be distinguishable by comparison to the column
histogram, resulting in a selectivity estimate of zero, which is
often not very sane. Change motivated by an example from Peter
Eisentraut. Arguably this is a bug fix, but I'll refrain from
back-patching it for the moment.

- Change patternsel() so that instead of switching from a pure
pattern-examination heuristic method to purely histogram-driven
selectivity at histogram size 100, we compute both estimates and use
a weighted average. The weight put on the heuristic estimate
decreases linearly with histogram size, dropping to zero for 100 or
more histogram entries. Likewise in ltreeparentsel(). After a
patch by Greg Stark, though I reorganized the logic a bit to give
the caller of histogram_selectivity() more control.

- Remove postmaster.c's check that NBuffers is at least twice
MaxBackends. With the addition of multiple autovacuum workers, our
choices were to delete the check, document the interaction with
autovacuum_max_workers, or complicate the check to try to hide that
interaction. Since this restriction has never been adequate to
ensure backends can't run out of pinnable buffers, it doesn't really
have enough excuse to live to justify the second or third choices.
Per discussion of a complaint from Andreas Kling (see also bug
#3888). This commit also removes several documentation references
to this restriction, but I'm not sure I got them all.

Alvaro Herrera committed:

- In pgsql/src/backend/port/dynloader/netbsd.c, clean up double
negative, per Tom Lane.

Teodor Sigaev committed:

- In pgsql/src/backend/tsearch/to_tsany.c, fix memory arrangement of
tsquery after removing stop words. It causes a unused memory holes
in tsquery. It had been working because tsquery->size was not used
for any kind of operation except comparing tsqueries, so in HEAD
it's enough to fix to_tsquery function, but for previous versions
it's necessary to remove the optimization in CompareTSQ to prevent
requirement of renewing all stored tsquerys. Per report by Richard

- In pgsql/src/backend/utils/adt/tsquery_op.c, revert changes of
CompareTSQ: it affects existing btree indexes.

Andrew Dunstan committed:

- In pgsql/src/backend/commands/copy.c, improve efficiency of
attribute scanning in CopyReadAttributesCSV. The loop is split into
two parts, inside quotes, and outside quotes, saving some
instructions in both parts. Heikki Linnakangas

== Abgelehnte Patches (bis jetzt) ==

Marko Kreen's patch of November 23, 2007 which moved the decision
about how much more room to allocate from callers of
appendStringInfoVA isnide the function, where more information is
available, on grounds of unportability and dubious performance

== Eingesandte Patches ==

Kenneth D'Souza sent in another revision of his patch to psql which
shows incoming foreign key constraints along with the existing
out-going foreign key constraints when people invoke \d table_name.

Alex Hunsaker sent in a patch intended to fix a bug in ALTER TABLE
which allows dropping a NOT NULL constraint in places where it breaks

Magnus Hagander sent in a WIP patch to make GUC enums.

Zoltan Boszormenyi sent in two revisions of a patch to allow for
64-bit CommandIds.

Pavel Stehule sent in an updated SQL/PSM patch.

Julius Stroffek sent in a patch intended to allow people to use Sun's
compiler to compile Postgres on Linux.

Bruce Momjian sent in a patch to clarify an error message for the
tsvector cast when the string is too long.

Merlin Moncure sent in another revision of his libpq type system

Bryce Nesbitt sent in a patch which optionally sets a maximum width
for psql output.


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