Nouvelles hebdomadaires de PostgreSQL - 9 mars 2008
Les nouveautés des produits dérivés
Offres d'emplois autour de PostgreSQL en mars
http://archives.postgresql.org/pgsql-jobs/2008-03/threads.php
PostgreSQL Local
PostgreSQL dans les média
PostgreSQL Weekly News / les nouvelles hebdomadaires vous sont offertes cette semaine par David Fetter et Devrim Gunduz. La traduction en est assurée par l'équipe PostgreSQLFr.
Proposez vos articles ou annonces avant dimanche 15:00 (heure du Pacifique). Merci de les envoyer en anglais à david (a) fetter.org, en allemand à pwn (a) pgug.de, en italien à pwn (a) itpug.org.
Correctifs appliqués
Bruce Momjian a commité :
- 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 COPY FROM'"
- 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 table."
- 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 columns."
- 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 Singh.
- Break out referential integrity and server-side languages into separate TODO categories.
- Add to TODO: "Have CONSTRAINT cname NOT NULL preserve the contraint name."
- Move client encoding libpq function docs into libpq doc section, and just reference them from the localization doc section. Backpatch to 8.3.X.
- 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 backslashes."
- Add to TODO: "Reduce memory usage of aggregates in set returning functions."
- 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 8.3.X.
- 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 pg_class.reloptions."
- 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 words."
- 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 searches."
Magnus Hagander a commité :
- In pgsql/src/test/regress/pg_regress.c, use windows DACL fix for pg_regress as well. Dave Page
Tom Lane a commité :
- 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 own).
- 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 anyway.
- 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 section.
- 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 a commité :
- In pgsql/src/backend/port/dynloader/netbsd.c, clean up double negative, per Tom Lane.
Teodor Sigaev a commité :
- 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 Huxton.
- In pgsql/src/backend/utils/adt/tsquery_op.c, revert changes of CompareTSQ: it affects existing btree indexes.
Andrew Dunstan a commité :
- 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
Correctifs rejetés (à ce jour)
- 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 improvement.
Correctifs en attente
- 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 inheritance.
- 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 patch.
- Bryce Nesbitt sent in a patch which optionally sets a maximum width for psql output.