Notiziario settimanale PostgreSQL – 9 maggio 2009

(Traduzione parziale in lingua italiana delle PostgreSQL Weekly News a cura di Gianni Ciolli gianni.ciolli@2ndquadrant.it)

Nuovo sondaggio: quale ti emoziona di più tra le caratteristiche della 8.4? www.postgresql.org/community

Il sito web di PostgreSQL ha bisogno di una manutenzione, per la quale sono stati stanziati $2000. La tua abilità può farti ottenere la fama, e una (piccola) fortuna. http://wiki.postgresql.org/wiki/Website_Overhaul_Requirements

Il PGDay Junin / Buenos Aires Unnoba si terrà il 6 giugno 2009. http://www.arpug.com.ar/trac/wiki/PgDayUnnoba

Il PGDay.EU 2009 si terrà a Telecom ParisTech in Parigi nei giorni 6 e 7 novembre 2009. http://www.pgday.eu/

Novità sul prodotto PostgreSQL

Rilasciata la versione 2.8.0 di check_postgres, un plug-in Nagios per il monitoraggio di PostgreSQL. http://bucardo.org/check_postgres/

Rilasciata la versione 2.2 di Jopr, una applicazione per gestione e monitoraggio di server. http://www.jboss.org/jopr/

Il progetto PostgreSQL RPM Building ha rilasciato una nuova versione del CD Live PostgreSQL. http://www.pglivecd.org

Rilasciata la versione 2.0.5 di Npgsql2, un provider di dati .NET per PostgreSQL. http://www.npgsql.org

Rilasciata la versione 1.10 beta 3 di pgAdmin, uno strumento GUI di gestione per PostgreSQL. http://www.postgresql.org/ftp/pgadmin3/release/v1.10.0-beta3/

Rilasciata la versione 2.2.2 di pgpool-II, un connection pooler (e non solo). http://pgfoundry.org/projects/pgpool/

La United States PostgreSQL Association è adesso una associazione non-profit 501(c)(3). Complimenti! http://www.postgresql.us/

Rilasciata la versione 1.3.6 di PostGIS, un sistema geospaziale per PostgreSQL. http://postgis.refractions.net/

Rilasciate le versioni 1.2.16 e 2.0.2 di Slony, un sistema di replica master-slave a cascata per PostgreSQL. http://slony.info/

La novità della settimana di PostgreSQL 8.4

Le funzioni Windowing. Le query di report sono diventate estremamente più facili. In questo caso è particolarmente utile PARTITION BY.

Il suggerimento della settimana

La parte referente (“figlio”) dei campi che sono chiavi esterne dovrebbe in genere avere un indice, a meno che il valore referenziato abbia una cardinalità molto bassa. PostgreSQL non lo fa automaticamente.

Offerte di lavoro su PostgreSQL per maggio 2009

http://archives.postgresql.org/pgsql-jobs/2009-05/threads.php

Notizie locali su PostgreSQL

Il 20 maggio 2009 a Pisa, Gabriele Bartolini di 2ndQuadrant Italia parteciperà all’evento “Open-Source: aziende e studenti si incontrano”, organizzato dal TOSS-LAB (Tuscany Open Source Software Laboratory). Ulteriori informazioni: http://www.tosslab.it/open-source-aziende-e-studenti-si-incontrano

Nei giorni 21 e 22 maggio 2009 all’università di Ottawa, in Canada, si terrà PGCon 2009. Nei due giorni precedenti si terranno dei tutorials. http://www.pgcon.org/2009/

Il PgDay di Florianopolis (Brasile) sarà il 22 maggio. Mettetevi in contatto con Dickson S. Guedes (guedes AT guedesoft DOT net) per partecipare o inviare un lavoro. http://www.postgresql.org.br/eventos/pgday/sc

Segnatevi la data: pgDay San Jose (USA). Domenica 19 luglio subito prima di OSCON. Saranno presto annunciate ulteriori informazioni! (incluso il call for papers)

Il 23 e 24 ottobre 2009 si svolgerà PGCon Brazil, presso Unicamp, nella città di Campinas, stato di San Paolo.

Rassegna stampa su PostgreSQL

Planet PostgreSQL: http://planet.postgresql.org/

Questo notiziario settimanale PostgreSQL è stato realizzato da David Fetter e Josh Berkus; traduzione parziale in lingua italiana a cura di Gianni Ciolli.

Notizie o annunci destinati a questo notiziario dovranno pervenire entro la mezzanotte di domenica (le 15 nel fuso orario della California). I comunicati in lingua italiana dovranno essere inviati a pwn@itpug.org; per le lingue inglese o tedesca, si scriva rispettivamente a david@fetter.org o a pwd@pgug.de.

Patch applicate

Peter Eisentraut committed:

• Replace a couple of references to files that no longer exist in the source tree with references to the appropriate URLs. Robert Haas
• Disable the use of Unicode escapes in string constants (U&”) when standard_conforming_strings is not on, for security reasons.

Magnus Hagander committed:

• In pgsql/src/backend/port/win32_shmem.c, call SetLastError(0) before calling the file mapping functions to make sure that the error code is reset, as a precaution in case the API doesn’t properly reset it on success. This could be necessary, since we check the error value even if the function doesn’t fail for specific success cases.
• In pgsql/src/port/dirmod.c, update no longer current comments in header.
• In pgsql/src/backend/port/win32_shmem.c, make the win32 shared memory code try 10 times instead of one if it fails because the shared memory segment already exists. This means it can take up to 10 seconds before it reports the error if it does exist, but hopefully it will make the system capable of restarting even when the server is under high load.

Heikki Linnakangas committed:

• Fix the query used for d against 8.2 and 8.3 servers.
• Request XLOG switch before writing checkpoint in pg_start_backup(). Otherwise you can end up with an unrecoverable backup if you start a new base backup right after finishing archive recovery. In that scenario, the redo pointer of the checkpoint that pg_start_backup() writes points to the XLOG segment where the timeline-changing end-of-archive-recovery checkpoint is. The beginning of that segment contains pages with the old timeline ID, and we don’t accept that in recovery unless we find a history file covering the old timeline ID. If you omit pg_xlog from the base backup and clear the archive directory before starting the backup, there will be no such history file available. The bug is present in all versions since PITR was introduced in 8.0, but I’m back-patching only back to 8.2. Earlier versions didn’t have XLOG switch records, making this fix unfeasible. Given the lack of reports until now, it doesn’t seem worthwhile to spend more effort to fix 8.0 and 8.1. Per report and suggestion by Mikael Krantz
• Add alternative expected output files for cs_CZ locale for btree_gist and tsearch2 tests. This should make ‘comet_moth’ buildfarm member pass contrib check. Zdenek Kotala.

Tom Lane committed:

• In pgsql/src/bin/psql/describe.c, code review for df rewrite: fix assorted bugs, make type and volatility columns localizable.
• In pgsql/src/backend/commands/analyze.c, avoid integer overflow in the loop that extracts histogram entries from ANALYZE’s total sample. The original coding is at risk of overflow for statistics targets exceeding about 2675; this was not a problem before 8.4 but it is now. Per bug #4793 from Dennis Noordsij.
• In pgsql/src/backend/access/nbtree/nbtpage.c, update comment for _bt_relandgetbuf.
• Insert CHECK_FOR_INTERRUPTS() calls into btree and hash index scans at the points where we step right or left to the next page. This should ensure reasonable response time to a query cancel request during an unsuccessful index scan, as seen in recent gripe from Marc Cousin. It’s a bit trickier than it might seem at first glance, because CHECK_FOR_INTERRUPTS() is a no-op if executed while holding a buffer lock. So we have to do it just at the point where we’ve dropped one page lock and not yet acquired the next. Remove CHECK_FOR_INTERRUPTS calls at the top level of btgetbitmap and hashgetbitmap, since they’re pointless given the added checks. I think that GIST is okay already — at least, there’s a CHECK_FOR_INTERRUPTS at a plausible-looking place in gistnext(). I don’t claim to know GIN well enough to try to poke it for this, if indeed it has a problem at all. This is a pre-existing issue, but in view of the lack of prior complaints I’m not going to risk back-patching.
• Install a “dead man switch” to allow the postmaster to detect cases where a backend has done exit(0) or exit(1) without having disengaged itself from shared memory. We are at risk for this whenever third-party code is loaded into a backend, since such code might not know it’s supposed to go through proc_exit() instead. Also, it is reported that under Windows there are ways to externally kill a process that cause the status code returned to the postmaster to be indistinguishable from a voluntary exit (thank you, Microsoft). If this does happen then the system is probably hosed — for instance, the dead session might still be holding locks. So the best recovery method is to treat this like a backend crash. The dead man switch is armed for a particular child process when it acquires a regular PGPROC, and disarmed when the PGPROC is released; these should be the first and last touches of shared memory resources in a backend, or close enough anyway. This choice means there is no coverage for auxiliary processes, but I doubt we need that, since they shouldn’t be executing any user-provided code anyway. This patch also improves the management of the EXEC_BACKEND ShmemBackendArray array a bit, by reducing search costs. Although this problem is of long standing, the lack of field complaints seems to mean it’s not critical enough to risk back-patching; at least not till we get some more testing of this mechanism.
• In pgsql/src/backend/storage/ipc/ipc.c, install an atexit(2) callback that ensures that proc_exit’s cleanup processing will still be performed if something in a backend process calls exit() directly, instead of going through proc_exit() as we prefer. This is a second response to the issue that we might load third-party code that doesn’t know it should not call exit(). Such a call will now cause a reasonably graceful backend shutdown, if possible. (Of course, if the reason for the exit() call is out-of-memory or some such, we might not be able to recover, but at least we will try.)
• Make new complaint about unsafe Unicode literals include an error location. Every other ereport in scan.l has one, this should too.
• In pgsql/src/backend/port/win32_shmem.c, minor improvement: avoid assuming that GetLastError value cannot be affected by CloseHandle() or Sleep().
• In pgsql/src/backend/commands/dbcommands.c, tweak a comment to agree a bit better with the new dispensation that locales are database-wide, not server-wide.
• Fix ecpg tests for change that disallowed Unicode literals unless standard_conforming_strings is on.
• Modify CREATE DATABASE to enforce that the source database’s encoding setting must be used for the new database, except when copying from template0. This is the same rule that we now enforce for locale settings, and it has the same motivation: databases other than template0 might contain data that would be invalid according to a different setting. This represents another step in a continuing process of locking down ways in which encoding violations could occur inside the backend. Per discussion of a few days ago. In passing, fix pre-existing breakage of mbregress.sh, and fix up a couple of ereport() calls in dbcommands.c that failed to specify sqlstate codes.
• In pgsql/src/backend/optimizer/plan/initsplan.c, tweak distribute_qual_to_rels so that when we decide a pseudoconstant qual can be pushed to the top of the join tree, we update both the relids and qualscope variables to keep them in sync. This prevents a possible later failure of an Assert clause, and affects nothing else since qualscope isn’t used later except for that Assert. At the moment the Assert shouldn’t be reachable when we’ve pushed the qual up; but this is cheap insurance, and it’s more sensible anyway in terms of the overall logic of the routine. Per analysis of a bug report from Stefan Huehner. I’m not back-patching this since it’s just future-proofing; but if anyone gets tempted to change check_outerjoin_delay again in the back branches, this might be needed.
• In pgsql/src/backend/optimizer/plan/initsplan.c, ooops … make_outerjoininfo wasn’t actually enforcing the join order restrictions specified for semijoins in optimizer/README, to wit that you can’t reassociate outer joins into or out of the RHS of a semijoin. Per report from Heikki Linnakangas.
• Change pgbench to use the table names pgbench_accounts, pgbench_branches, pgbench_history, and pgbench_tellers, rather than just accounts, branches, history, and tellers. This is to prevent accidental conflicts with real application tables, as has been reported to happen at least once. Also remove the automatic “SET search_path = public” that it did at startup, as this seems to restrict testing flexibility without actually buying much. Per proposal by Joshua Drake and ensuing discussion. Joshua Drake and Tom Lane.
• Add an option to AlterTableCreateToastTable() to allow its caller to force a toast table to be built, even if the sum-of-column-widths calculation indicates one isn’t needed. This is needed by pg_migrator because if the old table has a toast table, we have to migrate over the toast table since it might contain some live data, even though subsequent column drops could mean that no recently-added rows could require toasting.

Bruce Momjian committed:

• In pgsql/src/include/access/transam.h, ‘PGDLLIMPORT’ ShmemVariableCache, needed for pg_migrator.so function linkage on Win32. Tested by Hiroshi Saito.
• In pgsql/src/tools/fsync/test_fsync.c, add missing third argument to open().

Patch rifiutate (per adesso)

No one was disappointed this week :-)

Patch in coda

Robert Haas sent in another revision of the ALTER TABLE … ALTER COLUMN … SET DISTINCT patch.

Andres Freund sent in two revisions of a patch which implements ALTER TABLE … DROP [COLUMN | CONSTRAINT] IF EXISTS …

Dickson S. Guedes sent in a patch to add a way to display both client and server versions in the psql prompt.

Seth Robertson sent in a patch to automate selection of client certificates in libpq.

Andrew (RhodiumToad) Gierth sent in a patch to change src/backend/libpq/be-secure.c from calling SSL_CTX_use_certificate_file to SSL_CTX_use_certificate_chain_file.

Joshua Drake sent in a patch to make version_stamp.pl strict-clean.

Khee Chin sent in a patch to make psql’s di show the type of index used.

David Fetter sent in a patch to make all the perl programs strict-clean.