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2011-10-26Change FK trigger creation order to better support self-referential FKs.Tom Lane
When a foreign-key constraint references another column of the same table, row updates will queue both the PK's ON UPDATE action and the FK's CHECK action in the same event. The ON UPDATE action must execute first, else the CHECK will check a non-final state of the row and possibly throw an inappropriate error, as seen in bug #6268 from Roman Lytovchenko. Now, the firing order of multiple triggers for the same event is determined by the sort order of their pg_trigger.tgnames, and the auto-generated names we use for FK triggers are "RI_ConstraintTrigger_NNNN" where NNNN is the trigger OID. So most of the time the firing order is the same as creation order, and so rearranging the creation order fixes it. This patch will fail to fix the problem if the OID counter wraps around or adds a decimal digit (eg, from 99999 to 100000) while we are creating the triggers for an FK constraint. Given the small odds of that, and the low usage of self-referential FKs, we'll live with that solution in the back branches. A better fix is to change the auto-generated names for FK triggers, but it seems unwise to do that in stable branches because there may be client code that depends on the naming convention. We'll fix it that way in HEAD in a separate patch. Back-patch to all supported branches, since this bug has existed for a long time.
2011-09-06Avoid possibly accessing off the end of memory in examine_attribute().Tom Lane
Since the last couple of columns of pg_type are often NULL, sizeof(FormData_pg_type) can be an overestimate of the actual size of the tuple data part. Therefore memcpy'ing that much out of the catalog cache, as analyze.c was doing, poses a small risk of copying past the end of memory and incurring SIGSEGV. No such crash has been identified in the field, but we've certainly seen the equivalent happen in other code paths, so patch this one all the way back. Per valgrind testing by Noah Misch, though this is not his proposed patch. I chose to use SearchSysCacheCopy1 rather than inventing special-purpose infrastructure for copying only the minimal part of a pg_type tuple.
2011-08-30Fix a missed case in code for "moving average" estimate of reltuples.Tom Lane
It is possible for VACUUM to scan no pages at all, if the visibility map shows that all pages are all-visible. In this situation VACUUM has no new information to report about the relation's tuple density, so it wasn't changing pg_class.reltuples ... but it updated pg_class.relpages anyway. That's wrong in general, since there is no evidence to justify changing the density ratio reltuples/relpages, but it's particularly bad if the previous state was relpages=reltuples=0, which means "unknown tuple density". We just replaced "unknown" with "zero". ANALYZE would eventually recover from this, but it could take a lot of repetitions of ANALYZE to do so if the relation size is much larger than the maximum number of pages ANALYZE will scan, because of the moving-average behavior introduced by commit b4b6923e03f4d29636a94f6f4cc2f5cf6298b8c8. The only known situation where we could have relpages=reltuples=0 and yet the visibility map asserts everything's visible is immediately following a pg_upgrade. It might be advisable for pg_upgrade to try to preserve the relpages/reltuples statistics; but in any case this code is wrong on its own terms, so fix it. Per report from Sergey Koposov. Back-patch to 8.4, where the visibility map was introduced, same as the previous change.
2011-08-21Fix trigger WHEN conditions when both BEFORE and AFTER triggers exist.Tom Lane
Due to tuple-slot mismanagement, evaluation of WHEN conditions for AFTER ROW UPDATE triggers could crash if there had been a BEFORE ROW trigger fired for the same update. Fix by not trying to overload the use of estate->es_trig_tuple_slot. Per report from Yoran Heling. Back-patch to 9.0, when trigger WHEN conditions were introduced.
2011-08-16Preserve toast value OIDs in toast-swap-by-content for CLUSTER/VACUUM FULL.Tom Lane
This works around the problem that a catalog cache entry might contain a toast pointer that we try to dereference just as a VACUUM FULL completes on that catalog. We will see the sinval message on the cache entry when we acquire lock on the toast table, but by that point we've already told tuptoaster.c "here's the pointer to fetch", so it's difficult from a code structural standpoint to update the pointer before we use it. Much less painful to ensure that toast pointers are not invalidated in the first place. We have to add a bit of code to deal with the case that a value that previously wasn't toasted becomes so; but that should be a seldom-exercised corner case, so the inefficiency shouldn't be significant. Back-patch to 9.0. In prior versions, we didn't allow CLUSTER on system catalogs, and VACUUM FULL didn't result in reassignment of toast OIDs, so there was no problem.
2011-08-14Fix unsafe order of operations in foreign-table DDL commands.Tom Lane
When updating or deleting a system catalog tuple, it's necessary to acquire RowExclusiveLock on the catalog before looking up the tuple; otherwise a concurrent VACUUM FULL on the catalog might move the tuple to a different TID before we can apply the update. Coding patterns that find the tuple via a table scan aren't at risk here, but when obtaining the tuple from a catalog cache, correct ordering is important; and several routines in foreigncmds.c got it wrong. Noted while running the regression tests in parallel with VACUUM FULL of assorted system catalogs. For consistency I moved all the heap_open calls to the starts of their functions, including a couple for which there was no actual bug. Back-patch to 8.4 where foreigncmds.c was added.
2011-07-03Fix EXPLAIN to handle gating Result nodes within inner-indexscan subplans.Tom Lane
It is possible for a NestLoop plan node to pass an OUTER Var into an "inner indexscan" that is an Append construct (derived from an inheritance tree or UNION ALL subquery). The OUTER tuple is then passed down at runtime to the leaf indexscan node(s) where it will actually be used. EXPLAIN has to likewise pass the information about the nestloop's outer subplan down through the Append node, else it will fail to print the outer-reference Vars (with complaints like "bogus varno: 65001"). However, there was a case missed in all this: we could also have gating Result nodes that were inserted into the appendrel plan tree to deal with pseudoconstant qual conditions. So EXPLAIN has to pass down the outer plan node to a Result's subplan, too. Per example from Jon Nelson. The problem is gone in 9.1 because we replaced the nestloop outer-tuple kluge with a Param-based data transfer mechanism. Also, so far as I can tell, the case can't happen before 8.4 because of restrictions on what sorts of appendrel members could be pulled up into the parent query. So this patch is only needed for 8.4 and 9.0.
2011-06-19Fix thinko in previous patch to always update pg_class.reltuples/relpages.Tom Lane
I mis-simplified the test where ANALYZE decided if it could get away without doing anything: under the new regime, that's never allowed. Per bug #6068 from Jeff Janes. Back-patch to 8.4, just like previous patch.
2011-06-02Clean up after erroneous SELECT FOR UPDATE/SHARE on a sequence.Tom Lane
My previous commit disallowed this operation, but did nothing about cleaning up the damage if one had already been done. With the operation disallowed, it's okay to just forcibly clear xmax in a sequence's tuple, since any value seen there could not represent a live transaction's lock. So, any sequence-specific operation will repair the problem automatically, whether or not the user has already seen "could not access status of transaction" failures.
2011-05-30Fix VACUUM so that it always updates pg_class.reltuples/relpages.Tom Lane
When we added the ability for vacuum to skip heap pages by consulting the visibility map, we made it just not update the reltuples/relpages statistics if it skipped any pages. But this could leave us with extremely out-of-date stats for a table that contains any unchanging areas, especially for TOAST tables which never get processed by ANALYZE. In particular this could result in autovacuum making poor decisions about when to process the table, as in recent report from Florian Helmberger. And in general it's a bad idea to not update the stats at all. Instead, use the previous values of reltuples/relpages as an estimate of the tuple density in unvisited pages. This approach results in a "moving average" estimate of reltuples, which should converge to the correct value over multiple VACUUM and ANALYZE cycles even when individual measurements aren't very good. This new method for updating reltuples is used by both VACUUM and ANALYZE, with the result that we no longer need the grotty interconnections that caused ANALYZE to not update the stats depending on what had happened in the parent VACUUM command. Also, fix the logic for skipping all-visible pages during VACUUM so that it looks ahead rather than behind to decide what to do, as per a suggestion from Greg Stark. This eliminates useless scanning of all-visible pages at the start of the relation or just after a not-all-visible page. In particular, the first few pages of the relation will not be invariably included in the scanned pages, which seems to help in not overweighting them in the reltuples estimate. Back-patch to 8.4, where the visibility map was introduced.
2011-05-27Preserve caller's memory context in ProcessCompletedNotifies().Tom Lane
This is necessary to avoid long-term memory leakage, because the main loop in PostgresMain expects to be executing in MessageContext, and hence is a bit sloppy about freeing stuff that is only needed for the duration of processing the current client message. The known case of an actual leak is when encoding conversion has to be done on the incoming command string, but there might be others. Per report from Per-Olov Esgard. Back-patch to 9.0, where the bug was introduced by the LISTEN/NOTIFY rewrite.
2011-05-01Make CLUSTER lock the old table's toast table before copying data.Tom Lane
We must lock out autovacuuming of the old toast table before computing the OldestXmin horizon we will use. Otherwise, autovacuum could start on the toast table later, compute a later OldestXmin horizon, and remove as DEAD toast tuples that we still need (because we think their parent tuples are only RECENTLY_DEAD). Per further thought about bug #5998.
2011-04-19Avoid changing an index's indcheckxmin horizon during REINDEX.Tom Lane
There can never be a need to push the indcheckxmin horizon forward, since any HOT chains that are actually broken with respect to the index must pre-date its original creation. So we can just avoid changing pg_index altogether during a REINDEX operation. This offers a cleaner solution than my previous patch for the problem found a few days ago that we mustn't try to update pg_index while we are reindexing it. System catalog indexes will always be created with indcheckxmin = false during initdb, and with this modified code we should never try to change their pg_index entries. This avoids special-casing system catalogs as the former patch did, and should provide a performance benefit for many cases where REINDEX formerly caused an index to be considered unusable for a short time. Back-patch to 8.3 to cover all versions containing HOT. Note that this patch changes the API for index_build(), but I believe it is unlikely that any add-on code is calling that directly.
2011-03-28Prevent a rowtype from being included in itself.Tom Lane
Eventually we might be able to allow that, but it's not clear how many places need to be fixed to prevent infinite recursion when there's a direct or indirect inclusion of a rowtype in itself. One such place is CheckAttributeType(), which will recurse to stack overflow in cases such as those exhibited in bug #5950 from Alex Perepelica. If we were sure it was the only such place, we could easily modify the code added by this patch to stop the recursion without a complaint ... but it probably isn't the only such place. Hence, throw error until such time as someone is excited enough about this type of usage to put work into making it safe. Back-patch as far as 8.3. 8.2 doesn't have the recursive call in CheckAttributeType in the first place, so I see no need to add code there in the absence of clear evidence of a problem elsewhere.
2011-03-08Don't throw a warning if vacuum sees PD_ALL_VISIBLE flag set on a page thatHeikki Linnakangas
contains newly-inserted tuples that according to our OldestXmin are not yet visible to everyone. The value returned by GetOldestXmin() is conservative, and it can move backwards on repeated calls, so if we see that contradiction between the PD_ALL_VISIBLE flag and status of tuples on the page, we have to assume it's because an earlier vacuum calculated a higher OldestXmin value, and all the tuples really are visible to everyone. We have received several reports of this bug, with the "PD_ALL_VISIBLE flag was incorrectly set in relation ..." warning appearing in logs. We were finally able to hunt it down with David Gould's help to run extra diagnostics in an environment where this happened frequently. Also reword the warning, per Robert Haas' suggestion, to not imply that the PD_ALL_VISIBLE flag is necessarily at fault, as it might also be a symptom of corruption on a tuple header. Backpatch to 8.4, where the PD_ALL_VISIBLE flag was introduced.
2011-02-21Fix dangling-pointer problem in before-row update trigger processing.Tom Lane
ExecUpdate checked for whether ExecBRUpdateTriggers had returned a new tuple value by seeing if the returned tuple was pointer-equal to the old one. But the "old one" was in estate->es_junkFilter's result slot, which would be scribbled on if we had done an EvalPlanQual update in response to a concurrent update of the target tuple; therefore we were comparing a dangling pointer to a live one. Given the right set of circumstances we could get a false match, resulting in not forcing the tuple to be stored in the slot we thought it was stored in. In the case reported by Maxim Boguk in bug #5798, this led to "cannot extract system attribute from virtual tuple" failures when trying to do "RETURNING ctid". I believe there is a very-low-probability chance of more serious errors, such as generating incorrect index entries based on the original rather than the trigger-modified version of the row. In HEAD, change all of ExecBRInsertTriggers, ExecIRInsertTriggers, ExecBRUpdateTriggers, and ExecIRUpdateTriggers so that they continue to have similar APIs. In the back branches I just changed ExecBRUpdateTriggers, since there is no bug in the ExecBRInsertTriggers case.
2011-01-20Make ALTER TABLE revalidate uniqueness and exclusion constraints.Robert Haas
Failure to do so can lead to constraint violations. This was broken by commit 1ddc2703a936d03953657f43345460b9242bbed1 on 2010-02-07, so back-patch to 9.0. Noah Misch. Regression test by me.
2010-11-09Repair memory leakage while ANALYZE-ing complex index expressions.Tom Lane
The general design of memory management in Postgres is that intermediate results computed by an expression are not freed until the end of the tuple cycle. For expression indexes, ANALYZE has to re-evaluate each expression for each of its sample rows, and it wasn't bothering to free intermediate results until the end of processing of that index. This could lead to very substantial leakage if the intermediate results were large, as in a recent example from Jakub Ouhrabka. Fix by doing ResetExprContext for each sample row. This necessitates adding a datumCopy step to ensure that the final expression value isn't recycled too. Some quick testing suggests that this change adds at worst about 10% to the time needed to analyze a table with an expression index; which is annoying, but seems a tolerable price to pay to avoid unexpected out-of-memory problems. Back-patch to all supported branches.
2010-10-02Throw an appropriate error if ALTER COLUMN TYPE finds a dependent trigger.Tom Lane
Actually making this case work, if the column is used in the trigger's WHEN condition, will take some new code that probably isn't appropriate to back-patch. For now, just throw a FEATURE_NOT_SUPPORTED error rather than allowing control to reach the "unexpected object" case. Per bug #5688 from Daniel Grace. Back-patch to 9.0 where the possibility of such a dependency was introduced.
2010-09-23ProcessIncomingNotify *must* reset notifyInterruptOccurred when called.Tom Lane
This was broken in 9.0 by careless addition of an early-exit path. Bug report and diagnosis by Jeff Davis.
2010-09-23Prevent show_session_authorization from crashing when session_authorizationTom Lane
hasn't been set. The only known case where this can happen is when show_session_authorization is invoked in an autovacuum process, which is possible if an index function calls it, as for example in bug #5669 from Andrew Geery. We could perhaps try to return a sensible value, such as the name of the cluster-owning superuser; but that seems like much more trouble than the case is worth, and in any case it could create new possible failure modes. Simply returning an empty string seems like the most appropriate fix. Back-patch to all supported versions, even those before autovacuum, just in case there's another way to provoke this crash.
2010-09-22Fix remaining stray references to CVS.Tom Lane
These are just cosmetic and don't seem worth back-patching far. I put them into 9.0 just because it was trivial to do so.
2010-08-19Fix possible corruption of AfterTriggerEventLists in subtransaction rollback.Tom Lane
afterTriggerInvokeEvents failed to adjust events->tailfree when truncating the last chunk of an event list. This could result in the data being "de-truncated" by afterTriggerRestoreEventList during a subsequent subtransaction abort. Even that wouldn't kill us, because the re-added data would just be events marked DONE --- unless the data had been partially overwritten by new events. Then we might crash, or in any case misbehave (perhaps fire triggers twice, or fire triggers with the wrong event data). Per bug #5622 from Thue Janus Kristensen. Back-patch to 8.4 where the current trigger list representation was introduced.
2010-08-18Fix failure of "ALTER TABLE t ADD COLUMN c serial" when done by non-owner.Tom Lane
The implicitly created sequence was created as owned by the current user, who could be different from the table owner, eg if current user is a superuser or some member of the table's owning role. This caused sanity checks in the SEQUENCE OWNED BY code to spit up. Although possibly we don't need those sanity checks, the safest fix seems to be to make sure the implicit sequence is assigned the same owner role as the table has. (We still do all permissions checks as the current user, however.) Per report from Josh Berkus. Back-patch to 9.0. The bug goes back to the invention of SEQUENCE OWNED BY in 8.2, but the fix requires an API change for DefineRelation(), which seems to have potential for breaking third-party code if done in a minor release. Given the lack of prior complaints, it's probably not worth fixing in the stable branches.
2010-08-03Fix inheritance count tracking in ALTER TABLE .. ADD CONSTRAINT.Robert Haas
Without this patch, constraints inherited by children of a parent table which itself has multiple inheritance parents can end up with the wrong coninhcount. After dropping the constraint, the children end up with a leftover copy of the constraint that is not dumped and cannot be dropped. There is a similar problem with ALTER TABLE .. ADD COLUMN, but that looks significantly more difficult to resolve, so I'm committing this fix separately. Back-patch to 8.4, which is the first release that has coninhcount. Report by Hank Enting.
2010-08-01Fix ANALYZE's ancient deficiency of not trying to collect stats for expressionTom Lane
indexes when the index column type (the opclass opckeytype) is different from the expression's datatype. When coded, this limitation wasn't worth worrying about because we had no intelligence to speak of in stats collection for the datatypes used by such opclasses. However, now that there's non-toy estimation capability for tsvector queries, it amounts to a bug that ANALYZE fails to do this. The fix changes struct VacAttrStats, and therefore constitutes an API break for custom typanalyze functions. Therefore we can't back-patch it into released branches, but it was agreed that 9.0 isn't yet frozen hard enough to make such a change unacceptable. Ergo, back-patch to 9.0 but no further. The API break had better be mentioned in 9.0 release notes.
2010-07-29Fix another longstanding problem in copy_relation_data: it was blithelyTom Lane
assuming that a local char[] array would be aligned on at least a word boundary. There are architectures on which that is pretty much guaranteed to NOT be the case ... and those arches also don't like non-aligned memory accesses, meaning that log_newpage() would crash if it ever got invoked. Even on Intel-ish machines there's a potential for a large performance penalty from doing I/O to an inadequately aligned buffer. So palloc it instead. Backpatch to 8.0 --- 7.4 doesn't have this code.
2010-07-23Add more checks against altering typed tablesPeter Eisentraut
- Prohibit altering column type - Prohibit changing inheritance - Move checks from Exec to Prep phases in ALTER TABLE code backpatched to 9.0
2010-07-20Properly replay CREATE TABLESPACE during crash recovery by deletingBruce Momjian
directory/symlink before creation. Report from Tom Lane. Backpatch to 9.0.
2010-07-06pgindent run for 9.0, second runBruce Momjian
2010-07-03Allow REASSIGNED OWNED to handle opclasses and opfamilies.Robert Haas
Backpatch to 8.3, which is as far back as we have opfamilies. The opclass portion could probably be backpatched to 8.2, when REASSIGN OWNED was added, but for now I have not done that. Asko Tiidumaa, with minor adjustments by me.
2010-07-02Issue 'mkdir' hint when replying CREATE TABLESPACE in recovery mode.Bruce Momjian
Per idea from Fujii Masao
2010-07-01Allow ALTER TABLE .. SET TABLESPACE to be interrupted.Robert Haas
Backpatch to 8.0, where tablespaces were introduced. Guillaume Lelarge
2010-06-22Deprecate the use of => as an operator name.Robert Haas
In HEAD, emit a warning when an operator named => is defined. In both HEAD and the backbranches (except in 8.2, where contrib modules do not have documentation), document that hstore's text => text operator may be removed in a future release, and encourage the use of the hstore(text, text) function instead. This function only exists in HEAD (previously, it was called tconvert), so backpatch it back to 8.2, when hstore was added. Per discussion.
2010-06-13Fix ALTER LARGE OBJECT and GRANT ... ON LARGE OBJECT for large OIDs.Robert Haas
The previous coding failed for OIDs too large to be represented by a signed integer.
2010-06-10Quote all string values in EXPLAIN (FORMAT YAML) output.Robert Haas
While my previous attempt seems to always produce valid YAML, it doesn't always produce YAML that means what it appears to mean, because of tokens like "0xa" and "true", which without quotes will be interpreted as integer or Boolean literals. So, instead, just quote everything that's not known to be a number, as we do for JSON. Dean Rasheed, with some changes to the comments by me.
2010-06-09Attempt to fix EXPLAIN (FORMAT YAML) quoting to behave sanely.Robert Haas
The previous code failed to quote in many cases where quoting was necessary - YAML has loads of special characters, including -:[]{},"'|*& - so quote much more aggressively, and only refrain from quoting things where it seems fairly clear that it isn't necessary. Per report from Dean Rasheed.
2010-06-01Show schema name for REINDEX.Bruce Momjian
Greg Sabino Mullane
2010-05-27Make CREATE INDEX run expression preprocessing on a proposed index expressionTom Lane
before it checks whether the expression is immutable. This covers two cases that were previously handled poorly: 1. SQL function inlining could reduce the apparent volatility of the expression, allowing an expression to be accepted where it previously would not have been. As an example, polymorphic functions must be marked with the worst-case volatility they have for any argument type, but for specific argument types they might not be so volatile, so indexing could be allowed. (Since the planner will refuse to inline functions in cases where the apparent volatility of the expression would increase, this won't break any cases that were accepted before.) 2. A nominally immutable function could have default arguments that are volatile expressions. In such a case insertion of the defaults will increase both the apparent and actual volatility of the expression, so it is *necessary* to check this before allowing the expression to be indexed. Back-patch to 8.4, where default arguments were introduced.
2010-04-28Modify ShmemInitStruct and ShmemInitHash to throw errors internally,Tom Lane
rather than returning NULL for some-but-not-all failures as they used to. Remove now-redundant tests for NULL from call sites. We had to do something about this because many call sites were failing to check for NULL; and changing it like this seems a lot more useful and mistake-proof than adding checks to the call sites without them.
2010-04-28Introduce wal_level GUC to explicitly control if information needed forHeikki Linnakangas
archival or hot standby should be WAL-logged, instead of deducing that from other options like archive_mode. This replaces recovery_connections GUC in the primary, where it now has no effect, but it's still used in the standby to enable/disable hot standby. Remove the WAL-logging of "unlogged operations", like creating an index without WAL-logging and fsyncing it at the end. Instead, we keep a copy of the wal_mode setting and the settings that affect how much shared memory a hot standby server needs to track master transactions (max_connections, max_prepared_xacts, max_locks_per_xact) in pg_control. Whenever the settings change, at server restart, write a WAL record noting the new settings and update pg_control. This allows us to notice the change in those settings in the standby at the right moment, they used to be included in checkpoint records, but that meant that a changed value was not reflected in the standby until the first checkpoint after the change. Bump PG_CONTROL_VERSION and XLOG_PAGE_MAGIC. Whack XLOG_PAGE_MAGIC back to the sequence it used to follow, before hot standby and subsequent patches changed it to 0x9003.
2010-04-22Further reductions in Hot Standby conflict processing. TheseSimon Riggs
come from the realistion that HEAP2_CLEAN records don't always remove user visible data, so conflict processing for them can be skipped. Confirm validity using Assert checks, clarify circumstances under which we log heap_cleanup_info records. Tuning arises from bug fixing of earlier safety check failures.
2010-04-21Only send cleanup_info messages if VACUUM removes any tuples.Simon Riggs
There is no other purpose for this message type than to report the latestRemovedXid of removed tuples, prior to index scans. Removes overlooked path for sending invalid latestRemovedXid. Fixes buildfarm failure on centaur.
2010-04-21Fix oversight in collecting values for cleanup_info records.Simon Riggs
vacuum_log_cleanup_info() now generates log records with a valid latestRemovedXid set in all cases. Also be careful not to zero the value when we do a round of vacuuming part-way through lazy_scan_heap(). Incidentally, this reduces frequency of conflicts in Hot Standby.
2010-04-05Improve phrasing of warning message for NOTIFY queue getting too full.Tom Lane
Per gripe from Peter.
2010-03-22Shorten suffix of automatically created indexes to "_excl" when usingSimon Riggs
exclusion constraints, in line with string length of other pre-9.0 suffixes.
2010-03-20Forbid renaming columns of objects whose column names are system-generated.Robert Haas
KaiGai Kohei, with adjustments to the comments.
2010-03-10Fix incorrect comment about permissions checking being done in utility.c.Robert Haas
Noted while reviewing a patch from KaiGai Kohei.
2010-02-26pgindent run for 9.0Bruce Momjian
2010-02-23Add an OR REPLACE option to CREATE LANGUAGE.Tom Lane
This operates in the same way as other CREATE OR REPLACE commands, ie, it replaces everything but the ownership and ACL lists of an existing entry, and requires the caller to have owner privileges for that entry. While modifying an existing language has some use in development scenarios, in typical usage all the "replaced" values come from pg_pltemplate so there will be no actual change in the language definition. The reason for adding this is mainly to allow programs to ensure that a language exists without triggering an error if it already does exist. This commit just adds and documents the new option. A followon patch will use it to clean up some unpleasant cases in pg_dump and pg_regress.