Commit Graph

1369 Commits

Author SHA1 Message Date
9a785aca87 Fix include-guard
Looks like a cut/paste error in the original addition of the file.

Andres Freund
2013-07-07 13:39:07 +02:00
a382997ee0 Fix to_char() to use ASCII-only case-folding rules where appropriate.
formatting.c used locale-dependent case folding rules in some code paths
where the result isn't supposed to be locale-dependent, for example
to_char(timestamp, 'DAY').  Since the source data is always just ASCII
in these cases, that usually didn't matter ... but it does matter in
Turkish locales, which have unusual treatment of "i" and "I".  To confuse
matters even more, the misbehavior was only visible in UTF8 encoding,
because in single-byte encodings we used pg_toupper/pg_tolower which
don't have locale-specific behavior for ASCII characters.  Fix by providing
intentionally ASCII-only case-folding functions and using these where
appropriate.  Per bug #7913 from Adnan Dursun.  Back-patch to all active
branches, since it's been like this for a long time.
2013-03-05 13:02:43 -05:00
dffc6c8a85 Back-patch fix for extraction of fixed prefixes from regular expressions.
Back-patch of commits 628cbb50ba80c83917b07a7609ddec12cda172d0 and
c6aae3042be5249e672b731ebeb21875b5343010.  This has been broken since
7.3, so back-patch to all supported branches.
2012-07-10 18:00:47 -04:00
5edd21de41 Refactor pattern_fixed_prefix() to avoid dealing in incomplete patterns.
Previously, pattern_fixed_prefix() was defined to return whatever fixed
prefix it could extract from the pattern, plus the "rest" of the pattern.
That definition was sensible for LIKE patterns, but not so much for
regexes, where reconstituting a valid pattern minus the prefix could be
quite tricky (certainly the existing code wasn't doing that correctly).
Since the only thing that callers ever did with the "rest" of the pattern
was to pass it to like_selectivity() or regex_selectivity(), let's cut out
the middle-man and just have pattern_fixed_prefix's subroutines do this
directly.  Then pattern_fixed_prefix can return a simple selectivity
number, and the question of how to cope with partial patterns is removed
from its API specification.

While at it, adjust the API spec so that callers who don't actually care
about the pattern's selectivity (which is a lot of them) can pass NULL for
the selectivity pointer to skip doing the work of computing a selectivity
estimate.

This patch is only an API refactoring that doesn't actually change any
processing, other than allowing a little bit of useless work to be skipped.
However, it's necessary infrastructure for my upcoming fix to regex prefix
extraction, because after that change there won't be any simple way to
identify the "rest" of the regex, not even to the low level of fidelity
needed by regex_selectivity.  We can cope with that if regex_fixed_prefix
and regex_selectivity communicate directly, but not if we have to work
within the old API.  Hence, back-patch to all active branches.
2012-07-09 23:23:16 -04:00
9b0875a204 Expand the allowed range of timezone offsets to +/-15:59:59 from Greenwich.
We used to only allow offsets less than +/-13 hours, then it was +/14,
then it was +/-15.  That's still not good enough though, as per today's bug
report from Patric Bechtel.  This time I actually looked through the Olson
timezone database to find the largest offsets used anywhere.  The winners
are Asia/Manila, at -15:56:00 until 1844, and America/Metlakatla, at
+15:13:42 until 1867.  So we'd better allow offsets less than +/-16 hours.

Given the history, we are way overdue to have some greppable #define
symbols controlling this, so make some ... and also remove an obsolete
comment that didn't get fixed the last time.

Back-patch to all supported branches.
2012-05-30 19:58:47 -04:00
e5f97c5f81 Fix CLUSTER/VACUUM FULL for toast values owned by recently-updated rows.
In commit 7b0d0e9356963d5c3e4d329a917f5fbb82a2ef05, I made CLUSTER and
VACUUM FULL try to preserve toast value OIDs from the original toast table
to the new one.  However, if we have to copy both live and recently-dead
versions of a row that has a toasted column, those versions may well
reference the same toast value with the same OID.  The patch then led to
duplicate-key failures as we tried to insert the toast value twice with the
same OID.  (The previous behavior was not very desirable either, since it
would have silently inserted the same value twice with different OIDs.
That wastes space, but what's worse is that the toast values inserted for
already-dead heap rows would not be reclaimed by subsequent ordinary
VACUUMs, since they go into the new toast table marked live not deleted.)

To fix, check if the copied OID already exists in the new toast table, and
if so, assume that it stores the desired value.  This is reasonably safe
since the only case where we will copy an OID from a previous toast pointer
is when toast_insert_or_update was given that toast pointer and so we just
pulled the data from the old table; if we got two different values that way
then we have big problems anyway.  We do have to assume that no other
backend is inserting items into the new toast table concurrently, but
that's surely safe for CLUSTER and VACUUM FULL.

Per bug #6393 from Maxim Boguk.  Back-patch to 9.0, same as the previous
patch.
2012-01-12 16:40:24 -05:00
6c0a375adf Revert the behavior of inet/cidr functions to not unpack the arguments.
I forgot to change the functions to use the PG_GETARG_INET_PP() macro,
when I changed DatumGetInetP() to unpack the datum, like Datum*P macros
usually do. Also, I screwed up the definition of the PG_GETARG_INET_PP()
macro, and didn't notice because it wasn't used.

This fixes the memory leak when sorting inet values, as reported
by Jochen Erwied and debugged by Andres Freund. Backpatch to 8.3, like
the previous patch that broke it.
2011-12-12 10:05:24 +02:00
a062ee4257 Make DatumGetInetP() unpack inet datums with a 1-byte header, and add
a new macro, DatumGetInetPP(), that does not. This brings these macros
in line with other DatumGet*P() macros.

Backpatch to 8.3, where 1-byte header varlenas were introduced.
2011-11-08 22:45:28 +02:00
93519b0c62 Fix race condition in relcache init file invalidation.
The previous code tried to synchronize by unlinking the init file twice,
but that doesn't actually work: it leaves a window wherein a third process
could read the already-stale init file but miss the SI messages that would
tell it the data is stale.  The result would be bizarre failures in catalog
accesses, typically "could not read block 0 in file ..." later during
startup.

Instead, hold RelCacheInitLock across both the unlink and the sending of
the SI messages.  This is more straightforward, and might even be a bit
faster since only one unlink call is needed.

This has been wrong since it was put in (in 2002!), so back-patch to all
supported releases.
2011-08-16 13:12:10 -04:00
9a9e530713 Fix another oversight in logging of changes in postgresql.conf settings.
We were using GetConfigOption to collect the old value of each setting,
overlooking the possibility that it didn't exist yet.  This does happen
in the case of adding a new entry within a custom variable class, as
exhibited in bug #6097 from Maxim Boguk.

To fix, add a missing_ok parameter to GetConfigOption, but only in 9.1
and HEAD --- it seems possible that some third-party code is using that
function, so changing its API in a minor release would cause problems.
In 9.0, create a near-duplicate function instead.
2011-07-08 17:03:12 -04:00
d6c1dc176a Create new errcode for recovery conflict caused by db drop on master.
Previously reported as ERRCODE_ADMIN_SHUTDOWN, this case is now
reported as ERRCODE_DATABASE_DROPPED. No message text change.
Unlikely to happen on most servers, so low impact change to allow
session poolers to correctly handle this situation.

Tatsuo Ishii and Simon Riggs
2011-02-01 08:49:58 +00:00
0fdf735d97 Avoid unexpected conversion overflow in planner for distant date values.
The "date" type supports a wider range of dates than int64 timestamps do.
However, there is pre-int64-timestamp code in the planner that assumes that
all date values can be converted to timestamp with impunity.  Fortunately,
what we really need out of the conversion is always a double (float8)
value; so even when the date is out of timestamp's range it's possible to
produce a sane answer.  All we need is a code path that doesn't try to
force the result into int64.  Per trouble report from David Rericha.

Back-patch to all supported versions.  Although this is surely a corner
case, there's not much point in advertising a date range wider than
timestamp's if we will choke on such values in unexpected places.
2010-12-28 22:50:19 -05:00
a692359411 Convert cvsignore to gitignore, and add .gitignore for build targets. 2010-09-22 12:57:06 +02:00
7c18d3f1e0 Fix up flushing of composite-type typcache entries to be driven directly by
SI invalidation events, rather than indirectly through the relcache.

In the previous coding, we had to flush a composite-type typcache entry
whenever we discarded the corresponding relcache entry.  This caused problems
at least when testing with RELCACHE_FORCE_RELEASE, as shown in recent report
from Jeff Davis, and might result in real-world problems given the kind of
unexpected relcache flush that that test mechanism is intended to model.

The new coding decouples relcache and typcache management, which is a good
thing anyway from a structural perspective.  The cost is that we have to
search the typcache linearly to find entries that need to be flushed.  There
are a couple of ways we could avoid that, but at the moment it's not clear
it's worth any extra trouble, because the typcache contains very few entries
in typical operation.

Back-patch to 8.2, the same as some other recent fixes in this general area.
The patch could be carried back to 8.0 with some additional work, but given
that it's only hypothetical whether we're fixing any problem observable in
the field, it doesn't seem worth the work now.
2010-09-02 03:16:52 +00:00
bdd538c571 Remove the single-argument form of string_agg(). It added nothing much in
functionality, while creating an ambiguity in usage with ORDER BY that at
least two people have already gotten seriously confused by.  Also, add an
opr_sanity test to check that we don't in future violate the newly minted
policy of not having built-in aggregates with the same name and different
numbers of parameters.  Per discussion of a complaint from Thom Brown.
2010-08-05 18:21:31 +00:00
538cb94db8 Rewrite the rbtree routines so that an RBNode is the first field of the
struct representing a tree entry, rather than being a separately allocated
piece of storage.  This API is at least as clean as the old one (if not
more so --- there were some bizarre choices in there) and it permits a
very substantial memory savings, on the order of 2X in ginbulk.c's usage.

Also, fix minor memory leaks in code called by ginEntryInsert, in
particular in ginInsertValue and entryFillRoot, as well as ginEntryInsert
itself.  These leaks resulted in the GIN index build context continuing
to bloat even after we'd filled it to maintenance_work_mem and started
to dump data out to the index.

In combination these fixes restore the GIN index build code to honoring
the maintenance_work_mem limit about as well as it did in 8.4.  Speed
seems on par with 8.4 too, maybe even a bit faster, for a non-pathological
case in which HEAD was formerly slower.

Back-patch to 9.0 so we don't have a performance regression from 8.4.
2010-08-01 02:12:51 +00:00
239d769e7e pgindent run for 9.0, second run 2010-07-06 19:19:02 +00:00
eb81b6509f The previous fix in CVS HEAD and 8.4 for handling the case where a cursor
being used in a PL/pgSQL FOR loop is closed was inadequate, as Tom Lane
pointed out. The bug affects FOR statement variants too, because you can
close an implicitly created cursor too by guessing the "<unnamed portal X>"
name created for it.

To fix that, "pin" the portal to prevent it from being dropped while it's
being used in a PL/pgSQL FOR loop. Backpatch all the way to 7.4 which is
the oldest supported version.
2010-07-05 09:27:18 +00:00
41f302b52a Add new GUC categories corresponding to sections in docs, and move
description for vacuum_defer_cleanup_age to the correct category.
Sections in postgresql.conf are also sorted in the same order with docs.

Per gripe by Fujii Masao, suggestion by Heikki Linnakangas, and patch by me.
2010-06-15 07:52:11 +00:00
26b7abfa32 Fix ALTER LARGE OBJECT and GRANT ... ON LARGE OBJECT for large OIDs.
The previous coding failed for OIDs too large to be represented by
a signed integer.
2010-06-13 17:43:13 +00:00
dd6fcd35e3 Change typedef for rb_appendator to avoid conflict with C++ reserved words.
Fixes a complaint from src/tools/pginclude/cpluspluscheck reported by
Peter Eisentraut.
2010-05-11 18:14:01 +00:00
90e04bab39 Patch revoked because of objections. 2010-04-24 16:20:32 +00:00
473af39737 Add missing optimizer hooks for function cost and number of rows.
Closely follow design of other optimizer hooks: if hook exists
retrieve value from plugin; if still not set then get from cache.
2010-04-23 22:23:39 +00:00
be8cebc717 Prevent ALTER USER f RESET ALL from removing the settings that were put there
by a superuser -- "ALTER USER f RESET setting" already disallows removing such a
setting.

Apply the same treatment to ALTER DATABASE d RESET ALL when run by a database
owner that's not superuser.
2010-03-25 14:44:34 +00:00
a6c1cea2b7 Add libpq warning message if the .pgpass-retrieved password fails.
Add ERRCODE_INVALID_PASSWORD sqlstate error code.
2010-03-13 14:55:57 +00:00
8bf14182cf Export xml.c's libxml-error-handling support so that contrib/xml2 can use it
too, instead of duplicating the functionality (badly).

I renamed xml_init to pg_xml_init, because the former seemed just a bit too
generic to be safe as a global symbol.  I considered likewise renaming
xml_ereport to pg_xml_ereport, but felt that the reference to ereport probably
made it sufficiently PG-centric already.
2010-03-03 17:29:45 +00:00
65e806cba1 pgindent run for 9.0 2010-02-26 02:01:40 +00:00
e26c539e9f Wrap calls to SearchSysCache and related functions using macros.
The purpose of this change is to eliminate the need for every caller
of SearchSysCache, SearchSysCacheCopy, SearchSysCacheExists,
GetSysCacheOid, and SearchSysCacheList to know the maximum number
of allowable keys for a syscache entry (currently 4).  This will
make it far easier to increase the maximum number of keys in a
future release should we choose to do so, and it makes the code
shorter, too.

Design and review by Tom Lane.
2010-02-14 18:42:19 +00:00
7507b193bc Don't expose the inline definition of MemoryContextSwitchTo when FRONTEND is
defined.  Its reference to CurrentMemoryContext causes link failures on some
platforms, evidently because the inline function gets compiled despite lack of
use.  Per buildfarm member warthog.
2010-02-13 20:46:52 +00:00
e08ab7c312 Support inlining various small performance-critical functions on non-GCC
compilers, by applying a configure check to see if the compiler will accept
an unreferenced "static inline foo ..." function without warnings.  It is
believed that such warnings are the only reason not to declare inlined
functions in headers, if the compiler understands "inline" at all.

Kurt Harriman
2010-02-13 02:34:16 +00:00
5209c084a6 Generic implementation of red-black binary tree. It's planned to use in
several places, but for now only GIN uses it during index creation.
Using self-balanced tree greatly speeds up index creation in corner cases
with preordered data.
2010-02-11 14:29:50 +00:00
cbe9d6beb4 Fix up rickety handling of relation-truncation interlocks.
Move rd_targblock, rd_fsm_nblocks, and rd_vm_nblocks from relcache to the smgr
relation entries, so that they will get reset to InvalidBlockNumber whenever
an smgr-level flush happens.  Because we now send smgr invalidation messages
immediately (not at end of transaction) when a relation truncation occurs,
this ensures that other backends will reset their values before they next
access the relation.  We no longer need the unreliable assumption that a
VACUUM that's doing a truncation will hold its AccessExclusive lock until
commit --- in fact, we can intentionally release that lock as soon as we've
completed the truncation.  This patch therefore reverts (most of) Alvaro's
patch of 2009-11-10, as well as my marginal hacking on it yesterday.  We can
also get rid of assorted no-longer-needed relcache flushes, which are far more
expensive than an smgr flush because they kill a lot more state.

In passing this patch fixes smgr_redo's failure to perform visibility-map
truncation, and cleans up some rather dubious assumptions in freespace.c and
visibilitymap.c about when rd_fsm_nblocks and rd_vm_nblocks can be out of
date.
2010-02-09 21:43:30 +00:00
9a75803b1a Remove CatalogCacheFlushRelation, and the reloidattr infrastructure that was
needed by nothing else.

The restructuring I just finished doing on cache management exposed to me how
silly this routine was.  Its function was to go into the catcache and blow
away all entries related to a given relation when there was a relcache flush
on that relation.  However, there is no point in removing a catcache entry
if the catalog row it represents is still valid --- and if it isn't valid,
there must have been a catcache entry flush on it, because that's triggered
directly by heap_update or heap_delete on the catalog row.  So this routine
accomplished nothing except to blow away valid cache entries that we'd very
likely be wanting in the near future to help reconstruct the relcache entry.
Dumb.

On top of which, it required a subtle and easy-to-get-wrong attribute in
syscache definitions, ie, the column containing the OID of the related
relation if any.  Removing that is a very useful maintenance simplification.
2010-02-08 05:53:55 +00:00
0a469c8769 Remove old-style VACUUM FULL (which was known for a little while as
VACUUM FULL INPLACE), along with a boatload of subsidiary code and complexity.
Per discussion, the use case for this method of vacuuming is no longer large
enough to justify maintaining it; not to mention that we don't wish to invest
the work that would be needed to make it play nicely with Hot Standby.

Aside from the code directly related to old-style VACUUM FULL, this commit
removes support for certain WAL record types that could only be generated
within VACUUM FULL, redirect-pointer removal in heap_page_prune, and
nontransactional generation of cache invalidation sinval messages (the last
being the sticking point for Hot Standby).

We still have to retain all code that copes with finding HEAP_MOVED_OFF and
HEAP_MOVED_IN flag bits on existing tuples.  This can't be removed as long
as we want to support in-place update from pre-9.0 databases.
2010-02-08 04:33:55 +00:00
b9b8831ad6 Create a "relation mapping" infrastructure to support changing the relfilenodes
of shared or nailed system catalogs.  This has two key benefits:

* The new CLUSTER-based VACUUM FULL can be applied safely to all catalogs.

* We no longer have to use an unsafe reindex-in-place approach for reindexing
  shared catalogs.

CLUSTER on nailed catalogs now works too, although I left it disabled on
shared catalogs because the resulting pg_index.indisclustered update would
only be visible in one database.

Since reindexing shared system catalogs is now fully transactional and
crash-safe, the former special cases in REINDEX behavior have been removed;
shared catalogs are treated the same as non-shared.

This commit does not do anything about the recently-discussed problem of
deadlocks between VACUUM FULL/CLUSTER on a system catalog and other
concurrent queries; will address that in a separate patch.  As a stopgap,
parallel_schedule has been tweaked to run vacuum.sql by itself, to avoid
such failures during the regression tests.
2010-02-07 20:48:13 +00:00
9727c583fe Restructure CLUSTER/newstyle VACUUM FULL/ALTER TABLE support so that swapping
of old and new toast tables can be done either at the logical level (by
swapping the heaps' reltoastrelid links) or at the physical level (by swapping
the relfilenodes of the toast tables and their indexes).  This is necessary
infrastructure for upcoming changes to support CLUSTER/VAC FULL on shared
system catalogs, where we cannot change reltoastrelid.  The physical swap
saves a few catalog updates too.

We unfortunately have to keep the logical-level swap logic because in some
cases we will be adding or deleting a toast table, so there's no possibility
of a physical swap.  However, that only happens as a consequence of schema
changes in the table, which we do not need to support for system catalogs,
so such cases aren't an obstacle for that.

In passing, refactor the cluster support functions a little bit to eliminate
unnecessarily-duplicated code; and fix the problem that while CLUSTER had
been taught to rename the final toast table at need, ALTER TABLE had not.
2010-02-04 00:09:14 +00:00
70a2b05a59 Assorted cleanups in preparation for using a map file to support altering
the relfilenode of currently-not-relocatable system catalogs.

1. Get rid of inval.c's dependency on relfilenode, by not having it emit
smgr invalidations as a result of relcache flushes.  Instead, smgr sinval
messages are sent directly from smgr.c when an actual relation delete or
truncate is done.  This makes considerably more structural sense and allows
elimination of a large number of useless smgr inval messages that were
formerly sent even in cases where nothing was changing at the
physical-relation level.  Note that this reintroduces the concept of
nontransactional inval messages, but that's okay --- because the messages
are sent by smgr.c, they will be sent in Hot Standby slaves, just from a
lower logical level than before.

2. Move setNewRelfilenode out of catalog/index.c, where it never logically
belonged, into relcache.c; which is a somewhat debatable choice as well but
better than before.  (I considered catalog/storage.c, but that seemed too
low level.)  Rename to RelationSetNewRelfilenode.

3. Cosmetic cleanups of some other relfilenode manipulations.
2010-02-03 01:14:17 +00:00
9ea9918e37 Add string_agg aggregate functions. The one argument version concatenates
the input values into a string. The two argument version also does the same
thing, but inserts delimiters between elements.

Original patch by Pavel Stehule, reviewed by David E. Wheeler and me.
2010-02-01 03:14:45 +00:00
d879697cd2 Remove the default_do_language parameter, instead making DO use a hardwired
default of "plpgsql".  This is more reasonable than it was when the DO patch
was written, because we have since decided that plpgsql should be installed
by default.  Per discussion, having a parameter for this doesn't seem useful
enough to justify the risk of application breakage if the value is changed
unexpectedly.
2010-01-26 16:33:40 +00:00
9507c8a1db Add get_bit/set_bit functions for bit strings, paralleling those for bytea,
and implement OVERLAY() for bit strings and bytea.

In passing also convert text OVERLAY() to a true built-in, instead of
relying on a SQL function.

Leonardo F, reviewed by Kevin Grittner
2010-01-25 20:55:32 +00:00
d779199175 Fix several oversights in previous commit - attribute options patch.
I failed to 'cvs add' the new files and also neglected to bump catversion.
2010-01-22 16:42:31 +00:00
4f15699d70 Add pg_table_size() and pg_indexes_size() to provide more user-friendly
wrappers around the pg_relation_size() function.

Bernd Helmle, reviewed by Greg Smith
2010-01-19 05:50:18 +00:00
9a915e596f Improve the handling of SET CONSTRAINTS commands by having them search
pg_constraint before searching pg_trigger.  This allows saner handling of
corner cases; in particular we now say "constraint is not deferrable"
rather than "constraint does not exist" when the command is applied to
a constraint that's inherently non-deferrable.  Per a gripe several months
ago from hubert depesz lubaczewski.

To make this work without breaking user-defined constraint triggers,
we have to add entries for them to pg_constraint.  However, in return
we can remove the pgconstrname column from pg_constraint, which represents
a fairly sizable space savings.  I also replaced the tgisconstraint column
with tgisinternal; the old meaning of tgisconstraint can now be had by
testing for nonzero tgconstraint, while there is no other way to get
the old meaning of nonzero tgconstraint, namely that the trigger was
internally generated rather than being user-created.

In passing, fix an old misstatement in the docs and comments, namely that
pg_trigger.tgdeferrable is exactly redundant with pg_constraint.condeferrable.
Actually, we mark RI action triggers as nondeferrable even when they belong to
a nominally deferrable FK constraint.  The SET CONSTRAINTS code now relies on
that instead of hard-coding a list of exception OIDs.
2010-01-17 22:56:23 +00:00
40f908bdcd Introduce Streaming Replication.
This includes two new kinds of postmaster processes, walsenders and
walreceiver. Walreceiver is responsible for connecting to the primary server
and streaming WAL to disk, while walsender runs in the primary server and
streams WAL from disk to the client.

Documentation still needs work, but the basics are there. We will probably
pull the replication section to a new chapter later on, as well as the
sections describing file-based replication. But let's do that as a separate
patch, so that it's easier to see what has been added/changed. This patch
also adds a new section to the chapter about FE/BE protocol, documenting the
protocol used by walsender/walreceivxer.

Bump catalog version because of two new functions,
pg_last_xlog_receive_location() and pg_last_xlog_replay_location(), for
monitoring the progress of replication.

Fujii Masao, with additional hacking by me
2010-01-15 09:19:10 +00:00
4cbe473938 Add point_ops opclass for GiST. 2010-01-14 16:31:09 +00:00
6164b4bc19 Some trivial adjustments in comments for struct RelationData. 2010-01-10 22:19:17 +00:00
50626efe0a Fix 3-parameter form of bit substring() to throw error for negative length,
as required by SQL standard.
2010-01-07 20:17:44 +00:00
901be0fad4 Remove all the special-case code for INT64_IS_BUSTED, per decision that
we're not going to support that anymore.

I did keep the 64-bit-CRC-with-32-bit-arithmetic code, since it has a
performance excuse to live.  It's a bit moot since that's all ifdef'd
out, of course.
2010-01-07 04:53:35 +00:00
d86d51a958 Support ALTER TABLESPACE name SET/RESET ( tablespace_options ).
This patch only supports seq_page_cost and random_page_cost as parameters,
but it provides the infrastructure to scalably support many more.
In particular, we may want to add support for effective_io_concurrency,
but I'm leaving that as future work for now.

Thanks to Tom Lane for design help and Alvaro Herrera for the review.
2010-01-05 21:54:00 +00:00
40608e7f94 When estimating the selectivity of an inequality "column > constant" or
"column < constant", and the comparison value is in the first or last
histogram bin or outside the histogram entirely, try to fetch the actual
column min or max value using an index scan (if there is an index on the
column).  If successful, replace the lower or upper histogram bound with
that value before carrying on with the estimate.  This limits the
estimation error caused by moving min/max values when the comparison
value is close to the min or max.  Per a complaint from Josh Berkus.

It is tempting to consider using this mechanism for mergejoinscansel as well,
but that would inject index fetches into main-line join estimation not just
endpoint cases.  I'm refraining from that until we can get a better handle
on the costs of doing this type of lookup.
2010-01-04 02:44:40 +00:00