This clause changes the behavior of SELECT locking clauses in the
presence of locked rows: instead of causing a process to block waiting
for the locks held by other processes (or raise an error, with NOWAIT),
SKIP LOCKED makes the new reader skip over such rows. While this is not
appropriate behavior for general purposes, there are some cases in which
it is useful, such as queue-like tables.
Catalog version bumped because this patch changes the representation of
stored rules.
Reviewed by Craig Ringer (based on a previous attempt at an
implementation by Simon Riggs, who also provided input on the syntax
used in the current patch), David Rowley, and Álvaro Herrera.
Author: Thomas Munro
The default for the choice attribute of the <arg> element is "opt",
which would normally put the argument inside brackets. But the DSSSL
stylesheets contain a hack that treats <arg> directly inside <group>
specially, so that <group><arg>-x</arg><arg>-y</arg></group> comes out
as [ -x | -y ] rather than [ [-x] | [-y] ], which it would technically
be. But when building man pages, this doesn't work, and so the
command synopses on the man pages contain lots of extra brackets.
By putting choice="opt" or choice="plain" explicitly on every <arg>
and <group> element, we avoid any toolchain dependencies like that,
and it also makes it clearer in the source code what is meant.
In passing, make some small corrections in the documentation about
which arguments are really optional or not.
Block elements with verbatim formatting (literallayout, programlisting,
screen, synopsis) should be aligned at column 0 independent of the surrounding
SGML, because whitespace is significant, and indenting them creates erratic
whitespace in the output. The CSS stylesheets already take care of indenting
the output.
Assorted markup improvements to go along with it.
(or RETURNING), but only when the output name is not any SQL keyword.
This seems as close as we can get to the standard's syntax without a
great deal of thrashing. Original patch by Hiroshi Saito, amended by me.
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
Also update two error messages mentioned in the documenation to match.
per-column options for btree indexes. The planner's support for this is still
pretty rudimentary; it does not yet know how to plan mergejoins with
nondefault ordering options. The documentation is pretty rudimentary, too.
I'll work on improving that stuff later.
Note incompatible change from prior behavior: ORDER BY ... USING will now be
rejected if the operator is not a less-than or greater-than member of some
btree opclass. This prevents less-than-sane behavior if an operator that
doesn't actually define a proper sort ordering is selected.
the opportunity to treat COUNT(*) as a zero-argument aggregate instead
of the old hack that equated it to COUNT(1); this is materially cleaner
(no more weird ANYOID cases) and ought to be at least a tiny bit faster.
Original patch by Sergey Koposov; review, documentation, simple regression
tests, pg_dump and psql support by moi.
support both FOR UPDATE and FOR SHARE in one command, as well as both
NOWAIT and normal WAIT behavior. The more general code is actually
simpler and cleaner.
to eliminate unnecessary deadlocks. This commit adds SELECT ... FOR SHARE
paralleling SELECT ... FOR UPDATE. The implementation uses a new SLRU
data structure (managed much like pg_subtrans) to represent multiple-
transaction-ID sets. When more than one transaction is holding a shared
lock on a particular row, we create a MultiXactId representing that set
of transactions and store its ID in the row's XMAX. This scheme allows
an effectively unlimited number of row locks, just as we did before,
while not costing any extra overhead except when a shared lock actually
has to be shared. Still TODO: use the regular lock manager to control
the grant order when multiple backends are waiting for a row lock.
Alvaro Herrera and Tom Lane.
(materialization into a tuple store) discussed on pgsql-hackers earlier.
I've updated the documentation and the regression tests.
Notes on the implementation:
- I needed to change the tuple store API slightly -- it assumes that it
won't be used to hold data across transaction boundaries, so the temp
files that it uses for on-disk storage are automatically reclaimed at
end-of-transaction. I added a flag to tuplestore_begin_heap() to control
this behavior. Is changing the tuple store API in this fashion OK?
- in order to store executor results in a tuple store, I added a new
CommandDest. This works well for the most part, with one exception: the
current DestFunction API doesn't provide enough information to allow the
Executor to store results into an arbitrary tuple store (where the
particular tuple store to use is chosen by the call site of
ExecutorRun). To workaround this, I've temporarily hacked up a solution
that works, but is not ideal: since the receiveTuple DestFunction is
passed the portal name, we can use that to lookup the Portal data
structure for the cursor and then use that to get at the tuple store the
Portal is using. This unnecessarily ties the Portal code with the
tupleReceiver code, but it works...
The proper fix for this is probably to change the DestFunction API --
Tom suggested passing the full QueryDesc to the receiveTuple function.
In that case, callers of ExecutorRun could "subclass" QueryDesc to add
any additional fields that their particular CommandDest needed to get
access to. This approach would work, but I'd like to think about it for
a little bit longer before deciding which route to go. In the mean time,
the code works fine, so I don't think a fix is urgent.
- (semi-related) I added a NO SCROLL keyword to DECLARE CURSOR, and
adjusted the behavior of SCROLL in accordance with the discussion on
-hackers.
- (unrelated) Cleaned up some SGML markup in sql.sgml, copy.sgml
Neil Conway
- more work from the SGML police
- some grammar improvements: rewriting a paragraph or two, replacing
contractions where (IMHO) appropriate
- fix missing utility commands in lock mode docs
- improve CLUSTER, REINDEX, SET SESSION AUTHORIZATION ref pages
Neil Conway
! DIFFERENCE (− or ∖): builds the set difference of
two tables. Let <classname>R</classname> and
<classname>S</classname>
again be two tables with the same
arity. <classname>R</classname> - <classname>S</classname>
--- 488,494 ----
<listitem>
<para>
! EXCEPT (− or ∖): builds the set difference of
(sql490.htm), there is
"set of all k-tuples v1, v2, ... vk, such that v1 [isin] D1, v1 [isin] D1"
i assume it should be
"set of all k-tuples v1, v2, ... vk, such that v1 [isin] D1, v2 [isin] D2"
Divide by Zero
ISO-compliant UNION/INTERSECT/EXCEPT. Revise discussion of rule
rewriter to reflect new subselect-in-FROM implementation of views.
Miscellaneous other cleanups.
> patches are not lost...
Aggregate doc patches:
The patches are attached. Be great if you could check them over to make
sure all relevant content (and markup) is there...
Isaac Wilcox
Add an appendix with more details on date/time attributes and handling.
Update most references to Postgres version numbers to 6.5,
*except* for the porting list which will require a report
from a successful installation to be updated.
Alvaro Herrera
Peter Eisentraut
Heikki Linnakangas
Magnus Hagander
Bruce Momjian
Tom Lane
Neil Conway
PostgreSQL Daemon
Thomas G. Lockhart