an exclusive lock on the table at this point, which we want to release as soon
as possible. This is called in the phase of lazy vacuum where we truncate the
empty pages at the end of the table.
An alternative solution would be to lower the vacuum delay settings before
starting the truncating phase, but this doesn't work very well in autovacuum
due to the autobalancing code (which can cause other processes to change our
cost delay settings). This case could be considered in the balancing code, but
it is simpler this way.
Apparently it's a bug I introduced when I refactored spell.c to use the
readline function for reading and recoding the input file. I didn't
notice that some calls to STRNCMP used the non-lowercased version of the
input line.
and in passing, fix some bogosities dating from the custom_variable_classes
patch. Fix guc-file.l to correctly check changes in custom_variable_classes
that are attempted concurrently with additions/removals of custom variables,
and don't allow the new setting to be applied in advance of checking it.
Clean up messy and undocumented situation for string variables with NULL
boot_val. Fix DefineCustomVariable functions to initialize boot_val
correctly. Prevent find_option from inserting bogus placeholders for custom
variables that are simply inquired about rather than being set.
ReadNewTransactionId from GetSnapshotData --- with a "latestCompletedXid"
variable that is updated during transaction commit or abort. Since
latestCompletedXid is written only in places that had to lock ProcArrayLock
exclusively anyway, and is read only in places that had to lock ProcArrayLock
shared anyway, it adds no new locking requirements to the system despite being
cluster-wide. Moreover, removing ReadNewTransactionId from snapshot
acquisition eliminates the need to take both XidGenLock and ProcArrayLock at
the same time. Since XidGenLock is sometimes held across I/O this can be a
significant win. Some preliminary benchmarking suggested that this patch has
no effect on average throughput but can significantly improve the worst-case
transaction times seen in pgbench. Concept by Florian Pflug, implementation
by Tom Lane.
no need for serialization against snapshot-taking because the xact doesn't
affect anyone else's snapshot anyway. Per discussion. Also, move various
info about the interlocking of transactions and snapshots out of code comments
and into a hopefully-more-cohesive discussion in access/transam/README.
Also, remove a couple of now-obsolete comments about having to force some WAL
to be written to persuade RecordTransactionCommit to do its thing.
big misalignement, then it tries to split page basing on distribution
of boxe's centers.
Per report from Dolafi, Tom <dolafit@janelia.hhmi.org>
Backpatch is needed, change doesn't affect on-disk storage.
- change the alignment requirement of lexemes in TSVector slightly.
Lexeme strings were always padded to 2-byte aligned length to make sure
that if there's position array (uint16[]) it has the right alignment.
The patch changes that so that the padding is not done when there's no
positions. That makes the storage of tsvectors without positions
slightly more compact.
- added some #include "miscadmin.h" lines I missed in the earlier when I
added calls to check_stack_depth().
- Reimplement the send/recv functions, and added a comment
above them describing the on-wire format. The CRC is now recalculated in
tsquery as well per previous discussion.
- add code to check that the query tree is well-formed. It was indeed
possible to send malformed queries in binary mode, which produced all
kinds of strange results.
- make the left-field a uint32. There's no reason to
arbitrarily limit it to 16-bits, and it won't increase the disk/memory
footprint either now that QueryOperator and QueryOperand are separate
structs.
- add check_stack_depth() call to all recursive functions I found.
Some of them might have a natural limit so that you can't force
arbitrarily deep recursions, but check_stack_depth() is cheap enough
that seems best to just stick it into anything that might be a problem.
small editorization by me
- Brake the QueryItem struct into QueryOperator and QueryOperand.
Type was really the only common field between them. QueryItem still
exists, and is used in the TSQuery struct as before, but it's now a
union of the two. Many other changes fell from that, like separation
of pushval_asis function into pushValue, pushOperator and pushStop.
- Moved some structs that were for internal use only from header files
to the right .c-files.
- Moved tsvector parser to a new tsvector_parser.c file. Parser code was
about half of the size of tsvector.c, it's also used from tsquery.c, and
it has some data structures of its own, so it seems better to separate
it. Cleaned up the API so that TSVectorParserState is not accessed from
outside tsvector_parser.c.
- Separated enumerations (#defines, really) used for QueryItem.type
field and as return codes from gettoken_query. It was just accidental
code sharing.
- Removed ParseQueryNode struct used internally by makepol and friends.
push*-functions now construct QueryItems directly.
- Changed int4 variables to just ints for variables like "i" or "array
size", where the storage-size was not significant.
null::char(3) to a simple Const node. (It already worked for non-null values,
but not when we skipped evaluation of a strict coercion function.) This
prevents loss of typmod knowledge in situations such as exhibited in bug
#3598. Unfortunately there seems no good way to fix that bug in 8.1 and 8.2,
because they simply don't carry a typmod for a plain Const node.
In passing I made all the other callers of makeNullConst supply "real" typmod
values too, though I think it probably doesn't matter anywhere else.
that examine fields that could change under them. This is just to make
really sure that when we are fetching a value 'only once', that's what
actually happens. Possibly this is a bug that should be back-patched,
but in the absence of solid evidence that it's needed, I won't bother.
rows will normally never obtain an XID at all. We already did things this way
for subtransactions, but this patch extends the concept to top-level
transactions. In applications where there are lots of short read-only
transactions, this should improve performance noticeably; not so much from
removal of the actual XID-assignments, as from reduction of overhead that's
driven by the rate of XID consumption. We add a concept of a "virtual
transaction ID" so that active transactions can be uniquely identified even
if they don't have a regular XID. This is a much lighter-weight concept:
uniqueness of VXIDs is only guaranteed over the short term, and no on-disk
record is made about them.
Florian Pflug, with some editorialization by Tom.
(Actually, it works as a plain statement too, but I didn't document that
because it seems a bit useless.) Unify VariableResetStmt with
VariableSetStmt, and clean up some ancient cruft in the representation of
same.
initcap style --- the vast majority of the existing descriptions do not use
an initial cap. I didn't change places where the first word was all-cap.
initdb not forced because this doesn't change any regression test results.
operator-family rewrite. I had mistakenly supposed that these could use the
pg_amproc entries for text[] and inet[] respectively. However, binary
compatibility of the underlying types does not make two array types binary
compatible (since they must differ in the header field that gives the element
type OID), and so the index support code doesn't consider those entries
applicable. Add back the missing pg_amproc entries, and add an opr_sanity
query to try to catch such mistakes in future. Per report from Gregory
Maxwell.
There are still some loose ends: I didn't do anything about the SET FROM
CURRENT idea yet, and it's not real clear whether we are happy with the
interaction of SET LOCAL with function-local settings. The documentation
is a bit spartan, too.
regardless of the number of tuples involved, it's incorrect to skip it
when memtupcount = 1; the number of cycles saved is minuscule anyway.
An alternative solution would be to pull the state changes out to the
call site in tuplesort_performsort, but keeping them near the corresponding
changes in make_bounded_heap seems marginally cleaner. Noticed by
Greg Stark.
the number of rows likely to be produced by a query such as
SELECT * FROM t1 LEFT JOIN t2 USING (key) WHERE t2.key IS NULL;
What this is doing is selecting for t1 rows with no match in t2, and thus
it may produce a significant number of rows even if the t2.key table column
contains no nulls at all. 8.2 thinks the table column's null fraction is
relevant and thus may estimate no rows out, which results in terrible plans
if there are more joins above this one. A proper fix for this will involve
passing much more information about the context of a clause to the selectivity
estimator functions than we ever have. There's no time left to write such a
patch for 8.3, and it wouldn't be back-patchable into 8.2 anyway. Instead,
put in an ad-hoc test to defeat the normal table-stats-based estimation when
an IS NULL test is evaluated at an outer join, and just use a constant
estimate instead --- I went with 0.5 for lack of a better idea. This won't
catch every case but it will catch the typical ways of writing such queries,
and it seems unlikely to make things worse for other queries.
generating the tuples has resjunk output columns. This is not possible for
simple table scans but can happen when evaluating a whole-row Var for a view.
Per example from Patryk Kordylewski. The problem exists back to 8.0 but
I'm not going to risk back-patching further than 8.2 because of the many
changes in this area.
