PageGetFreeSpace() was being called while not holding the buffer lock, which
not only could yield a garbage answer, but even if it's the right answer there
might be less space available after we reacquire the buffer lock.
Also repair potential deadlock introduced by my recent performance improvement
in RelationGetBufferForTuple(): it was possible for two heap_updates to try to
lock two buffers in opposite orders. The fix creates a global rule that
buffers of a single heap relation should be locked in decreasing block number
order. Currently, this only applies to heap_update; VACUUM can get away with
ignoring the rule since it holds exclusive lock on the whole relation anyway.
However, if we try to implement a VACUUM that can run in parallel with other
transactions, VACUUM will also have to obey the lock order rule.
when we need to move to a new page; as long as we can insert the new
tuple on the same page as before, we only need LockBuffer and not the
expensive stuff. Also, twiddle bufmgr interfaces to avoid redundant
lseeks in RelationGetBufferForTuple and BufferAlloc. Successive inserts
now require one lseek per page added, rather than one per tuple with
several additional ones at each page boundary as happened before.
Lock contention when multiple backends are inserting in same table
is also greatly reduced.
a separate statement (though it can still be invoked as part of VACUUM, too).
pg_statistic redesigned to be more flexible about what statistics are
stored. ANALYZE now collects a list of several of the most common values,
not just one, plus a histogram (not just the min and max values). Random
sampling is used to make the process reasonably fast even on very large
tables. The number of values and histogram bins collected is now
user-settable via an ALTER TABLE command.
There is more still to do; the new stats are not being used everywhere
they could be in the planner. But the remaining changes for this project
should be localized, and the behavior is already better than before.
A not-very-related change is that sorting now makes use of btree comparison
routines if it can find one, rather than invoking '<' twice.
compressed storage works perfectly well. Might as well have a coherent
strategy for applying it, rather than the haphazard store-what-you-get
approach that was in the code before. The strategy I've set up here is
to attempt compression of any compressible index value exceeding
BLCKSZ/16, or about 500 bytes by default.
bothering to check the return value --- which meant that in case the
update or delete failed because of a concurrent update, you'd not find
out about it, except by observing later that the transaction produced
the wrong outcome. There are now subroutines simple_heap_update and
simple_heap_delete that should be used anyplace that you're not prepared
to do the full nine yards of coping with concurrent updates. In
practice, that seems to mean absolutely everywhere but the executor,
because *noplace* else was checking.
are now critical sections, so as to ensure die() won't interrupt us while
we are munging shared-memory data structures. Avoid insecure intermediate
states in some code that proc_exit will call, like palloc/pfree. Rename
START/END_CRIT_CODE to START/END_CRIT_SECTION, since that seems to be
what people tend to call them anyway, and make them be called with () like
a function call, in hopes of not confusing pg_indent.
I doubt that this is sufficient to make SIGTERM safe anywhere; there's
just too much code that could get invoked during proc_exit().
before calling RelationInvalidateHeapTuple(), which is bad because the
latter needs to look at the tuple data, which is in the shared disk
buffer. If another backend manages to recycle the buffer while this
is going on, we will compute the wrong hashindex for the tuple or
maybe even crash outright. Must hold buffer refcount until afterwards.
(This bug is not in 7.0.*; seems to be have introduced during WAL changes.)
1. Distinguish cases where a Datum representing a tuple datatype is an OID
from cases where it is a pointer to TupleTableSlot, and make sure we use
the right typlen in each case.
2. Make fetchatt() and related code support 8-byte by-value datatypes on
machines where Datum is 8 bytes. Centralize knowledge of the available
by-value datatype sizes in two macros in tupmacs.h, so that this will be
easier if we ever have to do it again.
both MULTIBYTE and TOAST prevent char(n) from being truly fixed-size.
Simplify and speed up fastgetattr() and index_getattr() macros by
eliminating special cases for attnum=1. It's just as fast to handle
the first attribute by presetting its attcacheoff to zero; so do that
instead when loading the tupledesc in relcache.c.
Context diff this time.
Remove -m486 compile args for FreeBSD-i386, compile -O2 on i386.
Compile with only -O on alpha for codegen safety.
Make the port use the TEST_AND_SET for alpha and i386 on FreeBSD.
Fix a lot of bogus string formats for outputting pointers (cast to int
and %u/%x replaced with no cast and %p), and 'Size'(size_t) are now
cast to 'unsigned long' and output with %lu/
Remove an unused variable.
Alfred Perlstein
(WAL logging for this is not done yet, however.) Clean up a number of really
crufty things that are no longer needed now that DROP behaves nicely. Make
temp table mapper do the right things when drop or rename affecting a temp
table is rolled back. Also, remove "relation modified while in use" error
check, in favor of locking tables at first reference and holding that lock
throughout the statement.
source, due to addition of header overhead), store it as plain data
rather than pseudo-compressed data. This saves a few microseconds when
reading it out, but much more importantly guarantees that the toaster
won't actually expand tuples that contain incompressible data. That's
essential to avoid 'Tuple too big' failures with large objects.
trying to toast tuples inserted into toast tables! Fix is two-pronged:
first, ensure all columns of a toast table are marked attstorage='p',
and second, alter the target chunk size so that it's less than the
threshold for trying to toast a tuple. (Code tried to do that but the
expression was wrong.) A few cosmetic cleanups in tuptoaster too.
NOTE: initdb forced due to change in toaster chunk-size.
These two routines will now ALWAYS elog() on failure, whether you ask for
a lock or not. If you really want to get a NULL return on failure, call
the new routines heap_open_nofail()/heap_openr_nofail(). By my count there
are only about three places that actually want that behavior. There were
rather more than three places that were missing the check they needed to
make under the old convention :-(.
