For locking purposes, we now regard heavyweight locks as mutually
non-conflicting between cooperating parallel processes.  There are some
possible pitfalls to this approach that are not to be taken lightly,
but it works OK for now and can be changed later if we find a better
approach.  Without this, it's very easy for parallel queries to
silently self-deadlock if the user backend holds strong relation locks.

Robert Haas, with help from Amit Kapila.  Thanks to Noah Misch and
Andres Freund for extensive discussion of possible issues with this
approach.

Backpatch certain files through 9.1

We do this mostly everywhere, so it seems just as well to do it here,
too.

Thomas Munro

Backpatch certain files through 9.0

This includes removing tabs after periods in C comments, which was
applied to back branches, so this change should not effect backpatching.

Update all files in head, and files COPYRIGHT and legal.sgml in all back
branches.

Fully update git head, and update back branches in ./COPYRIGHT and
legal.sgml files.

In the original coding of the autovacuum cancel feature, commit
acac68b2, an autovacuum process was
considered a target for cancellation if it was found to hard-block any
process examined in the deadlock search.  This patch tightens the test so
that the autovacuum must directly hard-block the current process.  This
should make the behavior more predictable in general, and in particular
it ensures that an autovacuum will not be canceled with less than
deadlock_timeout grace period.  In the old coding, it was possible for an
autovacuum to be canceled almost instantly, given unfortunate timing of two
or more other processes' lock attempts.

This also justifies the logging methodology in the recent commit
d7318d43; without this restriction, that
patch isn't providing enough information to see the connection of the
canceling process to the autovacuum.  Like that one, patch all the way
back.

Adds a counter that tracks number of deadlocks that occurred in
each database to pg_stat_database.

Magnus Hagander, reviewed by Jaime Casanova

This speeds up snapshot-taking and reduces ProcArrayLock contention.
Also, the PGPROC (and PGXACT) structures used by two-phase commit are
now allocated as part of the main array, rather than in a separate
array, and we keep ProcArray sorted in pointer order.  These changes
are intended to minimize the number of cache lines that must be pulled
in to take a snapshot, and testing shows a substantial increase in
performance on both read and write workloads at high concurrencies.

Pavan Deolasee, Heikki Linnakangas, Robert Haas

There may be some other places where we should use errdetail_internal,
but they'll have to be evaluated case-by-case.  This commit just hits
a bunch of places where invoking gettext is obviously a waste of cycles.

We had previously (af26857a)
established the U.S. spellings as standard.

provided by Andrew.

allowed different processes to have different addresses for the shmem segment
in quite a long time, but there were still a few places left that used the
old coding convention.  Clean them up to reduce confusion and improve the
compiler's ability to detect pointer type mismatches.

Kris Jurka

Robert Lor

query texts only to the server log.  This eliminates the issue of possible
leaking of security-sensitive data in other sessions' queries.  Since the
log is presumed secure, we can now log the queries of all sessions involved
in the deadlock, whether or not they belong to the same user as the one
reporting the failure.

(if they'd be visible to the current user in pg_stat_activity).

This might look like it's subject to race conditions, but it's actually
pretty safe because at the time DeadLockReport() is constructing the
report, we haven't yet aborted our transaction and so we can expect that
everyone else involved in the deadlock is still blocked on some lock.
(There are corner cases where that might not be true, such as a statement
timeout triggering in another backend before we finish reporting; but at
worst we'd report a misleading activity string, so it seems acceptable
considering the usefulness of reporting the queries.)

Original patch by Itagaki Takahiro, heavily modified by me.

to be locking another process (except when it's working to prevent Xid
wraparound problems).

within a signal handler (this might be safe given the relatively narrow code
range in which the interrupt is enabled, but it seems awfully risky); do issue
more informative log messages that tell what is being waited for and the exact
length of the wait; minor other code cleanup.  Greg Stark and Tom Lane

fixup various places in the tree that were clearing a StringInfo by hand.
Making this function a part of the API simplifies client code slightly,
and avoids needlessly peeking inside the StringInfo interface.

Simon Riggs

back-stamped for this.

backward compatibility for anyone using the old userlock code that's now
on pgfoundry --- locks from that code still show as 'userlock'.

contrib functionality.  Along the way, remove the USER_LOCKS configuration
symbol, since it no longer makes any sense to try to compile that out.
No user documentation yet ... mmoncure has promised to write some.
Thanks to Abhijit Menon-Sen for creating a first draft to work from.

hash tables, instead of the previous kluge involving multiple hash tables.
This partially undoes my patch of last December.

reduce contention for the former single LockMgrLock.  Per my recent
proposal.  I set it up for 16 partitions, but on a pgbench test this
gives only a marginal further improvement over 4 partitions --- we need
to test more scenarios to choose the number of partitions.

the data defining the semantics of a lock method (ie, conflict resolution
table and ancillary data, which is all constant) and the hash tables
storing the current state.  The only thing we give up by this is the
ability to use separate hashtables for different lock methods, but there
is no need for that anyway.  Put some extra fields into the LockMethod
definition structs to clean up some other uglinesses, like hard-wired
tests for DEFAULT_LOCKMETHOD and USER_LOCKMETHOD.  This commit doesn't
do anything about the performance issues we were discussing, but it clears
away some of the underbrush that's in the way of fixing that.

Essentially, we shoehorn in a lockable-object-type field by taking
a byte away from the lockmethodid, which can surely fit in one byte
instead of two.  This allows less artificial definitions of all the
other fields of LOCKTAG; we can get rid of the special pg_xactlock
pseudo-relation, and also support locks on individual tuples and
general database objects (including shared objects).  None of those
possibilities are actually exploited just yet, however.

I removed pg_xactlock from pg_class, but did not force initdb for
that change.  At this point, relkind 's' (SPECIAL) is unused and
could be removed entirely.