2. improve vacuum for gist
   - use FSM
   - full vacuum:
      - reforms parent tuple if it's needed
        ( tuples was deleted on child page or parent tuple remains invalid
          after crash recovery )
      - truncate index file if possible
3. fixes bugs and mistakes

'register' qualifier, make some function declarations more consistent,
and so on.

buildfarm machines.

investigate buildfarm failures.

scankeys arrays that it needs can never have more than INDEX_MAX_KEYS
entries, so it's reasonable to just allocate them as fixed-size local
arrays, and save the cost of palloc/pfree.  Not a huge savings, but
a cycle saved is a cycle earned ...

includes error checking and an appropriate ereport(ERROR) message.
This gets rid of rather tedious and error-prone manipulation of errno,
as well as a Windows-specific bug workaround, at more than a dozen
call sites.  After an idea in a recent patch by Heikki Linnakangas.

given reasonably short lifespans for prepared transactions, this should
mean that only a small minority of state files ever need to be fsynced
at all.  Per discussion with Heikki Linnakangas.

Andreas Pflug

Michael Fuhr

not memcpy() to copy the offered key into the hash table during HASH_ENTER.
This avoids possible core dump if the passed key is located very near the
end of memory.  Per report from Stefan Kaltenbrunner.

old suggestion by Oliver Jowett.  Also, add a transaction column to the
pg_locks view to show the xid of each transaction holding or awaiting
locks; this allows prepared transactions to be properly associated with
the locks they own.  There was already a column named 'transaction',
and I chose to rename it to 'transactionid' --- since this column is
new in the current devel cycle there should be no backwards compatibility
issue to worry about.

releasing locks, so COMMIT PREPARED should too.

< * -Add two-phase commit [2phase]
> * -Add two-phase commit

< * Add two-phase commit [2phase]
> * -Add two-phase commit [2phase]

hacking by Alvaro Herrera and Tom Lane.

> * Auto-fill the free space map by scanning the buffer cache or by
>   checking pages written by the background writer
< * Auto-fill the free space map by scanning the buffer cache or by
<   checking pages written by the background writer

* Auto-fill the free space map by scanning the buffer cache or by
  checking pages written by the background writer

Kris Jurka

>
> * Create a bitmap of pages that need vacuuming
>
>   Instead of sequentially scanning the entire table, have the background
>   writer or some other process record pages that have expired rows, then
>   VACUUM can look at just those pages rather than the entire table.  In
>   the event of a system crash, the bitmap would probably be invalidated.

where we need fsync().

shows that adding a circular shift between words greatly improves the
distribution of hash outputs.

 Cosimo Streppone

work if either of the join relations are empty. The logic is:

(1) if the inner relation's startup cost is less than the outer
    relation's startup cost and this is not an outer join, read
    a single tuple from the inner relation via ExecHash()
      - if NULL, we're done

(2) read a single tuple from the outer relation
      - if NULL, we're done

(3) build the hash table on the inner relation
      - if hash table is empty and this is not an outer join,
        we're done

(4) otherwise, do hash join as usual

The implementation uses the new MultiExecProcNode API, per a
suggestion from Tom: invoking ExecHash() now produces the first
tuple from the Hash node's child node, whereas MultiExecHash()
builds the hash table.

I had to put in a bit of a kludge to get the row count returned
for EXPLAIN ANALYZE to be correct: since ExecHash() is invoked to
return a tuple, and then MultiExecHash() is invoked, we would
return one too many tuples to EXPLAIN ANALYZE. I hacked around
this by just manually detecting this situation and subtracting 1
from the EXPLAIN ANALYZE row count.

prevents a large number of *.backup files from existing in pg_xlog/