Release Note Changes

Few proposals

- Can we say "smoothed" rather than "distributed" checkpoints?
"Smoothed checkpoints greatly reduce checkpoint I/O spikes"

- Heap-Only Tuples (HOT) accelerate space reuse for UPDATEs
change to
"Heap-Only Tuples (HOT) improve performance of frequent UPDATEs"

I also notice that two performance features have disappeared from the
release notes. (Presumably they have been removed from source). Both of
them have changes that can be seen by users, so can't see why we would
want them removed.

- Merge Join performance has been substantially improved by ring buffer
which avoids materializing the previous sort step. (Simon, Greg)

More info, not for release notes:
The materialization of the prior sort step would generally double the
time taken for the sort, so avoiding this effectively gives a 50%
performance gain on sorts that are part of large merge joins.

- WAL file switches don't update controlfile any longer. Recovery now
refers to the last checkpoint time, which may be many minutes earlier
than time previously mentioned. (Simon, Tom)

More info, not for release notes:
WAL file switches were performed holding important LWLocks, so this
improves scalability on high end systems as well as reducing response
time spikes under heavy load on all kinds of hardware.

--
Simon Riggs
2ndQuadrant http://www.2ndQuadrant.com