This recent maitenance update is released to address critical bug issues listed below:
1. Default block size increase for miners.Increase the default -maxblocksize to 350,000 bytes. Increase the default space for high-priority transactions to 30,000 bytes. Accomodate higher transaction volume, and to measure what percentage of hashing power simply goes along with defaults.
2. Remove the all-outputs-must-be-greater-than-CENT-to-qualify-as-free rule to simplify the transaction creation / handling logic
3. Lower maximum size for free transaction creation. Always pay a fee for transactions larger than 1,000 bytes to create space for more free transactions.
4. OSX block chain database corruption fixes
– Update leveldb to 1.13
– Use fcntl with `F_FULLSYNC` instead of fsync on OSX
– Use native Darwin memory barriers
– Replace use of mmap in leveldb for improved reliability (only on OSX)
5. Fix nodes forwarding transactions with empty vins and getting banned
6. Network code performance and robustness improvements
7. Additional debug.log logging for diagnosis of network problems, log timestamps by default
8. Fix Bitcoin-Qt startup crash when clicking dock icon on OSX
9. Fix memory leaks in CKey::SetCompactSignature() and Key::SignCompact()
10. Fix rare GUI crash on send
11. Various small GUI, documentation and build fixes
How to Upgrade
If you are running an older version, shut it down. Wait until it has completely shut down (which might take a few minutes for older versions), then run the installer (on Windows) or just copy over /Applications/Bitcoin-Qt (on Mac) or bitcoind/bitcoin-qt (on Linux). If you are upgrading from version 0.7.2 or earlier, the first time you run 0.8.6 your blockchain files will be re-indexed, which will take anywhere from 30 minutes to several hours, depending on the speed of your machine.
Word of advice
There have been frequent reports of users running out of virtual memory on 32-bit systems during the initial sync. Hence it is recommended to use a 64-bit executable if possible. A 64-bit executable for Windows is planned for 0.9.