Bitcoin 0.8.6 was officially released this week and the incremental update brings a few bug fixes and some nifty features, such as relaxed restrictions on block size.

The biggest changes affect block size. The maximum size of free transactions is now 1,000 bytes instead of 10,000 bytes, allowing more transactions per block. Since each block allows 27,000 bytes for free transactions, this means that as many as 27 free transactions will be available per block, up from three or less in 0.8.5 and previous releases.

The minimum output requirement of 0.01 BTC has been dropped, too. The requirement became outdated as bitcoin value surged. Smaller outputs can now qualify as for free relaying and the maximum size for free transaction creation has been reduced as well.

Bug fixes and tweaks

Bitcoin 0.8.6 also addresses a number of bugs found in 0.8.5, namely in users running Mac OSX. Block chain corruption issues in OSX have been resolved, alternative fsync methods have been introduced and a few other tweaks were implemented to improve reliability.

Many users of OSX 10.8 and 10.9 systems experienced problems with block chain corruption, but it is unclear whether 0.8.6 will resolve all issues.

Bitcoin 0.8.6 should resolve problems related to transaction broadcasting, as 0.8.5 was prone to mistakenly using the wrong vin value, resulting in an invalid transaction. The problem was patched and should be a thing of the past.

Network code performance and robustness were improved as well. There is a new timestamp debug log that can be used to detect and diagnose network problems.

Miner default block size increased

The default -maxblocksize was increased from 300,000 to 350,000 bytes. The default space for high-priority transactions has been bumped up to 30,000 bytes. This should accommodate higher transaction volume and help measure what percentage of hashing power simply goes along with defaults. However, most miners were not using the default limit anyway and block sizes were somewhat smaller than 300,000 bytes.

Possible update issues

There is a caveat. Some users have reported running out of virtual memory on 32-bit machines during the initial sync, so it is best to use a 64-bit executable, which is not available at this point. However, 0.9.0 should feature native 64-bit support.

The update urges all users to upgrade by following these steps:

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.

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