Bitcoin.org announced that the new is already ready for downloading. Users may also opt to upgrade the previous 0.10.0 version to access new features and implement bug fixes.
To upgrade, users simply need to shut down the older version then run the installer, which is compatible for both Windows and Mac. Downgrading to older versions are still possible but there might be compatibility issues with versions earlier than 0.10.0 because of the headers-first synchronization and parallel block download features.
Bitcoin Core Version Changes
In particular, downgrading to a pre-0.10.0 version of the software can result to blocks being stored on disk out of order and incompatibility with other tools or programs. Reindexing using earlier versions will also not work anymore as a result of this. Aside from that, the block index database will now hold headers for which no block is stored on disk, which earlier versions won’t support.
Some important information about the latest release also covers transaction flooding, block file pruning, big endian support, memory usage optimization, fee estimation changes, and privacy updates. To be specific, the bitcoin core version 0.11.0 release supports running a fully validating node without maintaining a copy of the raw block and undo data on disk.
A previous issue regarding the increased volume of transactions has severely affected the transaction verification time in the bitcoin network, and the new bitcoin core version attempts to address this. According to the blog post, if this growth of the mempool causes problematic memory use on the node, it is possible to change a few configuration options to work around this.
One is to increase the minimum transaction relay fee minrelaytxfee, which defaults to 0.00001. This will cause transactions with fewer BTC/kB fee to be rejected, and thus fewer transactions entering the mempool.
The other is to restrict the relaying of free transactions with limitfreerelay. This option sets the number of kB/minute at which free transactions (with enough priority) will be accepted. It defaults to 15. Reducing this number reduces the speed at which the mempool can grow due to free transactions.