Chunk server: fix buffer flush and limit calculation in writer append manager by just dividing equally the buffer allowance between all "active" appenders. Do not add appender to the pending flush list if less than full checksum block size is buffered, It is conceivable that excessive scans of pending flush list with large number of appenders made chunk server and append, in particular, cpu bound at much lower than expected throughput. Calculate and store next buffer alignment to avoid appender's mutex acquisition in GetAlignmentAndFwdFlag method. Remove appender's mutex acquisitions in the methods that do not access and/or change appender's state (io buffer and related variables) that can potentially change with client threads mutex held. Add appender's total pending byte, and low on buffers flush counters to the meta server heartbeat response.