Benedict created CASSANDRA-9834:
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Summary: Merge Hints/CommitLog/BatchLog
Key: CASSANDRA-9834
URL: https://issues.apache.org/jira/browse/CASSANDRA-9834
Project: Cassandra
Issue Type: Improvement
Components: Core
Reporter: Benedict
Fix For: 3.x
As discussed briefly on CASSANDRA-6230, it should be quite possible to
construct a single log that can serve as commit log, hints log and batch log.
The basic idea would be to write sequentially, marking messages as members of
one or more logical logs. We have a separate efficient (possibly embedded)
ledger for invalidation of log records. As entire log segments become
invalidated, we simply delete them; the rest we accumulate until we hit a high
watermark, and have segments that are at least half empty, at which point we
begin rewriting the emptiest.
This absolutely bounds our worst case sequential IO at 2x that used by _just_
the commit log, with normal operation under sufficiently high watermark having
zero overhead. The upper bound for space utilisation is the smaller of 2x the
actual amount of data stored, and our high watermark. This gives us batch and
hints for free, and eliminates OOMs from hints.
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