blambov commented on code in PR #2777:
URL: https://github.com/apache/cassandra/pull/2777#discussion_r1354866011
##########
src/java/org/apache/cassandra/db/commitlog/CommitLogSegment.java:
##########
@@ -175,7 +177,10 @@ static long getNextId()
try
{
- channel = FileChannel.open(logFile.toPath(),
StandardOpenOption.WRITE, StandardOpenOption.READ, StandardOpenOption.CREATE);
+ if(commitLog.configuration.isDirectIOEnabled())
+ channel = FileChannel.open(logFile.toPath(),
StandardOpenOption.WRITE, StandardOpenOption.READ, StandardOpenOption.CREATE,
ExtendedOpenOption.DIRECT);
Review Comment:
Does this also change the compressed and encrypted segments to use
non-cached access? Could we also benchmark LZ4-compressed commit log with and
without the flag?
##########
conf/cassandra.yaml:
##########
@@ -2110,3 +2110,6 @@ drop_compact_storage_enabled: false
# a stable cluster. If a node from a previous version was started by
accident we won't any longer toggle behaviors as when UPGRADING.
#
storage_compatibility_mode: CASSANDRA_4
+
+# Enable Direct I/O feature for Commitlog files. Java-11 forces minimum
alignement to 4K and minimum disk write to 4K.
+direct_io_for_commitlog_enabled: true
Review Comment:
This setting should move with the other commit log settings, e.g.
[here](https://github.com/apache/cassandra/blob/624af90bab0d7f5f08de0b9d30cb212186c6bbdf/conf/cassandra.yaml#L582),
and the value needs to be an enum (with values `direct` and `mmap`), so that
users can understand what each option means.
See e.g. the implementation of `disk_access_mode`.
It also makes sense to unit test that the option is properly understood
(i.e. that the object created by `CommitLog.createSegment` is of the correct
type).
While I personally would prefer to switch to direct by default, please ask
on dev mailing list or at least in the JIRA ticket if anyone is opposed to that
as it might catch someone by surprise.
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