[
https://issues.apache.org/jira/browse/RATIS-1979?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17827620#comment-17827620
]
Duong commented on RATIS-1979:
------------------------------
This includes to changes:
* For stateMachineCaching, the log entry (with stateMachine data trimmed) is
copied and independent from the original buffer. The zero-copy buffer can be
released independently from the LogSegment cache.
* However, the stateMachine data (which backed by the zero copy buffer) can be
cached by StateMachine. StateMachine will hold the reference count to the
stateMachine data entry if it caches the data. _StateMachine.read_ now provides
the data via a _ReferenceCountedObject._
> Correct LogEntryProto cache logic stateMachineCache
> ---------------------------------------------------
>
> Key: RATIS-1979
> URL: https://issues.apache.org/jira/browse/RATIS-1979
> Project: Ratis
> Issue Type: Sub-task
> Reporter: Duong
> Priority: Major
>
> With zero-copy (https://github.com/apache/ratis/pull/990), we rely on RaftLog
> cache eviction to release the zero-copy input streams.
> There's a problems, with stateMachineCachingEnabled, the cache-size of
> LogEntryproto is calculated with StateMachineData trimmed. That leave the
> actual cached size if a log entry is too small comparing to the amount of
> direct memory backed for the StateMachineData.
>
> {code:java}
> static long getEntrySize(LogEntryProto entry, Op op) {
> LogEntryProto e = entry;
> if (op == Op.CHECK_SEGMENT_FILE_FULL) {
> e = LogProtoUtils.removeStateMachineData(entry);
> } else if (op == Op.LOAD_SEGMENT_FILE || op ==
> Op.WRITE_CACHE_WITH_STATE_MACHINE_CACHE) {
> Preconditions.assertTrue(entry ==
> LogProtoUtils.removeStateMachineData(entry),
> () -> "Unexpected LogEntryProto with StateMachine data: op=" + op +
> ", entry=" + entry);
> } else {
> Preconditions.assertTrue(op == Op.WRITE_CACHE_WITHOUT_STATE_MACHINE_CACHE
> || op == Op.REMOVE_CACHE,
> () -> "Unexpected op " + op + ", entry=" + entry);
> }
> final int serialized = e.getSerializedSize();
> return serialized + CodedOutputStream.computeUInt32SizeNoTag(serialized) +
> 4L;
> } {code}
>
> With the default 200MB limit for raft log cache, cache eviction is likely
> never happens until the server run out of direct memory for zero-copy.
>
> Maybe for cache calculation, we should take the StateMachineData size into
> account.
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
