Hello Dan Burkert, David Ribeiro Alves, Todd Lipcon,
I'd like you to do a code review. Please visit
http://gerrit.cloudera.org:8080/6946
to review the following change.
Change subject: consensus: consolidate Raft thread pools
......................................................................
consensus: consolidate Raft thread pools
This patch consolidates the two thread pools used in Raft consensus: the
observer and "Raft" (for lack of a better name) pools. The former runs tasks
for infrequent events such as term and config changes while the latter is
used for periodic events such as processing heartbeat responses.
In this patch, each per-replica pool is consolidated into a single
per-server pool. Sequence tokens are used to ensure that tasks belonging to
a single replica are executed serially and in order. For the "Raft" pool, a
single sequence token is shared by the PeerManager and RaftConsensus; this
mirrors the existing sharing behavior and is safe because token operations
are thread-safe.
The non-default max_threads may come as a surprise, but David showed me how
tasks submitted to either pool may sometimes lead to an fsync (mostly via
cmeta flushes). As such, it isn't safe to use the default num_cpus upper
bound, as that may cause such IO-based tasks to block other CPU-only tasks
(or worse, periodic tasks like heartbeat response processing).
What per-replica threads are not addressed by this patch?
- Failure detection thread: a threadpool isn't the right model
for these. Something like a hash wheel timer would be ideal.
- Prepare thread pool (max_threads=1): these could be consolidated too, but
their metrics are per-replica, and sequence tokens don't (yet) support
that. Meaning, if they were consolidated now, the metrics would also
consolidate and would be less useful as a result.
Change-Id: I8958c607d11ac2e94908670c985059bef0ff5f54
---
M src/kudu/consensus/consensus_peers-test.cc
M src/kudu/consensus/consensus_peers.cc
M src/kudu/consensus/consensus_peers.h
M src/kudu/consensus/consensus_queue-test.cc
M src/kudu/consensus/consensus_queue.cc
M src/kudu/consensus/consensus_queue.h
M src/kudu/consensus/peer_manager.cc
M src/kudu/consensus/peer_manager.h
M src/kudu/consensus/raft_consensus.cc
M src/kudu/consensus/raft_consensus.h
M src/kudu/consensus/raft_consensus_quorum-test.cc
M src/kudu/master/sys_catalog.cc
M src/kudu/server/server_base.cc
M src/kudu/server/server_base.h
M src/kudu/tablet/tablet_replica-test.cc
M src/kudu/tablet/tablet_replica.cc
M src/kudu/tablet/tablet_replica.h
M src/kudu/tserver/tablet_copy_source_session-test.cc
M src/kudu/tserver/ts_tablet_manager.cc
19 files changed, 188 insertions(+), 117 deletions(-)
git pull ssh://gerrit.cloudera.org:29418/kudu refs/changes/46/6946/1
--
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Gerrit-MessageType: newchange
Gerrit-Change-Id: I8958c607d11ac2e94908670c985059bef0ff5f54
Gerrit-PatchSet: 1
Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-Owner: Adar Dembo <[email protected]>
Gerrit-Reviewer: Dan Burkert <[email protected]>
Gerrit-Reviewer: David Ribeiro Alves <[email protected]>
Gerrit-Reviewer: Todd Lipcon <[email protected]>
