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Improvement

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This commit is contained in:
Alexey Milovidov 2020-06-12 23:32:31 +03:00
parent cfef7ba692
commit 6ff671b092
1 changed files with 16 additions and 1 deletions
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17
src/Storages/MergeTree/LeaderElection.h
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@ -29,8 +29,12 @@ namespace zkutil
* But then we decided to get rid of leader election, so every replica can become leader. * But then we decided to get rid of leader election, so every replica can become leader.
* For now, every replica can become leader if there is no leader among replicas with old version. * For now, every replica can become leader if there is no leader among replicas with old version.
* *
* It's tempting to remove this class at all, but we have to maintain it,
* to maintain compatibility when replicas with different versions work on the same cluster
* (this is allowed for short time period during cluster update).
*
* Replicas with old versions participate in leader election with ephemeral sequential nodes. * Replicas with old versions participate in leader election with ephemeral sequential nodes.
* If the node is first, then replica is leader. * If the node is first, then replica is the leader.
* Replicas with new versions creates persistent sequential nodes. * Replicas with new versions creates persistent sequential nodes.
* If the first node is persistent, then all replicas with new versions become leaders. * If the first node is persistent, then all replicas with new versions become leaders.
*/ */
@ -90,6 +94,17 @@ private:
void createNode() void createNode()
{ {
shutdown_called = false; shutdown_called = false;
/// If there is at least one persistent node, we don't have to create another.
Strings children = zookeeper.getChildren(path);
for (const auto & child : children)
{
Coordination::Stat stat;
zookeeper.get(path + "/" + child, &stat);
if (!stat.ephemeralOwner)
return;
}
zookeeper.create(path + "/leader_election-", identifier, CreateMode::PersistentSequential); zookeeper.create(path + "/leader_election-", identifier, CreateMode::PersistentSequential);
task->activateAndSchedule(); task->activateAndSchedule();
} }