OrientDB keeps locking records indefinitely

问题

I'm running OrientDB (community edition 2.2.9) in distributed mode with multiple nodes.

After a couple of minutes, I start getting the following error on my queries:

com.orientechnologies.orient.server.distributed.task.ODistributedRecordLockedException: Timeout (1500ms) on acquiring lock on record #1010:2651. It is locked by request 3.1000 DB name="MyDatabase"

The query in this instance looks like this:

UPDATE #1010:2651 SET name='foo';

The record remains locked and I can't run the query until I restart the database.

If I don't run the server in distributed mode, I don't get this error so it must have something to do with running it in distributed mode.

Here is my default-distributed-db-config.json

{
  "autoDeploy": true,
  "readQuorum": 1,
  "writeQuorum": 1,
  "executionMode": "asynchronous",
  "readYourWrites": true,
  "servers": {
    "*": "master"
  },
  "clusters": {
    "internal": {
    },
    "*": {
     "servers": ["<NEW_NODE>"]
    }
  }
}

I was using the following configuration in my orientdb-server-config.xml:

    ....
    <handler class="com.orientechnologies.orient.server.hazelcast.OHazelcastPlugin">
        <parameters>
            ....
            <parameter value="com.orientechnologies.orient.server.distributed.conflict.ODefaultReplicationConflictResolver" name="conflict.resolver.impl"/>
            ....
        </parameters>
    </handler>
   ...

By removing the "ODefaultReplicationConflictResolver" paramter from the config, the locking issue happens less frequently.

Why are the records locking up like this and how can I avoid it?

回答1:

Using asynchronous execution mode may cause this problem. See: Asynchronous replication mode.

You can try changing execution mode or try adding a retry into your query. Using Java: it is possible to catch events of command during asynchronous replication, thanks to the following method of OCommandSQL:

onAsyncReplicationOk(), to catch the event when the asynchronous replication succeed
onAsyncReplicationError(), to catch the event when the asynchronous replication returns error

Example retrying up to 3 times in case of concurrent modification exception on creation of edges:

g.command( new OCommandSQL("create edge Own from (select from User) to (select from Post)")
 .onAsyncReplicationError(new OAsyncReplicationError() {
  @Override
  public ACTION onAsyncReplicationError(Throwable iException, int iRetry) {
    System.err.println("Error, retrying...");
    return iException instanceof ONeedRetryException && iRetry<=3 ? ACTION.RETRY : ACTION.IGNORE;
  }
})
 .onAsyncReplicationOk(new OAsyncReplicationOk() {
   System.out.println("OK");
 }
).execute();

Or adding retry into a SQL Batch:

begin
let upd = UPDATE #1010:2651 SET name='foo'
commit retry 100
return $upd

Hope it helps.

来源：https://stackoverflow.com/questions/39494800/orientdb-keeps-locking-records-indefinitely

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OrientDB