Reduce schema pull request volume #582
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andybradshaw
commented
Nov 20, 2024
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Tested on a staging stack with a large number of nodes... we see the following log lines on a node that needs to catch up with some schema changes:
{"type":"service.1","level":"DEBUG","time":"2024-11-20T01:00:21.939519Z","origin":"org.apache.cassandra.service.MigrationManager","safe":true,"thread":"MigrationStage:1","message":"Gossiping my schema version {}","params":{},"uid":null,"sid":null,"tokenId":null,"traceId":"6d9ec00a8aad1bfe","stacktrace":null,"unsafeParams":{"0":"4211f487-13c9-3da0-8f09-77ff6dce868b"},"tags":{}}
{"type":"service.1","level":"DEBUG","time":"2024-11-20T01:00:22.547598Z","origin":"org.apache.cassandra.service.MigrationManager","safe":true,"thread":"GossipStage:1","message":"Evaluating schema pull criteria: other schema empty {}, no scheduled requests {}","params":{},"uid":null,"sid":null,"tokenId":null,"traceId":null,"stacktrace":null,"unsafeParams":{"0":true,"1":true},"tags":{}}
// ... many lines of the following ...
{"type":"service.1","level":"DEBUG","time":"2024-11-20T01:00:22.551392Z","origin":"org.apache.cassandra.service.MigrationManager","safe":true,"thread":"GossipStage:1","message":"Not pulling schema because versions match or shouldPullSchemaFrom returned false","params":{},"uid":null,"sid":null,"tokenId":null,"traceId":null,"stacktrace":null,"unsafeParams":{},"tags":{}}
{"type":"service.1","level":"DEBUG","time":"2024-11-20T01:00:22.553306Z","origin":"org.apache.cassandra.service.MigrationManager","safe":true,"thread":"GossipStage:1","message":"Evaluating schema pull criteria: other schema empty {}, no scheduled requests {}","params":{},"uid":null,"sid":null,"tokenId":null,"traceId":null,"stacktrace":null,"unsafeParams":{"0":true,"1":false},"tags":{}}
{"type":"service.1","level":"DEBUG","time":"2024-11-20T01:00:22.553320Z","origin":"org.apache.cassandra.service.MigrationManager","safe":true,"thread":"GossipStage:1","message":"Not pulling schema because versions match or shouldPullSchemaFrom returned false","params":{},"uid":null,"sid":null,"tokenId":null,"traceId":null,"stacktrace":null,"unsafeParams":{},"tags":{}}
{"type":"service.1","level":"DEBUG","time":"2024-11-20T01:00:22.555249Z","origin":"org.apache.cassandra.service.MigrationManager","safe":true,"thread":"GossipStage:1","message":"Evaluating schema pull criteria: other schema empty {}, no scheduled requests {}","params":{},"uid":null,"sid":null,"tokenId":null,"traceId":null,"stacktrace":null,"unsafeParams":{"0":true,"1":false},"tags":{}}
// ... finally actually submitting the migration task ...
{"type":"service.1","level":"DEBUG","time":"2024-11-20T01:01:41.249743Z","origin":"org.apache.cassandra.service.MigrationManager","safe":true,"thread":"NonPeriodicTasks:1","message":"submitting migration task for endpoint {}, endpoint schema version {}, and our schema version {}","params":{},"uid":null,"sid":null,"tokenId":null,"traceId":null,"stacktrace":null,"unsafeParams":{"0":"/10.100.169.237","1":"f4e89c16-e5a0-3cac-9aa8-93ea575fb472","2":"60a8b5bb-1e41-32ef-a40a-3112b19b6238"},"tags":{}}
| */ | ||
| boolean isOtherSchemaNonEmpty = !Schema.emptyVersion.equals(theirVersion); | ||
| boolean noScheduledRequests = !scheduledSchemaPulls.contains(theirVersion); | ||
| logger.debug("Evaluating schema pull criteria: other schema empty {}, no scheduled requests {}", isOtherSchemaNonEmpty, noScheduledRequests); |
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This was added for testing purposes... reminder to remove before merging. Also, got the log param message wrong 🤦♂️
| @@ -62,10 +62,13 @@ public class MigrationManager | |||
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| private static final RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean(); | |||
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| public static final Set<UUID> scheduledSchemaPulls = new ConcurrentSkipListSet<>(); | |||
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Don't love the visibility of this, but we needed access from the migration task. Will probably update the task itself to hold a reference to this.
| * Don't request schema from bootstrapping nodes (?) | ||
| * Don't request schema if we have scheduled a pull request for that schema version | ||
| */ | ||
| boolean isOtherSchemaNonEmpty = !Schema.emptyVersion.equals(theirVersion); |
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This is an additional check to prevent making schema pull requests to new nodes. It's probably not that important, since the work done in response to that is pretty small.
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Reduce schema pull request volume by only scheduling one request per schema version at a time. The thought is that any successful request for a schema version will return the same set of mutations, so there's no need to flood other nodes with unnecessary requests.