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Code Issues Releases Wiki Activity

Fix conflicts between locks (#2407)

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Use REPEATABLE READ for lock acquire/release operation to avoid conlicts
between locks.

Postgresql uses table scan on small tables, causing false sharing at
the SERIALIZABLE isolation level.

See b/333537928 for details.
This commit is contained in:
Weimin Yu
2024-04-24 14:51:18 -04:00
committed by GitHub
parent 6d0a746b76
commit 9c443bede1
1 changed files with 17 additions and 2 deletions
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19
core/src/main/java/google/registry/model/server/Lock.java
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@@ -15,6 +15,7 @@
package google.registry.model.server;
import static com.google.common.base.Preconditions.checkArgument;
import static google.registry.persistence.PersistenceModule.TransactionIsolationLevel.TRANSACTION_REPEATABLE_READ;
import static google.registry.persistence.transaction.TransactionManagerFactory.tm;
import static google.registry.util.DateTimeUtils.isAtOrAfter;
import static google.registry.util.PreconditionsUtils.checkArgumentNotNull;
@@ -196,7 +197,20 @@ public class Lock extends ImmutableObject implements Serializable {
return new AcquireResult(now, lock, newLock, lockState);
};
AcquireResult acquireResult = tm().transact(lockAcquirer);
/*
* Use REPEATABLE READ to avoid write conflicts with other locks.
*
* <p>Since the Lock table is small, Postgresql may choose table scan instead of PK lookup. At
* the SERIALIZABLE level this can cause conflicts with other locks. There is no way to forbid
* table scan on a per-query or per-table basis.
*
* <p>Using REPEATABLE READ is safe since Lock acquire/release only accesses one row. Note that
* passing the isolation level to the `transact` method requires that it is not a nested
* transaction. As of the time of this change this is the case.
*
* <p>See b/333537928 for more information.
*/
AcquireResult acquireResult = tm().transact(TRANSACTION_REPEATABLE_READ, lockAcquirer);
logAcquireResult(acquireResult);
lockMetrics.recordAcquire(resourceName, scope, acquireResult.lockState());
@@ -232,7 +246,8 @@ public class Lock extends ImmutableObject implements Serializable {
"Not deleting lock: %s - someone else has it: %s", lockId, loadedLock);
}
};
tm().transact(lockReleaser);
// See comments in the `acquire` method for this isolation level.
tm().transact(TRANSACTION_REPEATABLE_READ, lockReleaser);
}
static class LockId extends ImmutableObject implements Serializable {