RATIS-2430. Write snapshot to temporary path until finish#1372
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spacemonkd wants to merge 2 commits into
Open
RATIS-2430. Write snapshot to temporary path until finish#1372spacemonkd wants to merge 2 commits into
spacemonkd wants to merge 2 commits into
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@szetszwo could you take a look at this change? |
szetszwo
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Jun 11, 2026
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@spacemonkd , thanks for working on this! Please see the comments inlined and also https://issues.apache.org/jira/secure/attachment/13082753/1372_review.patch
(Sorry that I missed this PR.)
| void finalizeSnapshot(InstallSnapshotRequestProto request) throws IOException { | ||
| final StateMachine sm = server.getStateMachine(); | ||
| sm.pause(); // pause the SM right before publishing the snapshot atomically | ||
| // TODO: if there is a failure here, we need to rollback the snapshot installation. |
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What do you mean by "rollback the snapshot installation" ?
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| final int expectedChunkIndex = nextChunkIndex.get(); | ||
| if (expectedChunkIndex != snapshotChunkRequest.getRequestIndex()) { | ||
| throw new IOException("Unexpected request chunk index: " + snapshotChunkRequest.getRequestIndex() | ||
| + " (the expected index is " + expectedChunkIndex + ")"); | ||
| } | ||
| // Append chunks to a temporary location first. Publish only when done=true. | ||
| state.appendSnapshot(request); | ||
| nextChunkIndex.incrementAndGet(); | ||
| // update the committed index | ||
| // re-load the state machine if this is the last chunk | ||
| if (snapshotChunkRequest.getDone()) { | ||
| state.finalizeSnapshot(request); | ||
| state.reloadStateMachine(lastIncluded); | ||
| chunk0CallId.set(-1); |
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Let's move snapshotManager to SnapshotInstallationHandler. It is only used here.
final int expectedChunkIndex = nextChunkIndex.get();
if (expectedChunkIndex != snapshotChunkRequest.getRequestIndex()) {
throw new IOException("Unexpected request chunk index: " + snapshotChunkRequest.getRequestIndex()
+ " (the expected index is " + expectedChunkIndex + ")");
}
// Append chunks to a temporary location first. Publish only when done=true.
final StateMachine stateMachine = server.getStateMachine();
snapshotManager.appendSnapshot(request, stateMachine);
nextChunkIndex.incrementAndGet();
// update the committed index
// re-load the state machine if this is the last chunk
if (snapshotChunkRequest.getDone()) {
stateMachine.pause(); // pause the SM right before publishing the snapshot atomically
snapshotManager.finalizeSnapshot(request);
state.reloadStateMachine(lastIncluded);
chunk0CallId.set(-1);
}
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| if (!snapshotChunkRequest.getDone()) { | ||
| throw new IOException("Cannot finalize incomplete snapshot request: " | ||
| + ServerStringUtils.toInstallSnapshotRequestString(request)); | ||
| } |
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Let's use Preconditions:
Preconditions.assertTrue(snapshotChunkRequest.getDone());| import static org.mockito.Mockito.mock; | ||
| import static org.mockito.Mockito.when; | ||
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| public class SnapshotManagerTest { |
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To be consistent with the other tests,
- rename it to "TestSnapshotManager"
- move it to ratis-test.
| import static org.mockito.Mockito.when; | ||
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| public class SnapshotManagerTest { | ||
| private static final class TestRaftStorageDirectory implements RaftStorageDirectory { |
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Let's use RaftStorageDirectoryImpl.
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What changes were proposed in this pull request?
Today when SnapshotInstallatioHandler#checkAndInstallSnapshot calls
state.installSnapshot(request)- it pauses the state machine viaServerState.installSnapshot().However this means that in case later checks fail or IO fails or any such scenario occurs, then there is no clear rollback option. Followers in this scenario can be left in a partial installation state.
One way to mitigate this is in appendChunk we can write to a temp file without pausing StateMachine. When this is done we can atomically apply the snapshot and reload the statemachine log.
What is the link to the Apache JIRA
https://issues.apache.org/jira/browse/RATIS-2430
How was this patch tested?
Patch was tested using unit tests.