Plan queue apply overlaps plan verification with plan application to increase throughput #272
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| // Naively, we could simply dequeue a plan, verify, apply and then respond. | ||
| // However, the plan application is bounded by the Raft apply time and | ||
| // subject to some latency. This creates a stall condition, where we are | ||
| // not evaluating, but simply waiting for a transaction to complete. |
armon
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Oct 12, 2015
Plan queue apply overlaps plan verification with plan application to increase throughput
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I'm going to lock this pull request because it has been closed for 120 days ⏳. This helps our maintainers find and focus on the active contributions. |
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The plan apply would previously always do dequeue, verify, apply, respond. This meant that the time spent in apply which is just waiting for a Raft commit would prevent any other verification from happening.
Now, the plan does dequeue and verify, and then does an async apply and respond. While we are waiting for the plan to apply, we optimistically apply the plan to a snapshot of state and begin verifying the next plan. This allows us to overlap the application with the verification to reduce the amount of time spent waiting.
This PR supports only a single level of overlap (apply N, verify N+1), but it can be extended in the future to support K levels of verify-ahead (apply N, verify N+1, ..., verify N+K).