Improve proxy GRV latencies and responsiveness #2735
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…ve performance and increase responsiveness to changes in workload.
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An example of the type of performance improvement: When running a test at about 90% of ratekeeper's limit, the new algorithm had 99th percentile latencies around 1-2ms, while the old algorithm was around 75ms. |
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This is quite clever and I think this should be strictly better than the old mechanism. However I would like to see some comments as in order to understand this one has to read through quite a lot of code.
I would also suggest you add your explanation that you put into this PR as a comment into the code. Maybe on top of TransactionRateInfo? That will make it a lot easier to understand this in the future.
| break; | ||
| } else if (req.priority() < GetReadVersionRequest::PRIORITY_SYSTEM_IMMEDIATE && | ||
| !normalRateInfo.canStart(transactionsStarted[0] + transactionsStarted[1])) { | ||
| if(req.priority() < GetReadVersionRequest::PRIORITY_DEFAULT && !batchRateInfo.canStart(transactionsStarted[0] + transactionsStarted[1], tc)) { |
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It seems this PR has not applied clang-format.
I also saw some trailing space after checking it out locally.
Would you mind clang-formatting the change?
…y-perf-improvements # Conflicts: # fdbserver/Knobs.cpp # fdbserver/Knobs.h # fdbserver/MasterProxyServer.actor.cpp
This changes the algorithm used to decide whether a proxy can respond to a start request. The previous algorithm was prone to introducing unneeded latency as the request rate went up, and it could be very slow to respond to changes in workload that would allow lower priority work to start.
The new algorithm has the proxy tracking a smoothed rate for how many transactions can be started and how many have been started, permitting transactions to be started if the rate difference times some time window is larger than the number to be started. It also keeps a budget to allow it to start transaction batches that are larger than can be handled by the windowed mechanism.
Resolves #2206