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Fix it, then Ship it! LGTM. A couple of smaller points below, with the largest being the somewhat blurry handling of time-based executions. src/main/java/org/apache/aurora/scheduler/BatchWorker.java (line 197) <https://reviews.apache.org/r/51759/#comment216434> `readyItems` is still a left over from the previous patch version. Could be renamed to just `batch`. src/main/java/org/apache/aurora/scheduler/BatchWorker.java (line 228) <https://reviews.apache.org/r/51759/#comment216435> Do you have any particular usecase for this metric? We already have `batchesProcessed` and `itemsProcessed` and can compute the rate of processed items and batches. This seems more robust to me than just looking at `lastBatchSize`. src/main/java/org/apache/aurora/scheduler/scheduling/TaskThrottler.java (lines 73 - 87) <https://reviews.apache.org/r/51759/#comment216437> This code is exposing a slight design smell in my eye: We are using the `DelayedExecutor` to trigger the `batchWorker` when a backoff timer has passed. However, the latter already provides an internal backoff mechanism. I'd rather see if we have just one defined way how to handle those time-based backoffs: * either the BatchWorker does not perform any backoff handling at all. This seems to be in line with what Zameer has proposed in his last comment, * or we make the backoff mechanism a first-class feature of the batchWorker so that I can say I can inject `backoffStrategy` and `lastBackoffMsec` to be used for the `WorkItem` created in `batchWorker.execute`. - Stephan Erb On Sept. 14, 2016, 6:47 p.m., Maxim Khutornenko wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > https://reviews.apache.org/r/51759/ > ----------------------------------------------------------- > > (Updated Sept. 14, 2016, 6:47 p.m.) > > > Review request for Aurora, Joshua Cohen, Stephan Erb, and Zameer Manji. > > > Repository: aurora > > > Description > ------- > > This is the first (out of 3) patches intending to reduce storage write lock > contention and as such improve overall system write throughput. It introduces > the `BatchWorker` and migrates the majority of storage writes due to task > status change events to use `TaskEventBatchWorker`. > > #####Problem > Our current storage system writes effectively behave as `SERIALIZABLE` > transaction isolation level in SQL terms. This means all writes require > exclusive access to the storage and no two transactions can happen in > parallel [1]. While it certainly simplifies our implementation, it creates a > single hotspot where multiple threads are competing for the storage write > access. This type of contention only worsens as the cluster size grows, more > tasks are scheduled, more status updates are processed, more subscribers are > listening to status updates and etc. Eventually, the scheduler throughput > (and especially task scheduling) becomes degraded to the extent that certain > operations wait much longer (4x and more) for the lock acquisition than it > takes to process their payload when inside the transaction. Some ops (like > event processing) are generally tolerant of these types of delays. Others - > not as much. The task scheduling suffers the most as backing up the > scheduling queue directly affects the Median Time To Assigned (MTTA). > > #####Remediation > Given the above, it's natural to assume that reducing the number of write > transactions should help reducing the lock contention. This patch introduces > a generic `BatchWorker` service that delivers a "best effort" batching > approach by redirecting multiple individual write requests into a single FIFO > queue served non-stop by a single dedicated thread. Every batch shares a > single write transaction thus reducing the number of potential write lock > requests. To minimize wait-in-queue time, items are dispatched immediately > and the max number of items is bounded. There are a few `BatchWorker` > instances specialized on particular workload types: task even processing, > cron scheduling and task scheduling. Every instance can be tuned > independently (max batch size) and provides specialized metrics helping to > monitor each workload type perf. > > #####Results > The proposed approach has been heavily tested in production and delivered the > best results. The lock contention latencies got down between 2x and 5x > depending on the cluster load. A number of other approaches tried but > discarded as not performing well or even performing much worse than the > current master: > - Clock-driven batch execution - every batch is dispatched on a time schedule > - Max batch with a deadline - a batch is dispatched when max size is reached > OR a timeout expires > - Various combinations of the above - some `BatchWorkers` are using > clock-driven execution while others are using max batch with a deadline > - Completely non-blocking (event-based) completion notification - all call > sites are notified of item completion via a `BatchWorkCompleted` event > > Happy to provide more details on the above if interested. > > #####Upcoming > The introduction of the `BatchWorker` by itself was not enough to > substantially improve the MTTA. It, however, paves the way for the next phase > of scheduling perf improvement - taking more than 1 task from a given > `TaskGroup` in a single scheduling round (coming soon). That improvement > wouldn't deliver without decreasing the lock contention first. > > Note: it wasn't easy to have a clean diff split, so some functionality in > `BatchWorker` (e.g.: `executeWithReplay`) appears to be unused in the current > patch but will become obvious in the part 2 (coming out shortly). > > [1] - > https://github.com/apache/aurora/blob/f6ac13b169aaad5aad73ef3cc72873781e30a705/src/main/java/org/apache/aurora/scheduler/storage/log/LogStorage.java#L540-L555 > > > Diffs > ----- > > src/main/java/org/apache/aurora/scheduler/BatchWorker.java PRE-CREATION > src/main/java/org/apache/aurora/scheduler/SchedulerModule.java > 4a7ef0b1b90607f68d89fe8e207f42c42a8c56a0 > src/main/java/org/apache/aurora/scheduler/pruning/TaskHistoryPruner.java > f07746c2b990c1c2235e99f9e4775fc84f9c27b1 > src/main/java/org/apache/aurora/scheduler/scheduling/TaskThrottler.java > bbd971a2aa8a96cf79edd879ad60e1bebd933d79 > src/main/java/org/apache/aurora/scheduler/state/MaintenanceController.java > 3c7cda09ab292d696070ca4d9dfedb1f6f71b0fe > > src/main/java/org/apache/aurora/scheduler/updater/JobUpdateControllerImpl.java > 594bb6219294dcc77d48dcad14e2a6f9caa0c534 > src/test/java/org/apache/aurora/scheduler/BatchWorkerTest.java PRE-CREATION > > src/test/java/org/apache/aurora/scheduler/pruning/TaskHistoryPrunerTest.java > 99c27e8012f10a67ce5f1b84d258e7a5608995c7 > src/test/java/org/apache/aurora/scheduler/scheduling/TaskThrottlerTest.java > 7d104aa2ea4a4d99be4711f666d18beca238284e > > src/test/java/org/apache/aurora/scheduler/state/MaintenanceControllerImplTest.java > 94f5ca565476f62d72879837a0e7dafabcf30432 > src/test/java/org/apache/aurora/scheduler/testing/BatchWorkerUtil.java > PRE-CREATION > src/test/java/org/apache/aurora/scheduler/updater/JobUpdaterIT.java > 196df4754b553f05e50b66ad2f84271901bc9eba > > Diff: https://reviews.apache.org/r/51759/diff/ > > > Testing > ------- > > All types of testing including deploying to test and production clusters. > > > Thanks, > > Maxim Khutornenko > >
