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Fixing transaction_timed_out errors with long running reads. #182

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merged 4 commits into from
Apr 26, 2019
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Fixing transaction_timed_out errors with long running reads. #182

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da7ff49
Fixing transaction_timed_out errors with long running reads.
apkar Apr 25, 2019
90c209f
Update src/QLPlan.actor.cpp
alexmiller-apple Apr 26, 2019
d48fd25
Use `g_network->getCurrentTask() + 1` instead of `TaskMaxPriority` for
apkar Apr 26, 2019
bd002d1
Merge branch 'read_timeouts' of github.com:apkar/fdb-document-layer i…
apkar Apr 26, 2019
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56 changes: 37 additions & 19 deletions src/QLPlan.actor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -687,38 +687,58 @@ ACTOR static Future<Void> doNonIsolatedRO(PlanCheckpoint* outerCheckpoint,
Reference<MetadataManager> mm) {
if (!dtr)
dtr = self->newTransaction();
state double startt = now();
state Reference<PlanCheckpoint> innerCheckpoint(new PlanCheckpoint);
state int nTransactions = 1;
state int64_t nResults = 0;
state FlowLock* outerLock = outerCheckpoint->getDocumentFinishedLock();
state Deque<std::pair<Reference<ScanReturnedContext>, Future<Void>>> bufferedDocs;

try {
state uint64_t metadataVersion = wait(cx->bindCollectionContext(dtr)->getMetadataVersion());
loop {
state FutureStream<Reference<ScanReturnedContext>> docs = subPlan->execute(innerCheckpoint.getPtr(), dtr);
state FlowLock* innerLock = innerCheckpoint->getDocumentFinishedLock();
state bool first = true;
state Future<Void> timeout = delay(3.0);
state Future<Void> timeout = delay(3.0, TaskMaxPriority);
state bool finished = false;

loop choose {
when(state Reference<ScanReturnedContext> doc = waitNext(docs)) {
// throws end_of_stream when totally finished
Void _ = wait(outerLock->take());
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Would it be equivalent and simpler to just do Void _ = wait( outerLock->take() || timeout ); instead of splitting this into two functions?

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@apkar apkar Apr 26, 2019 •
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If I am thinking right, it would look like this

loop choose {
	when(state Reference<ScanReturnedContext> doc = waitNext(docs)) {
	// throws end_of_stream when totally finished
		Void _ = wait(outerLock->take() || timeout);
		if (!timeout.isReady()) {
                       .....
		}
	}
	when(Void _ = wait(timeout)) { break; }
}

// squeeze remaining documents from the stream

// checkpoint planner

This will need special handling with !timeout.isReady().

And due to the way query planner checkpoint scheme works, it's important there are no documents pending in document stream when the checkpoint is being called, that would be below this loop. I guess I can have extra code before the checkpoint to squeeze the documents left in the stream.

If so, probably having 3 when blocks probably clearer code.

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innerLock->release();
output.send(doc);
++nResults;
if (first) {
timeout = delay(DOCLAYER_KNOBS->NONISOLATED_INTERNAL_TIMEOUT);
first = false;
try {
loop choose {
when(Reference<ScanReturnedContext> doc = waitNext(docs)) {
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What is the priority at which this stream is yielding results?

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Doc Layer code that is sending documents to this stream is not setting any priority explicitly. Source of the data is FDB flow bindings. Flow bindings set the priority to TaskDefaultOnMainThread (7500) and delay default priority is TaskDefaultDelay (7010). I tried this with TaskProxyGRVTimer (8510) instead of max priority, that too seems to be fixing the issue. Shall I go with it?

// throws end_of_stream when totally finished
bufferedDocs.push_back(std::make_pair(doc, outerLock->take()));
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Do you need to pass a priority to take() as well?

}
when(Void _ = wait(bufferedDocs.empty() ? Never() : bufferedDocs.front().second)) {
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You're taking outerLock, but releasing innerLock, so what's making sure that you actually process documents as you add them?

innerLock->release();
output.send(bufferedDocs.front().first);
bufferedDocs.pop_front();
++nResults;
if (first) {
timeout = delay(DOCLAYER_KNOBS->NONISOLATED_INTERNAL_TIMEOUT, TaskMaxPriority);
first = false;
}
}
when(Void _ = wait(timeout)) { break; }
}
when(Void _ = wait(timeout)) { break; }
ASSERT(!docs.isReady());
} catch (Error& e) {
if (e.code() != error_code_end_of_stream)
throw e;
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finished = true;
}

ASSERT(!docs.isReady());

innerCheckpoint = innerCheckpoint->stopAndCheckpoint();

while (!bufferedDocs.empty()) {
Void _ = wait(bufferedDocs.front().second);
output.send(bufferedDocs.front().first);
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Do you not need to innerLock->release(); here also?

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Because of checkpoint at line 730, innerLock is not valid anymore, no one is waiting on it.

bufferedDocs.pop_front();
++nResults;
}

if (finished)
throw end_of_stream();

dtr = self->newTransaction();
state uint64_t newMetadataVersion = wait(cx->bindCollectionContext(dtr)->getMetadataVersion());
if (newMetadataVersion != metadataVersion) {
Expand Down Expand Up @@ -763,7 +783,7 @@ ACTOR static Future<Void> doNonIsolatedRW(PlanCheckpoint* outerCheckpoint,
state FlowLock* innerLock = innerCheckpoint->getDocumentFinishedLock();
state bool first = true;
state bool finished = false;
state Future<Void> timeout = delay(3.0);
state Future<Void> timeout = delay(3.0, TaskMaxPriority);
state Deque<std::pair<Reference<ScanReturnedContext>, Future<Void>>> committingDocs;
state Deque<Reference<ScanReturnedContext>> bufferedDocs;

Expand All @@ -781,7 +801,7 @@ ACTOR static Future<Void> doNonIsolatedRW(PlanCheckpoint* outerCheckpoint,
waitNext(docs)) { // throws end_of_stream when totally finished
committingDocs.push_back(std::make_pair(doc, doc->commitChanges()));
if (first) {
timeout = delay(DOCLAYER_KNOBS->NONISOLATED_INTERNAL_TIMEOUT);
timeout = delay(DOCLAYER_KNOBS->NONISOLATED_INTERNAL_TIMEOUT, TaskMaxPriority);
first = false;
}
}
Expand Down Expand Up @@ -1148,10 +1168,8 @@ ACTOR static Future<Void> findAndModify(PlanCheckpoint* outerCheckpoint,
PromiseStream<Reference<ScanReturnedContext>> output) {
if (!dtr)
dtr = NonIsolatedPlan::newTransaction(database);
state double startt = now();
state Reference<PlanCheckpoint> innerCheckpoint(new PlanCheckpoint);
state int nTransactions = 1;
state int64_t nResults = 0;
state FlowLock* outerLock = outerCheckpoint->getDocumentFinishedLock();
state Reference<ScanReturnedContext> firstDoc;
state bool any = false;
Expand Down