Details
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Improvement
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Status: Closed
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Major - P3
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Resolution: Fixed
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None
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None
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None
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Fully Compatible
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Execution Team 2022-05-16
Description
Currently we do a separate atomic increment on _nextIdNum for each document in a batch. In addition to doing significantly more atomic ops than is necessary, it risks other concurrent inserts grabbing interleaving ids rather than having a nice contiguous range for this batch. I suspect this could lead to increased contention inside WT vs each thread having a private range to play in. This would also stack nicely with SERVER-55337 and SERVER-55338
Instead we should increment _nextIdNum once by the number of documents in the batch, and then hand out ids from a local counter. Possible patch:
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.cpp
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index 1fca344df7..93c5702e40 100644
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--- a/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.cpp
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+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.cpp
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@@ -1536,6 +1536,7 @@ Status WiredTigerRecordStore::_insertRecords(OperationContext* opCtx,
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Record highestIdRecord;
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invariant(nRecords != 0);
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+ auto recIdGen = _isOplog ? RecordId() : _nextId(opCtx, nRecords);
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for (size_t i = 0; i < nRecords; i++) {
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auto& record = records[i];
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if (_isOplog) {
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@@ -1545,7 +1546,8 @@ Status WiredTigerRecordStore::_insertRecords(OperationContext* opCtx,
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return status.getStatus();
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record.id = status.getValue();
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} else {
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- record.id = _nextId(opCtx);
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+ record.id = recIdGen;
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+ recIdGen = RecordId(recIdGen.as<int64_t>() + 1);
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}
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dassert(record.id > highestIdRecord.id);
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highestIdRecord = record;
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@@ -2029,10 +2031,10 @@ void WiredTigerRecordStore::_initNextIdIfNeeded(OperationContext* opCtx) {
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_nextIdNum.store(nextId);
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}
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-RecordId WiredTigerRecordStore::_nextId(OperationContext* opCtx) {
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+RecordId WiredTigerRecordStore::_nextId(OperationContext* opCtx, int64_t numIds) {
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invariant(!_isOplog);
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_initNextIdIfNeeded(opCtx);
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- RecordId out = RecordId(_nextIdNum.fetchAndAdd(1));
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+ RecordId out = RecordId(_nextIdNum.fetchAndAdd(numIds));
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invariant(out.isNormal());
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return out;
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}
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diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.h b/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.h
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index 85275dca25..1fd2131a9d 100644
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--- a/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.h
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+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.h
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@@ -294,7 +294,7 @@ class WiredTigerRecordStore : public RecordStore {
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const Timestamp* timestamps,
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size_t nRecords);
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- RecordId _nextId(OperationContext* opCtx);
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+ RecordId _nextId(OperationContext* opCtx, int64_t numIds = 1);
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bool cappedAndNeedDelete() const;
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RecordData _getData(const WiredTigerCursor& cursor) const; |
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