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Type:
Improvement
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Resolution: Fixed
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Priority:
Major - P3
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Affects Version/s: None
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Component/s: None
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None
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Fully Compatible
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Execution Team 2022-05-16
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
index 1fca344df7..93c5702e40 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.cpp
@@ -1536,6 +1536,7 @@ Status WiredTigerRecordStore::_insertRecords(OperationContext* opCtx,
Record highestIdRecord;
invariant(nRecords != 0);
+ auto recIdGen = _isOplog ? RecordId() : _nextId(opCtx, nRecords);
for (size_t i = 0; i < nRecords; i++) {
auto& record = records[i];
if (_isOplog) {
@@ -1545,7 +1546,8 @@ Status WiredTigerRecordStore::_insertRecords(OperationContext* opCtx,
return status.getStatus();
record.id = status.getValue();
} else {
- record.id = _nextId(opCtx);
+ record.id = recIdGen;
+ recIdGen = RecordId(recIdGen.as<int64_t>() + 1);
}
dassert(record.id > highestIdRecord.id);
highestIdRecord = record;
@@ -2029,10 +2031,10 @@ void WiredTigerRecordStore::_initNextIdIfNeeded(OperationContext* opCtx) {
_nextIdNum.store(nextId);
}
-RecordId WiredTigerRecordStore::_nextId(OperationContext* opCtx) {
+RecordId WiredTigerRecordStore::_nextId(OperationContext* opCtx, int64_t numIds) {
invariant(!_isOplog);
_initNextIdIfNeeded(opCtx);
- RecordId out = RecordId(_nextIdNum.fetchAndAdd(1));
+ RecordId out = RecordId(_nextIdNum.fetchAndAdd(numIds));
invariant(out.isNormal());
return out;
}
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.h b/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.h
index 85275dca25..1fd2131a9d 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.h
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.h
@@ -294,7 +294,7 @@ class WiredTigerRecordStore : public RecordStore {
const Timestamp* timestamps,
size_t nRecords);
- RecordId _nextId(OperationContext* opCtx);
+ RecordId _nextId(OperationContext* opCtx, int64_t numIds = 1);
bool cappedAndNeedDelete() const;
RecordData _getData(const WiredTigerCursor& cursor) const;
- is related to
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- Backlog
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- Backlog
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