// prefetch for an oplog operation
void prefetchPagesForReplicatedOp(OperationContext* txn,
Database* db,
const repl::ReplSetImpl::IndexPrefetchConfig& prefetchConfig,
const BSONObj& op) {
const char *opField;
const char *opType = op.getStringField("op");
switch (*opType) {
case 'i': // insert
case 'd': // delete
opField = "o";
break;
case 'u': // update
opField = "o2";
break;
default:
// prefetch ignores other ops
return;
}
BSONObj obj = op.getObjectField(opField);
const char *ns = op.getStringField("ns");
Collection* collection = db->getCollection( txn, ns );
if ( !collection )
return;
LOG(4) << "index prefetch for op " << *opType << endl;
DEV txn->lockState()->assertAtLeastReadLocked(ns);
// should we prefetch index pages on updates? if the update is in-place and doesn't change
// indexed values, it is actually slower - a lot slower if there are a dozen indexes or
// lots of multikeys. possible variations (not all mutually exclusive):
// 1) current behavior: full prefetch
// 2) don't do it for updates
// 3) don't do multikey indexes for updates
// 4) don't prefetchIndexPages on some heuristic; e.g., if it's an $inc.
// 5) if not prefetching index pages (#2), we should do it if we are upsertings and it
// will be an insert. to do that we could do the prefetchRecordPage first and if DNE
// then we do #1.
//
// note that on deletes 'obj' does not have all the keys we would want to prefetch on.
// a way to achieve that would be to prefetch the record first, and then afterwards do
// this part.
//
prefetchIndexPages(collection, prefetchConfig, obj);
// do not prefetch the data for inserts; it doesn't exist yet
//
// we should consider doing the record prefetch for the delete op case as we hit the record
// when we delete. note if done we only want to touch the first page.
//
// update: do record prefetch.
if ((*opType == 'u') &&
// do not prefetch the data for capped collections because
// they typically do not have an _id index for findById() to use.
!collection->isCapped()) {
prefetchRecordPages(txn, ns, obj);
}
}
// prefetch for an oplog operation
void prefetchPagesForReplicatedOp(OperationContext* opCtx,
Database* db,
const OplogEntry& oplogEntry) {
invariant(db);
const ReplSettings::IndexPrefetchConfig prefetchConfig =
ReplicationCoordinator::get(opCtx)->getIndexPrefetchConfig();
// Prefetch ignores non-CRUD operations.
if (!oplogEntry.isCrudOpType()) {
return;
}
// This will have to change for engines other than MMAP V1, because they might not have
// means for directly prefetching pages from the collection. For this purpose, acquire S
// lock on the database, instead of optimizing with IS.
const auto& nss = oplogEntry.getNamespace();
Lock::CollectionLock collLock(opCtx->lockState(), nss.ns(), MODE_S);
Collection* collection = db->getCollection(opCtx, nss);
if (!collection) {
return;
}
auto opType = oplogEntry.getOpType();
LOG(4) << "index prefetch for op " << OpType_serializer(opType);
// should we prefetch index pages on updates? if the update is in-place and doesn't change
// indexed values, it is actually slower - a lot slower if there are a dozen indexes or
// lots of multikeys. possible variations (not all mutually exclusive):
// 1) current behavior: full prefetch
// 2) don't do it for updates
// 3) don't do multikey indexes for updates
// 4) don't prefetchIndexPages on some heuristic; e.g., if it's an $inc.
// 5) if not prefetching index pages (#2), we should do it if we are upsertings and it
// will be an insert. to do that we could do the prefetchRecordPage first and if DNE
// then we do #1.
//
// note that on deletes 'obj' does not have all the keys we would want to prefetch on.
// a way to achieve that would be to prefetch the record first, and then afterwards do
// this part.
//
auto obj = oplogEntry.getOperationToApply();
invariant(!obj.isEmpty());
prefetchIndexPages(opCtx, collection, prefetchConfig, obj);
// do not prefetch the data for inserts; it doesn't exist yet
//
// we should consider doing the record prefetch for the delete op case as we hit the record
// when we delete. note if done we only want to touch the first page.
//
// update: do record prefetch.
if ((opType == OpTypeEnum::kUpdate) &&
// do not prefetch the data for capped collections because
// they typically do not have an _id index for findById() to use.
!collection->isCapped()) {
prefetchRecordPages(opCtx, db, nss.ns().c_str(), obj);
}
}