DiskLoc RecordStoreV1Base::_findFirstSpot( OperationContext* txn,
const DiskLoc& extDiskLoc, Extent* e ) {
DiskLoc emptyLoc = extDiskLoc;
emptyLoc.inc( Extent::HeaderSize() );
int delRecLength = e->length - Extent::HeaderSize();
if ( delRecLength >= 32*1024 && _ns.find('$') != string::npos && !isCapped() ) {
// probably an index. so skip forward to keep its records page aligned
int& ofs = emptyLoc.GETOFS();
int newOfs = (ofs + 0xfff) & ~0xfff;
delRecLength -= (newOfs-ofs);
dassert( delRecLength > 0 );
ofs = newOfs;
}
DeletedRecord* empty = txn->recoveryUnit()->writing(drec(emptyLoc));
empty->lengthWithHeaders() = delRecLength;
empty->extentOfs() = e->myLoc.getOfs();
empty->nextDeleted().Null();
return emptyLoc;
}
DiskLoc SimpleRecordStoreV1::_allocFromExistingExtents( OperationContext* txn,
int lenToAlloc ) {
// align size up to a multiple of 4
lenToAlloc = (lenToAlloc + (4-1)) & ~(4-1);
freelistAllocs.increment();
DiskLoc loc;
{
DiskLoc *prev = 0;
DiskLoc *bestprev = 0;
DiskLoc bestmatch;
int bestmatchlen = INT_MAX; // sentinel meaning we haven't found a record big enough
int b = bucket(lenToAlloc);
DiskLoc cur = _details->deletedListEntry(b);
int extra = 5; // look for a better fit, a little.
int chain = 0;
while ( 1 ) {
{ // defensive check
int fileNumber = cur.a();
int fileOffset = cur.getOfs();
if (fileNumber < -1 || fileNumber >= 100000 || fileOffset < 0) {
StringBuilder sb;
sb << "Deleted record list corrupted in collection " << _ns
<< ", bucket " << b
<< ", link number " << chain
<< ", invalid link is " << cur.toString()
<< ", throwing Fatal Assertion";
log() << sb.str() << endl;
fassertFailed(16469);
}
}
if ( cur.isNull() ) {
// move to next bucket. if we were doing "extra", just break
if ( bestmatchlen < INT_MAX )
break;
if ( chain > 0 ) {
// if we looked at things in the right bucket, but they were not suitable
freelistBucketExhausted.increment();
}
b++;
if ( b > MaxBucket ) {
// out of space. alloc a new extent.
freelistIterations.increment( 1 + chain );
return DiskLoc();
}
cur = _details->deletedListEntry(b);
prev = 0;
continue;
}
DeletedRecord *r = drec(cur);
if ( r->lengthWithHeaders() >= lenToAlloc &&
r->lengthWithHeaders() < bestmatchlen ) {
bestmatchlen = r->lengthWithHeaders();
bestmatch = cur;
bestprev = prev;
if (r->lengthWithHeaders() == lenToAlloc)
// exact match, stop searching
break;
}
if ( bestmatchlen < INT_MAX && --extra <= 0 )
break;
if ( ++chain > 30 && b <= MaxBucket ) {
// too slow, force move to next bucket to grab a big chunk
//b++;
freelistIterations.increment( chain );
chain = 0;
cur.Null();
}
else {
cur = r->nextDeleted();
prev = &r->nextDeleted();
}
}
// unlink ourself from the deleted list
DeletedRecord *bmr = drec(bestmatch);
if ( bestprev ) {
*txn->recoveryUnit()->writing(bestprev) = bmr->nextDeleted();
}
else {
// should be the front of a free-list
int myBucket = bucket(bmr->lengthWithHeaders());
invariant( _details->deletedListEntry(myBucket) == bestmatch );
_details->setDeletedListEntry(txn, myBucket, bmr->nextDeleted());
}
*txn->recoveryUnit()->writing(&bmr->nextDeleted()) = DiskLoc().setInvalid(); // defensive.
invariant(bmr->extentOfs() < bestmatch.getOfs());
freelistIterations.increment( 1 + chain );
loc = bestmatch;
}
if ( loc.isNull() )
return loc;
// determine if we should chop up
DeletedRecord *r = drec(loc);
/* note we want to grab from the front so our next pointers on disk tend
to go in a forward direction which is important for performance. */
int regionlen = r->lengthWithHeaders();
invariant( r->extentOfs() < loc.getOfs() );
int left = regionlen - lenToAlloc;
if ( left < 24 || left < (lenToAlloc / 8) ) {
// you get the whole thing.
return loc;
}
// don't quantize:
// - $ collections (indexes) as we already have those aligned the way we want SERVER-8425
if ( _normalCollection ) {
// we quantize here so that it only impacts newly sized records
// this prevents oddities with older records and space re-use SERVER-8435
lenToAlloc = std::min( r->lengthWithHeaders(),
quantizeAllocationSpace( lenToAlloc ) );
left = regionlen - lenToAlloc;
if ( left < 24 ) {
// you get the whole thing.
return loc;
}
}
/* split off some for further use. */
txn->recoveryUnit()->writingInt(r->lengthWithHeaders()) = lenToAlloc;
DiskLoc newDelLoc = loc;
newDelLoc.inc(lenToAlloc);
DeletedRecord* newDel = drec(newDelLoc);
DeletedRecord* newDelW = txn->recoveryUnit()->writing(newDel);
newDelW->extentOfs() = r->extentOfs();
newDelW->lengthWithHeaders() = left;
newDelW->nextDeleted().Null();
addDeletedRec( txn, newDelLoc );
return loc;
}