-question about the scanner ordering for gets/scans
Sergey Shelukhin 2013-01-31, 00:44
Hi. When we build the scanner for scan or get, we make sure to add scanners
in sorted order.
// First the store file scanners
> // TODO this used to get the store files in descending order,
> // but now we get them in ascending order, which I think is
> // actually more correct, since memstore get put at the end.
> List<StoreFileScanner> sfScanners = StoreFileScanner
> .getScannersForStoreFiles(storeFilesToScan, cacheBlocks, isGet,
> isCompaction, matcher);
> List<KeyValueScanner> scanners > new ArrayList<KeyValueScanner>(sfScanners.size()+1);
> // Then the memstore scanners
I have read the code for scanning/around this area and have a question,
does order of scanners actually matter? It looks like we insert them into
heap structure and seek/peek them all anyway, and compare separately by
seqNum in KeyValueHeap::KVScannerComparator.
Is sorting really needed for this particular place (above code)?