Why HBase scan HFile first, before scan memstore?

[Xi Yang]

I found codes in HStore.java

List<StoreFileScanner> sfScanners =
StoreFileScanner.getScannersForStoreFiles(files,
      cacheBlocks, usePread, isCompaction, false, matcher, readPt,
isPrimaryReplicaStore());
    List<KeyValueScanner> scanners = new
ArrayList<KeyValueScanner>(sfScanners.size() + 1);
    scanners.addAll(sfScanners);
    // Then the memstore scanners
    if (memStoreScanners != null) {
      scanners.addAll(memStoreScanners);
    }

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So is it mean before scan memstore it will scan HFile first?
Why not scan memstore first, because memory is always faster then hard disk?


Thanks,
Alex