/**
* Pretend we have done a seek but don't do it yet, if possible. The hope is that we find
* requested columns in more recent files and won't have to seek in older files. Creates a fake
* key/value with the given row/column and the highest (most recent) possible timestamp we might
* get from this file. When users of such "lazy scanner" need to know the next KV precisely (e.g.
* when this scanner is at the top of the heap), they run {@link #enforceSeek()}.
*
* <p>Note that this function does guarantee that the current KV of this scanner will be advanced
* to at least the given KV. Because of this, it does have to do a real seek in cases when the
* seek timestamp is older than the highest timestamp of the file, e.g. when we are trying to seek
* to the next row/column and use OLDEST_TIMESTAMP in the seek key.
*/
@Override
public boolean requestSeek(KeyValue kv, boolean forward, boolean useBloom) throws IOException {
if (kv.getFamilyLength() == 0) {
useBloom = false;
}
boolean haveToSeek = true;
if (useBloom) {
// check ROWCOL Bloom filter first.
if (reader.getBloomFilterType() == StoreFile.BloomType.ROWCOL) {
haveToSeek =
reader.passesGeneralBloomFilter(
kv.getBuffer(),
kv.getRowOffset(),
kv.getRowLength(),
kv.getBuffer(),
kv.getQualifierOffset(),
kv.getQualifierLength());
} else if (this.matcher != null && !matcher.hasNullColumnInQuery() && kv.isDeleteFamily()) {
// if there is no such delete family kv in the store file,
// then no need to seek.
haveToSeek =
reader.passesDeleteFamilyBloomFilter(
kv.getBuffer(), kv.getRowOffset(), kv.getRowLength());
}
}
delayedReseek = forward;
delayedSeekKV = kv;
if (haveToSeek) {
// This row/column might be in this store file (or we did not use the
// Bloom filter), so we still need to seek.
realSeekDone = false;
long maxTimestampInFile = reader.getMaxTimestamp();
long seekTimestamp = kv.getTimestamp();
if (seekTimestamp > maxTimestampInFile) {
// Create a fake key that is not greater than the real next key.
// (Lower timestamps correspond to higher KVs.)
// To understand this better, consider that we are asked to seek to
// a higher timestamp than the max timestamp in this file. We know that
// the next point when we have to consider this file again is when we
// pass the max timestamp of this file (with the same row/column).
cur = kv.createFirstOnRowColTS(maxTimestampInFile);
} else {
// This will be the case e.g. when we need to seek to the next
// row/column, and we don't know exactly what they are, so we set the
// seek key's timestamp to OLDEST_TIMESTAMP to skip the rest of this
// row/column.
enforceSeek();
}
return cur != null;
}
// Multi-column Bloom filter optimization.
// Create a fake key/value, so that this scanner only bubbles up to the top
// of the KeyValueHeap in StoreScanner after we scanned this row/column in
// all other store files. The query matcher will then just skip this fake
// key/value and the store scanner will progress to the next column. This
// is obviously not a "real real" seek, but unlike the fake KV earlier in
// this method, we want this to be propagated to ScanQueryMatcher.
cur = kv.createLastOnRowCol();
realSeekDone = true;
return true;
}
