/**
* @return the key at which the region should be split, or null
* if it cannot be split. This will only be called if shouldSplit
* previously returned true.
*/
protected byte[] getSplitPoint() {
byte[] explicitSplitPoint = this.region.getExplicitSplitPoint();
if (explicitSplitPoint != null) {
return explicitSplitPoint;
}
List<Store> stores = region.getStores();
byte[] splitPointFromLargestStore = null;
long largestStoreSize = 0;
for (Store s : stores) {
byte[] splitPoint = s.getSplitPoint();
long storeSize = s.getSize();
if (splitPoint != null && largestStoreSize < storeSize) {
splitPointFromLargestStore = splitPoint;
largestStoreSize = storeSize;
}
}
return splitPointFromLargestStore;
}
@Override
public byte[] getSplitPoint() {
this.lock.readLock().lock();
try {
// Should already be enforced by the split policy!
assert !this.getRegionInfo().isMetaRegion();
// Not split-able if we find a reference store file present in the store.
if (hasReferences()) {
return null;
}
return this.storeEngine.getStoreFileManager().getSplitPoint();
} catch(IOException e) {
LOG.warn("Failed getting store size for " + this, e);
} finally {
this.lock.readLock().unlock();
}
return null;
}
DefaultStoreFileManager
@Override
public final byte[] getSplitPoint() throws IOException {
if (this.storefiles.isEmpty()) {
return null;
}
return StoreUtils.getLargestFile(this.storefiles).getFileSplitPoint(this.kvComparator);
}
然后到SotreFile的：
/**
* Gets the approximate mid-point of this file that is optimal for use in splitting it.
* @param comparator Comparator used to compare KVs.
* @return The split point row, or null if splitting is not possible, or reader is null.
*/
@SuppressWarnings("deprecation")
byte[] getFileSplitPoint(KVComparator comparator) throws IOException {
if (this.reader == null) {
LOG.warn("Storefile " + this + " Reader is null; cannot get split point");
return null;
}
// Get first, last, and mid keys. Midkey is the key that starts block
// in middle of hfile. Has column and timestamp. Need to return just
// the row we want to split on as midkey.
byte [] midkey = this.reader.midkey();
if (midkey != null) {
KeyValue mk = KeyValue.createKeyValueFromKey(midkey, 0, midkey.length);
byte [] fk = this.reader.getFirstKey();
KeyValue firstKey = KeyValue.createKeyValueFromKey(fk, 0, fk.length);
byte [] lk = this.reader.getLastKey();
KeyValue lastKey = KeyValue.createKeyValueFromKey(lk, 0, lk.length);
// if the midkey is the same as the first or last keys, we cannot (ever) split this region.
if (comparator.compareRows(mk, firstKey) == 0 || comparator.compareRows(mk, lastKey) == 0) {
if (LOG.isDebugEnabled()) {
LOG.debug("cannot split because midkey is the same as first or last row");
}
return null;
}
return mk.getRow();
}
return null;
}