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SQLMetric

Spark Plan 包含以下基本 方法，

  /*** @return All metrics containing metrics of this SparkPlan.*/def metrics: Map[String, SQLMetric] = Map.empty

  /*** @return [[SQLMetric]] for the `name`.*/def longMetric(name: String): SQLMetric = metrics(name)

BytesToBytesMap

public final class BytesToBytesMap extends MemoryConsumer {

  /*** Returns the average number of probes per key lookup.*/public double getAvgHashProbesPerKey() {return (1.0 * numProbes) / numKeyLookups;}

  /*** Looks up a key, and saves the result in provided `loc`.** This is a thread-safe version of `lookup`, could be used by multiple threads.*/public void safeLookup(Object keyBase, long keyOffset, int keyLength, Location loc, int hash) {assert(longArray != null);numKeyLookups++;int pos = hash & mask;int step = 1;while (true) {numProbes++;if (longArray.get(pos * 2) == 0) {// This is a new key.loc.with(pos, hash, false);return;} else {long stored = longArray.get(pos * 2 + 1);if ((int) (stored) == hash) {// Full hash code matches.  Let's compare the keys for equality.loc.with(pos, hash, true);if (loc.getKeyLength() == keyLength) {final boolean areEqual = ByteArrayMethods.arrayEquals(keyBase,keyOffset,loc.getKeyBase(),loc.getKeyOffset(),keyLength);if (areEqual) {return;}}}}pos = (pos + step) & mask;step++;}}

这里， hashprobe 本质上就是一个 hash lookup 的过程