mikemccand commented on code in PR #12653:
URL: https://github.com/apache/lucene/pull/12653#discussion_r1364204027
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lucene/core/src/java/org/apache/lucene/codecs/MultiLevelSkipListWriter.java:
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@@ -63,24 +63,23 @@ public abstract class MultiLevelSkipListWriter {
/** for every skip level a different buffer is used */
private ByteBuffersDataOutput[] skipBuffer;
+ /** Length of the window at which the skips are placed on skip level 1 */
+ private final long windowLength;
+
/** Creates a {@code MultiLevelSkipListWriter}. */
protected MultiLevelSkipListWriter(
int skipInterval, int skipMultiplier, int maxSkipLevels, int df) {
this.skipInterval = skipInterval;
this.skipMultiplier = skipMultiplier;
- int numberOfSkipLevels;
+ int numberOfSkipLevels = 1;
// calculate the maximum number of skip levels for this document frequency
- if (df <= skipInterval) {
- numberOfSkipLevels = 1;
- } else {
- numberOfSkipLevels = 1 + MathUtil.log(df / skipInterval, skipMultiplier);
- }
-
- // make sure it does not exceed maxSkipLevels
- if (numberOfSkipLevels > maxSkipLevels) {
- numberOfSkipLevels = maxSkipLevels;
+ if (df > skipInterval) {
+ // also make sure it does not exceed maxSkipLevels
+ numberOfSkipLevels =
+ Math.min(1 + MathUtil.log(df / skipInterval, skipMultiplier),
maxSkipLevels);
}
Review Comment:
Could we move the `numberOfSkiLevels = 1` onto an `else` clause here?
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lucene/core/src/java/org/apache/lucene/codecs/MultiLevelSkipListWriter.java:
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@@ -130,12 +129,14 @@ public void bufferSkip(int df) throws IOException {
assert df % skipInterval == 0;
int numLevels = 1;
- df /= skipInterval;
-
- // determine max level
- while ((df % skipMultiplier) == 0 && numLevels < numberOfSkipLevels) {
+ if (df % windowLength == 0) {
Review Comment:
So this optimizes for the common case when `numLevels` will be `1`, right?
It does a single modulo check to catch that case, and only if `numLevels` will
be > 1 does it fall into the `while` loop case.
Maybe add some comments explaining this? Perhaps even the beautiful ascii
art you put in the opening description?
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