vsop-479 commented on code in PR #13253:
URL: https://github.com/apache/lucene/pull/13253#discussion_r1613089056
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lucene/core/src/java/org/apache/lucene/codecs/lucene90/blocktree/SegmentTermsEnum.java:
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@@ -434,8 +436,29 @@ public boolean seekExact(BytesRef target) throws
IOException {
// System.out.println(" target is before current (shares
prefixLen=" + targetUpto + ");
// rewind frame ord=" + lastFrame.ord);
// }
+
+ // We got lastFrame by comparing target and term, and target less than
last seeked term in
+ // currentFrame. If lastFrame's fp is same with currentFrame's fp, we
can reduce entCount to
+ // nextEnt.
+ boolean currentIsLast = currentFrame.fp == lastFrame.fp;
currentFrame = lastFrame;
- currentFrame.rewind();
+
+ // Only rewindWithoutReload for non-floor block or first floor block.
+ // TODO: We need currentFrame's first entry to judge whether we can
rewindWithoutReload for
+ // non-first floor blocks.
+ if (currentFrame.fp != currentFrame.fpOrig
+ || currentFrame.entCount == 0
+ || currentFrame.nextEnt == -1) {
+ currentFrame.rewind();
+ } else {
+ // Prepare to reduce entCount.
+ if (currentIsLast && currentFrame.isLeafBlock) {
Review Comment:
> One case you can roll back entCount temporarily, because you know the
target term is before the current term?
Yes.
> but you do know the target term is in this current block? But then why are
we even rewinding?
We get `lastFrame` from `stack[0]` firstly, and compare `target` to last
seek'd `term` to update `lastFrame` to reuse seek state, and assign it to
`currentFrame`. This `currentFrame` only got by `target` and last seek'd `term`
's common prefix, we still need to continue walking the index to seek `target`
term's block.
I think we need rewinding to set frame's state (`nextEnt`, `entCount`, etc.)
to prepare for seeking. Unlike `rewind`, `rewindWithoutReload` can keep loaded
block's data (same `FP`).
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