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Use IndexInput#prefetch for postings, skip data and impacts (#13364) 

This uses the `IndexInput#prefetch` API for postings. This relies on heuristics, as we don't know ahead of time what data we will need from a postings list:
 - Postings lists are prefetched entirely when they are short (< 16kB).
 - Impacts enums also prefetch the first page of skip data.
 - Postings enums prefetc skip data on the first call to advance().

Positions, offsets and payloads are never prefetched.

Putting the `IndexInput#prefetch` call in `TermsEnum#postings` and `TermsEnum#impacts` works well because `BooleanQuery` will first create postings/impacts enums for all clauses before it starts unioning/intersecting them. This allows the prefetching logic to run in parallel across all clauses of the same query on the same segment.
This commit is contained in:
Adrien Grand 2024-05-17 09:07:07 +02:00 committed by GitHub
parent 3d671a0fbe
commit c5331df1c4
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1 changed files with 102 additions and 41 deletions
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75
lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99PostingsReader.java
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@ -53,6 +53,9 @@ import org.apache.lucene.util.IOUtils;
*/
public final class Lucene99PostingsReader extends PostingsReaderBase {
/** Maximum byte size of a postings list to be fully prefetched. */
private static final int MAX_POSTINGS_SIZE_FOR_FULL_PREFETCH = 16_384;
private final IndexInput docIn;
private final IndexInput posIn;
private final IndexInput payIn;
@ -321,6 +324,7 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
private Lucene99SkipReader skipper;
private boolean skipped;
private boolean prefetchedSkipData;
final IndexInput startDocIn;
@ -393,7 +397,7 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
// lazy init
docIn = startDocIn.clone();
}
docIn.seek(docTermStartFP);
seekAndPrefetchPostings(docIn, termState);
}
doc = -1;
@ -409,6 +413,7 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
nextSkipDoc = BLOCK_SIZE - 1; // we won't skip if target is found in first block
docBufferUpto = BLOCK_SIZE;
skipped = false;
prefetchedSkipData = false;
return this;
}
@ -501,8 +506,15 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
public int advance(int target) throws IOException {
// current skip docID < docIDs generated from current buffer <= next skip docID
// we don't need to skip if target is buffered already
if (docFreq > BLOCK_SIZE && target > nextSkipDoc) {
if (docFreq > BLOCK_SIZE) {
if (target <= nextSkipDoc) {
// We don't need skip data yet, but we have evidence that advance() is called, so let's
// prefetch skip data in the background.
if (prefetchedSkipData == false) {
prefetchSkipData(docIn, docTermStartFP, skipOffset);
prefetchedSkipData = true;
}
} else {
if (skipper == null) {
// Lazy init: first time this enum has ever been used for skipping
skipper =
@ -540,6 +552,7 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
// foresee whether skipper is necessary.
nextSkipDoc = skipper.getNextSkipDoc();
}
}
if (docBufferUpto == BLOCK_SIZE) {
refillDocs();
}
@ -594,6 +607,7 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
private Lucene99SkipReader skipper;
private boolean skipped;
private boolean prefetchedSkipData;
final IndexInput startDocIn;
@ -715,7 +729,7 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
// lazy init
docIn = startDocIn.clone();
}
docIn.seek(docTermStartFP);
seekAndPrefetchPostings(docIn, termState);
}
posPendingFP = posTermStartFP;
payPendingFP = payTermStartFP;
@ -741,6 +755,7 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
}
docBufferUpto = BLOCK_SIZE;
skipped = false;
prefetchedSkipData = false;
return this;
}
@ -902,6 +917,13 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
payloadByteUpto = skipper.getPayloadByteUpto();
}
nextSkipDoc = skipper.getNextSkipDoc();
} else {
// We don't need skip data yet, but we have evidence that advance() is used, so prefetch it
// in the background.
if (prefetchedSkipData == false) {
prefetchSkipData(docIn, docTermStartFP, skipOffset);
prefetchedSkipData = true;
}
}
if (docBufferUpto == BLOCK_SIZE) {
refillDocs();
@ -1097,7 +1119,9 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
this.docIn = Lucene99PostingsReader.this.docIn.clone();
docFreq = termState.docFreq;
docIn.seek(termState.docStartFP);
seekAndPrefetchPostings(docIn, termState);
// Impacts almost certainly need skip data
prefetchSkipData(docIn, termState.docStartFP, termState.skipOffset);
doc = -1;
accum = 0;
@ -1318,7 +1342,8 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
posTermStartFP = termState.posStartFP;
payTermStartFP = termState.payStartFP;
totalTermFreq = termState.totalTermFreq;
docIn.seek(docTermStartFP);
seekAndPrefetchPostings(docIn, termState);
prefetchSkipData(docIn, termState.docStartFP, termState.skipOffset);
posPendingFP = posTermStartFP;
posPendingCount = 0;
if (termState.totalTermFreq < BLOCK_SIZE) {
@ -1672,7 +1697,8 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
posTermStartFP = termState.posStartFP;
payTermStartFP = termState.payStartFP;
totalTermFreq = termState.totalTermFreq;
docIn.seek(docTermStartFP);
seekAndPrefetchPostings(docIn, termState);
prefetchSkipData(docIn, termState.docStartFP, termState.skipOffset);
posPendingFP = posTermStartFP;
payPendingFP = payTermStartFP;
posPendingCount = 0;
@ -2049,6 +2075,41 @@ public final class Lucene99PostingsReader extends PostingsReaderBase {
}
}
private void seekAndPrefetchPostings(IndexInput docIn, IntBlockTermState state)
throws IOException {
if (docIn.getFilePointer() != state.docStartFP) {
// Don't prefetch if the input is already positioned at the right offset, which suggests that
// the caller is streaming the entire inverted index (e.g. for merging), let the read-ahead
// logic do its work instead. Note that this heuristic doesn't work for terms that have skip
// data, since skip data is stored after the last term, but handling all terms that have <128
// docs is a good start already.
docIn.seek(state.docStartFP);
if (state.skipOffset < 0) {
// This postings list is very short as it doesn't have skip data, prefetch the page that
// holds the first byte of the postings list.
docIn.prefetch(state.docStartFP, 1);
} else if (state.skipOffset <= MAX_POSTINGS_SIZE_FOR_FULL_PREFETCH) {
// This postings list is short as it fits on a few pages, prefetch it all, plus one byte to
// make sure to include some skip data.
docIn.prefetch(state.docStartFP, state.skipOffset + 1);
} else {
// Default case: prefetch the page that holds the first byte of postings. We'll prefetch
// skip data when we have evidence that it is used.
docIn.prefetch(state.docStartFP, 1);
}
}
// Note: we don't prefetch positions or offsets, which are less likely to be needed.
}
private void prefetchSkipData(IndexInput docIn, long docStartFP, long skipOffset)
throws IOException {
if (skipOffset > MAX_POSTINGS_SIZE_FOR_FULL_PREFETCH) {
// If skipOffset is less than this value, skip data was already prefetched when doing
// #seekAndPrefetchPostings
docIn.prefetch(docStartFP + skipOffset, 1);
}
}
@Override
public void checkIntegrity() throws IOException {
if (docIn != null) {