jsedding commented on code in PR #2513:
URL: https://github.com/apache/jackrabbit-oak/pull/2513#discussion_r2359952723
##########
oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/spi/persistence/persistentcache/CachingSegmentArchiveReader.java:
##########
@@ -19,34 +19,123 @@
package org.apache.jackrabbit.oak.segment.spi.persistence.persistentcache;
import org.apache.jackrabbit.oak.commons.Buffer;
+import org.apache.jackrabbit.oak.commons.concurrent.ExecutorCloser;
+import org.apache.jackrabbit.oak.segment.data.SegmentData;
import org.apache.jackrabbit.oak.segment.file.tar.SegmentGraph;
import org.apache.jackrabbit.oak.segment.spi.persistence.SegmentArchiveEntry;
import org.apache.jackrabbit.oak.segment.spi.persistence.SegmentArchiveReader;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
import java.util.List;
+import java.util.Set;
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
public class CachingSegmentArchiveReader implements SegmentArchiveReader {
+ private static final Logger LOG =
LoggerFactory.getLogger(CachingSegmentArchiveReader.class);
+
+
@NotNull
private final PersistentCache persistentCache;
@NotNull
private final SegmentArchiveReader delegate;
+ private final ExecutorService prefetchExecutor;
+ private final Set<UUID> inFlightPrefetch =
+ Collections.newSetFromMap(
+ new ConcurrentHashMap<>());
+ private final boolean prefetchEnabled;
+ private final int prefetchMaxRefs;
+
+
+
public CachingSegmentArchiveReader(
@NotNull PersistentCache persistentCache,
@NotNull SegmentArchiveReader delegate) {
this.persistentCache = persistentCache;
this.delegate = delegate;
+ int threads = Integer.getInteger("oak.segment.cache.threads", 10);
+ this.prefetchEnabled =
Boolean.getBoolean("oak.segment.cache.prefetch.enabled");
+ this.prefetchMaxRefs =
Integer.getInteger("oak.segment.cache.prefetch.maxRefs", 20);
+ this.prefetchExecutor = Executors.newFixedThreadPool(threads);
}
@Override
@Nullable
public Buffer readSegment(long msb, long lsb) throws IOException {
- return persistentCache.readSegment(msb, lsb, () ->
delegate.readSegment(msb, lsb));
+ Buffer buf = persistentCache.readSegment(msb, lsb, () ->
delegate.readSegment(msb, lsb));
+ if (buf != null && prefetchEnabled) {
+ schedulePrefetch(msb, lsb, buf);
+ }
+ return buf;
+ }
+
+ private List<UUID> extractReferences(Buffer buffer) {
+ var data = SegmentData.newSegmentData(buffer);
+ int refs = data.getSegmentReferencesCount();
+ ArrayList<UUID> out = new ArrayList<>(refs);
+ for (int i = 0; i < refs; i++) {
+ out.add(new UUID(data.getSegmentReferenceMsb(i),
data.getSegmentReferenceLsb(i)));
+ }
+ return out;
+ }
+
+ private void schedulePrefetch(long msb, long lsb, Buffer buffer) {
+ try {
+ List<UUID> refs = extractReferences(buffer);
+ int limit = Math.min(refs.size(), prefetchMaxRefs);
+ for (int i = 0; i < limit; i++) {
+ final UUID ref = refs.get(i);
+ final long rMsb = ref.getMostSignificantBits();
+ final long rLsb = ref.getLeastSignificantBits();
+
+ // Skip if already present in cache
+ if (persistentCache.containsSegment(rMsb, rLsb)) {
+ continue;
+ }
+
+ // Drop prefetch if already in progress for this segment
+ boolean registered = inFlightPrefetch.add(ref);
Review Comment:
Nice idea! I missed this trick so far in #2519 🙂
##########
oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/spi/persistence/persistentcache/CachingSegmentArchiveReader.java:
##########
@@ -19,34 +19,123 @@
package org.apache.jackrabbit.oak.segment.spi.persistence.persistentcache;
import org.apache.jackrabbit.oak.commons.Buffer;
+import org.apache.jackrabbit.oak.commons.concurrent.ExecutorCloser;
+import org.apache.jackrabbit.oak.segment.data.SegmentData;
import org.apache.jackrabbit.oak.segment.file.tar.SegmentGraph;
import org.apache.jackrabbit.oak.segment.spi.persistence.SegmentArchiveEntry;
import org.apache.jackrabbit.oak.segment.spi.persistence.SegmentArchiveReader;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
import java.util.List;
+import java.util.Set;
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
public class CachingSegmentArchiveReader implements SegmentArchiveReader {
+ private static final Logger LOG =
LoggerFactory.getLogger(CachingSegmentArchiveReader.class);
+
+
@NotNull
private final PersistentCache persistentCache;
@NotNull
private final SegmentArchiveReader delegate;
+ private final ExecutorService prefetchExecutor;
+ private final Set<UUID> inFlightPrefetch =
+ Collections.newSetFromMap(
+ new ConcurrentHashMap<>());
+ private final boolean prefetchEnabled;
+ private final int prefetchMaxRefs;
+
+
+
public CachingSegmentArchiveReader(
@NotNull PersistentCache persistentCache,
@NotNull SegmentArchiveReader delegate) {
this.persistentCache = persistentCache;
this.delegate = delegate;
+ int threads = Integer.getInteger("oak.segment.cache.threads", 10);
+ this.prefetchEnabled =
Boolean.getBoolean("oak.segment.cache.prefetch.enabled");
+ this.prefetchMaxRefs =
Integer.getInteger("oak.segment.cache.prefetch.maxRefs", 20);
+ this.prefetchExecutor = Executors.newFixedThreadPool(threads);
}
@Override
@Nullable
public Buffer readSegment(long msb, long lsb) throws IOException {
- return persistentCache.readSegment(msb, lsb, () ->
delegate.readSegment(msb, lsb));
+ Buffer buf = persistentCache.readSegment(msb, lsb, () ->
delegate.readSegment(msb, lsb));
+ if (buf != null && prefetchEnabled) {
+ schedulePrefetch(msb, lsb, buf);
+ }
+ return buf;
+ }
+
+ private List<UUID> extractReferences(Buffer buffer) {
+ var data = SegmentData.newSegmentData(buffer);
+ int refs = data.getSegmentReferencesCount();
+ ArrayList<UUID> out = new ArrayList<>(refs);
+ for (int i = 0; i < refs; i++) {
+ out.add(new UUID(data.getSegmentReferenceMsb(i),
data.getSegmentReferenceLsb(i)));
+ }
+ return out;
+ }
+
+ private void schedulePrefetch(long msb, long lsb, Buffer buffer) {
Review Comment:
Indeed, my tests with #2519, which implements a similar mechanism, but on a
different level of abstraction, showed that dispatching from the caller thread
hurts performance.
I even opted to trigger preloading only from within the load-callback, so
preloading is completely off the critical path for cache hits.
Of course that's a trade-off, as it requires the caller thread to load one
segment before any preloading happens.
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