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Core: Coalesce nearby blob reads in PuffinReader.readAll #17418

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80 changes: 59 additions & 21 deletions core/src/main/java/org/apache/iceberg/puffin/PuffinReader.java
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Original file line number Diff line number Diff line change
Expand Up @@ -35,13 +35,17 @@
import org.apache.iceberg.puffin.PuffinFormat.Flag;
import org.apache.iceberg.relocated.com.google.common.base.Preconditions;
import org.apache.iceberg.relocated.com.google.common.collect.ImmutableList;
import org.apache.iceberg.relocated.com.google.common.collect.Lists;
import org.apache.iceberg.relocated.com.google.common.io.ByteStreams;
import org.apache.iceberg.util.Pair;

public class PuffinReader implements Closeable {
// Must not be modified
private static final byte[] MAGIC = PuffinFormat.getMagic();

// Bound on a single coalesced read, so a long contiguous run is split into bounded buffers.
private static final long MAX_COALESCED_READ_SIZE = 8 * 1024 * 1024;

private final long fileSize;
private final SeekableInputStream input;
private Integer knownFooterSize;
Expand Down Expand Up @@ -125,27 +129,61 @@ public Iterable<Pair<BlobMetadata, ByteBuffer>> readAll(List<BlobMetadata> blobs
return ImmutableList.of();
}

// TODO inspect blob offsets and coalesce read regions close to each other

return () ->
blobs.stream()
.sorted(Comparator.comparingLong(BlobMetadata::offset))
.map(
(BlobMetadata blobMetadata) -> {
try {
input.seek(blobMetadata.offset());
byte[] bytes = new byte[Math.toIntExact(blobMetadata.length())];
ByteStreams.readFully(input, bytes);
ByteBuffer rawData = ByteBuffer.wrap(bytes);
PuffinCompressionCodec codec =
PuffinCompressionCodec.forName(blobMetadata.compressionCodec());
ByteBuffer data = PuffinFormat.decompress(codec, rawData);
return Pair.of(blobMetadata, data);
} catch (IOException e) {
throw new UncheckedIOException(e);
}
})
.iterator();
List<BlobMetadata> ordered = Lists.newArrayList(blobs);
ordered.sort(Comparator.comparingLong(BlobMetadata::offset));
List<List<BlobMetadata>> groups = coalesce(ordered, MAX_COALESCED_READ_SIZE);

return () -> groups.stream().flatMap(group -> readGroup(group).stream()).iterator();
}

private List<Pair<BlobMetadata, ByteBuffer>> readGroup(List<BlobMetadata> group) {
long start = group.get(0).offset();
long end = start;
for (BlobMetadata blob : group) {
end = Math.max(end, blob.offset() + blob.length());
}

byte[] region;
try {
region = readInput(start, Math.toIntExact(end - start));
} catch (IOException e) {
throw new UncheckedIOException(e);
}

List<Pair<BlobMetadata, ByteBuffer>> data = Lists.newArrayListWithCapacity(group.size());
for (BlobMetadata blob : group) {
int position = Math.toIntExact(blob.offset() - start);
// slice so the blob's bytes align to the buffer's array offset (needed by decompress)
ByteBuffer rawData =
ByteBuffer.wrap(region, position, Math.toIntExact(blob.length())).slice();
PuffinCompressionCodec codec = PuffinCompressionCodec.forName(blob.compressionCodec());
data.add(Pair.of(blob, PuffinFormat.decompress(codec, rawData)));
}

return data;
}

static List<List<BlobMetadata>> coalesce(List<BlobMetadata> orderedByOffset, long maxReadSize) {
List<List<BlobMetadata>> groups = Lists.newArrayList();
List<BlobMetadata> current = null;
long currentStart = 0;
long currentEnd = 0;
for (BlobMetadata blob : orderedByOffset) {
long blobEnd = blob.offset() + blob.length();
boolean gap = current != null && blob.offset() > currentEnd;
boolean tooLarge = current != null && blobEnd - currentStart > maxReadSize;
if (current == null || gap || tooLarge) {
current = Lists.newArrayList();
groups.add(current);
currentStart = blob.offset();
currentEnd = blob.offset();
}

current.add(blob);
currentEnd = Math.max(currentEnd, blobEnd);
}

return groups;
}

private static void checkMagic(byte[] data, int offset) {
Expand Down
75 changes: 75 additions & 0 deletions core/src/test/java/org/apache/iceberg/puffin/TestPuffinReader.java
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Expand Up @@ -28,6 +28,7 @@
import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.assertThatThrownBy;

import java.util.List;
import java.util.Map;
import javax.annotation.Nullable;
import org.apache.iceberg.inmemory.InMemoryInputFile;
Expand Down Expand Up @@ -154,4 +155,78 @@ public void testValidateFooterSizeValue() throws Exception {
.isEqualTo(ImmutableMap.of("created-by", "Test 1234"));
}
}

@Test
void coalescesContiguousBlobsAndSplitsOnGaps() {
BlobMetadata blobA = blob("a", 0, 10);
BlobMetadata blobB = blob("b", 10, 8);
BlobMetadata blobC = blob("c", 15, 10); // overlaps blobB: same read
BlobMetadata blobD = blob("d", 100, 4); // gap: separate read

List<List<BlobMetadata>> groups =
PuffinReader.coalesce(ImmutableList.of(blobA, blobB, blobC, blobD), Long.MAX_VALUE);

assertThat(groups).hasSize(2);
assertThat(groups.get(0)).containsExactly(blobA, blobB, blobC);
assertThat(groups.get(1)).containsExactly(blobD);
}

@Test
void splitsContiguousRunThatExceedsMaxReadSize() {
BlobMetadata blobA = blob("a", 0, 10);
BlobMetadata blobB = blob("b", 10, 10);
BlobMetadata blobC = blob("c", 20, 10); // would exceed the 25-byte cap: separate read

List<List<BlobMetadata>> groups =
PuffinReader.coalesce(ImmutableList.of(blobA, blobB, blobC), 25);

assertThat(groups).hasSize(2);
assertThat(groups.get(0)).containsExactly(blobA, blobB);
assertThat(groups.get(1)).containsExactly(blobC);
}

@Test
void keepsBlobLargerThanMaxReadSizeInItsOwnGroup() {
BlobMetadata big = blob("big", 0, 100); // exceeds the cap on its own
BlobMetadata next = blob("next", 100, 10);

List<List<BlobMetadata>> groups = PuffinReader.coalesce(ImmutableList.of(big, next), 25);

assertThat(groups).hasSize(2);
assertThat(groups.get(0)).containsExactly(big);
assertThat(groups.get(1)).containsExactly(next);
}

@Test
void readAllReadsFarApartBlobsInSeparateRegions() throws Exception {
byte[] first = "first blob".getBytes(UTF_8);
byte[] second = "second blob far away".getBytes(UTF_8);
int secondOffset = 2_000_000; // far from the first blob: separate read

// build the raw layout directly; the writer always packs blobs contiguously
byte[] bytes = new byte[secondOffset + second.length];
System.arraycopy(first, 0, bytes, 0, first.length);
System.arraycopy(second, 0, bytes, secondOffset, second.length);

BlobMetadata firstBlob = blob("first", 0, first.length);
BlobMetadata secondBlob = blob("second", secondOffset, second.length);

InMemoryInputFile inputFile = new InMemoryInputFile(bytes);
try (PuffinReader reader = Puffin.read(inputFile).withFileSize(bytes.length).build()) {
Map<BlobMetadata, byte[]> read =
Streams.stream(reader.readAll(ImmutableList.of(firstBlob, secondBlob)))
.collect(toImmutableMap(Pair::first, pair -> ByteBuffers.toByteArray(pair.second())));

assertThat(read)
.as("read")
.containsOnlyKeys(firstBlob, secondBlob)
.containsEntry(firstBlob, first)
.containsEntry(secondBlob, second);
}
}

private static BlobMetadata blob(String type, long offset, long length) {
return new BlobMetadata(
type, ImmutableList.of(1), 1L, 1L, offset, length, null, ImmutableMap.of());
}
}
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