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Paged - s/RandomAccessFile/MappedByteBuffer/g
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This is a VERY quick hack to test whether we get performance by mapping paged files instead of using an RAF; we do, so it stays for now, but there are a lot of questions. Does write() even work correctly yet ?

An alternative may be to use the org.apache.pdfbox.io.RandomAccessFile as a drop in replacement offering potential performance gain.

But yes, goes from about 7.7s to about 7.2s, and profiles agree that the big CPU hogs have disappeared.
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@alanpaxton @adamretter
alanpaxton authored and adamretter committed Nov 9, 2023
1 parent f83a693 commit 5e5d062
Showing 1 changed file with 79 additions and 32 deletions.
111 changes: 79 additions & 32 deletions exist-core/src/main/java/org/exist/storage/btree/Paged.java
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Original file line number Diff line number Diff line change
Expand Up @@ -80,17 +80,23 @@
import org.exist.util.FileUtils;
import org.exist.xquery.Constants;

import java.lang.AutoCloseable;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintStream;
import java.io.RandomAccessFile;
import java.io.UncheckedIOException;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.channels.NonWritableChannelException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

/**
* Paged is a paged file foundation that is used by the BTree class and
Expand Down Expand Up @@ -134,7 +140,7 @@ public abstract class Paged implements AutoCloseable {
private final byte[] tempPageData;
private final byte[] tempHeaderData;

private RandomAccessFile raf;
private MappedByteBuffer mapped;
private Path file;
private boolean readOnly = false;
private boolean fileIsNew = false;
Expand Down Expand Up @@ -166,13 +172,27 @@ public final boolean isReadOnly() {
@Override
public void close() throws DBException {
try {
raf.close();
} catch (final IOException e) {
mapped.force();
final MappedByteBuffer mappedBuffer = mapped;
mapped = null;
closeMapped(mappedBuffer);
} catch (final ReflectiveOperationException e) {
throw new DBException("An error occurred whilst closing a mapped file buffer': " + e.getMessage());
} catch (final UncheckedIOException e) {
throw new DBException("An error occurred whilst closing the database file '"
+ file == null ? "null" : FileUtils.fileName(file) + "': " + e.getMessage());
+ (file == null ? "null" : FileUtils.fileName(file) + "': " + e.getMessage()));
}
}

private void closeMapped(MappedByteBuffer mappedBuffer) throws ReflectiveOperationException {
Class<?> unsafeClass = Class.forName("sun.misc.Unsafe");
Field unsafeField = unsafeClass.getDeclaredField("theUnsafe");
unsafeField.setAccessible(true);
Object unsafe = unsafeField.get(null);
Method invokeCleaner = unsafeClass.getMethod("invokeCleaner", ByteBuffer.class);
invokeCleaner.invoke(unsafe, mappedBuffer);
}

/**
* Completely close down the instance and
* all underlying resources and caches.
Expand Down Expand Up @@ -242,11 +262,16 @@ public boolean flush() throws DBException {
* @throws IOException if an I/O error occurs
*/
public void backupToStream(final OutputStream os) throws IOException {
raf.seek(0);
final byte[] buf = new byte[4096];
int len;
while ((len = raf.read(buf)) > 0) {
final int limit = mapped.capacity();
final int block = 4096;
final byte[] buf = new byte[block];
int copied = 0;
mapped.position(0);
while (copied < limit) {
final int len = Math.min(limit - copied, block);
mapped.get(buf, 0, len);
os.write(buf, 0, len);
copied += len;
}
}

Expand Down Expand Up @@ -393,29 +418,51 @@ public void printFreeSpaceList(final PrintStream out) throws IOException {
* @param file The File
*
* @throws DBException if a database error occurs
*
* TODO (AP) - we need to perform multiple mappings for very large files
*/
protected final void setFile(final Path file) throws DBException {
this.file = file;
fileIsNew = !Files.exists(file);
try {
if ((!Files.exists(file)) || Files.isWritable(file)) {
try {
raf = new RandomAccessFile(file.toFile(), "rw");
final FileChannel channel = raf.getChannel();
final FileLock lock = channel.tryLock();
if (lock == null) {
readOnly = true;
final Set<StandardOpenOption> options = new HashSet<StandardOpenOption>();
options.add(StandardOpenOption.CREATE);
options.add(StandardOpenOption.WRITE);
options.add(StandardOpenOption.READ);
try (FileChannel fc = FileChannel.open(file, options)) {
if (fc.size() > Integer.MAX_VALUE) {
throw new DBException("TODO (AP) file too big for temporary hack: " + file);
}
final FileLock lock = fc.tryLock();
if (lock == null) {
mapped = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
readOnly = true;
} else {
mapped = fc.map(FileChannel.MapMode.READ_WRITE, 0, fc.size());
}
}
//TODO : who will release the lock ? -pb
//TODO : who will release the lock ? -pb
} catch (final NonWritableChannelException e) {
//No way : switch to read-only mode
readOnly = true;
raf = new RandomAccessFile(file.toFile(), "r");
try (FileChannel fc = FileChannel.open(file, StandardOpenOption.READ)) {
if (fc.size() > Integer.MAX_VALUE) {
throw new DBException("FIXME file too big for temporary hack: " + file);
}
mapped = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
}
LOG.warn(e);
}
} else {
readOnly = true;
raf = new RandomAccessFile(file.toFile(), "r");
try (FileChannel fc = FileChannel.open(file, StandardOpenOption.READ)) {
if (fc.size() > Integer.MAX_VALUE) {
throw new DBException("FIXME file too big for temporary hack: " + file);
}
mapped = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
}
}
} catch (final IOException e) {
LOG.warn("An exception occurred while opening database file {}: {}", file.toAbsolutePath().toString(), e.getMessage(), e);
Expand Down Expand Up @@ -711,8 +758,8 @@ public final boolean isDirty() {
}

public final synchronized void read() throws IOException {
raf.seek(0);
raf.read(buf);
mapped.position(0);
mapped.get(buf);
read(buf);
calculateWorkSize();
dirty = false;
Expand Down Expand Up @@ -848,9 +895,9 @@ public final void setTotalCount(final long totalCount) {
}

public final synchronized void write() throws IOException {
raf.seek(0);
mapped.position(0);
write(buf);
raf.write(buf);
mapped.put(buf);
dirty = false;
}
}
Expand Down Expand Up @@ -944,16 +991,16 @@ public void incRefCount() {

public byte[] read() throws IOException {
try {
if (raf.getFilePointer() != offset) {
raf.seek(offset);
if (mapped.position() != offset) {
mapped.position((int)offset);
}
Arrays.fill(tempHeaderData, (byte)0);
raf.read(tempHeaderData);
mapped.get(tempHeaderData);
// Read in the header
header.read(tempHeaderData, 0);
// Read the working data
final byte[] workData = new byte[header.dataLen];
raf.read(workData);
mapped.get(workData);
return workData;
} catch(final Exception e) {
LOG.warn("error while reading page: {}", getPageInfo(), e);
Expand Down Expand Up @@ -986,10 +1033,10 @@ private final void write(final byte[] data) throws IOException {
System.arraycopy(data, 0, tempPageData, fileHeader.pageHeaderSize, data.length);
}
}
if (raf.getFilePointer() != offset) {
raf.seek(offset);
if (mapped.position() != offset) {
mapped.position((int)offset);
}
raf.write(tempPageData);
mapped.put(tempPageData);
}

@Override
Expand All @@ -1009,11 +1056,11 @@ public int compareTo(final Page other) {
}

public void dumpPage() throws IOException {
if (raf.getFilePointer() != offset) {
raf.seek(offset);
if (mapped.position() != offset) {
mapped.position((int)offset);
}
final byte[] data = new byte[fileHeader.pageSize];
raf.read(data);
mapped.get(data);
LOG.debug("Contents of page {}: {}", pageNum, hexDump(data));
}
}
Expand Down

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