package org.apache.lucene.index;
/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.IndexInput;
import org.apache.lucene.store.IndexOutput;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintStream;
import java.util.Vector;
public final class SegmentInfos extends Vector {
/** The file format version, a negative number. */
/* Works since counter, the old 1st entry, is always >= 0 */
public static final int FORMAT = -1;
/** This format adds details used for lockless commits. It differs
* slightly from the previous format in that file names
* are never re-used (write once). Instead, each file is
* written to the next generation. For example,
* segments_1, segments_2, etc. This allows us to not use
* a commit lock. See <a
* href="http://lucene.apache.org/java/docs/fileformats.html">file
* formats</a> for details.
*/
public static final int FORMAT_LOCKLESS = -2;
/** This is the current file format written. It adds a
* "hasSingleNormFile" flag into each segment info.
* See <a href="http://issues.apache.org/jira/browse/LUCENE-756">LUCENE-756</a>
* for details.
*/
public static final int FORMAT_SINGLE_NORM_FILE = -3;
public int counter = 0; // used to name new segments
/**
* counts how often the index has been changed by adding or deleting docs.
* starting with the current time in milliseconds forces to create unique version numbers.
*/
private long version = System.currentTimeMillis();
private long generation = 0; // generation of the "segments_N" for the next commit
private long lastGeneration = 0; // generation of the "segments_N" file we last successfully read
// or wrote; this is normally the same as generation except if
// there was an IOException that had interrupted a commit
/**
* If non-null, information about loading segments_N files
* will be printed here. @see #setInfoStream.
*/
private static PrintStream infoStream;
public final SegmentInfo info(int i) {
return (SegmentInfo) elementAt(i);
}
/**
* Get the generation (N) of the current segments_N file
* from a list of files.
*
* @param files -- array of file names to check
*/
public static long getCurrentSegmentGeneration(String[] files) {
if (files == null) {
return -1;
}
long max = -1;
int prefixLen = IndexFileNames.SEGMENTS.length()+1;
for (int i = 0; i < files.length; i++) {
String file = files[i];
if (file.startsWith(IndexFileNames.SEGMENTS) && !file.equals(IndexFileNames.SEGMENTS_GEN)) {
if (file.equals(IndexFileNames.SEGMENTS)) {
// Pre lock-less commits:
if (max == -1) {
max = 0;
}
} else {
long v = Long.parseLong(file.substring(prefixLen), Character.MAX_RADIX);
if (v > max) {
max = v;
}
}
}
}
return max;
}
/**
* Get the generation (N) of the current segments_N file
* in the directory.
*
* @param directory -- directory to search for the latest segments_N file
*/
public static long getCurrentSegmentGeneration(Directory directory) throws IOException {
String[] files = directory.list();
if (files == null)
throw new IOException("Cannot read directory " + directory);
return getCurrentSegmentGeneration(files);
}
/**
* Get the filename of the current segments_N file
* from a list of files.
*
* @param files -- array of file names to check
*/
public static String getCurrentSegmentFileName(String[] files) throws IOException {
return IndexFileNames.fileNameFromGeneration(IndexFileNames.SEGMENTS,
"",
getCurrentSegmentGeneration(files));
}
/**
* Get the filename of the current segments_N file
* in the directory.
*
* @param directory -- directory to search for the latest segments_N file
*/
public static String getCurrentSegmentFileName(Directory directory) throws IOException {
return IndexFileNames.fileNameFromGeneration(IndexFileNames.SEGMENTS,
"",
getCurrentSegmentGeneration(directory));
}
/**
* Get the segments_N filename in use by this segment infos.
*/
public String getCurrentSegmentFileName() {
return IndexFileNames.fileNameFromGeneration(IndexFileNames.SEGMENTS,
"",
lastGeneration);
}
/**
* Get the next segments_N filename that will be written.
*/
public String getNextSegmentFileName() {
long nextGeneration;
if (generation == -1) {
nextGeneration = 1;
} else {
nextGeneration = generation+1;
}
return IndexFileNames.fileNameFromGeneration(IndexFileNames.SEGMENTS,
"",
nextGeneration);
}
/**
* Read a particular segmentFileName. Note that this may
* throw an IOException if a commit is in process.
*
* @param directory -- directory containing the segments file
* @param segmentFileName -- segment file to load
*/
public final void read(Directory directory, String segmentFileName) throws IOException {
boolean success = false;
IndexInput input = directory.openInput(segmentFileName);
if (segmentFileName.equals(IndexFileNames.SEGMENTS)) {
generation = 0;
} else {
generation = Long.parseLong(segmentFileName.substring(1+IndexFileNames.SEGMENTS.length()),
Character.MAX_RADIX);
}
lastGeneration = generation;
try {
int format = input.readInt();
if(format < 0){ // file contains explicit format info
// check that it is a format we can understand
if (format < FORMAT_SINGLE_NORM_FILE)
throw new IOException("Unknown format version: " + format);
version = input.readLong(); // read version
counter = input.readInt(); // read counter
}
else{ // file is in old format without explicit format info
counter = format;
}
for (int i = input.readInt(); i > 0; i--) { // read segmentInfos
addElement(new SegmentInfo(directory, format, input));
}
if(format >= 0){ // in old format the version number may be at the end of the file
if (input.getFilePointer() >= input.length())
version = System.currentTimeMillis(); // old file format without version number
else
version = input.readLong(); // read version
}
success = true;
}
finally {
input.close();
if (!success) {
// Clear any segment infos we had loaded so we
// have a clean slate on retry:
clear();
}
}
}
/**
* This version of read uses the retry logic (for lock-less
* commits) to find the right segments file to load.
*/
public final void read(Directory directory) throws IOException {
generation = lastGeneration = -1;
new FindSegmentsFile(directory) {
public Object doBody(String segmentFileName) throws IOException {
read(directory, segmentFileName);
return null;
}
}.run();
}
public final void write(Directory directory) throws IOException {
String segmentFileName = getNextSegmentFileName();
// Always advance the generation on write:
if (generation == -1) {
generation = 1;
} else {
generation++;
}
IndexOutput output = directory.createOutput(segmentFileName);
try {
output.writeInt(FORMAT_SINGLE_NORM_FILE); // write FORMAT
output.writeLong(++version); // every write changes
// the index
output.writeInt(counter); // write counter
output.writeInt(size()); // write infos
for (int i = 0; i < size(); i++) {
info(i).write(output);
}
}
finally {
output.close();
}
try {
output = directory.createOutput(IndexFileNames.SEGMENTS_GEN);
try {
output.writeInt(FORMAT_LOCKLESS);
output.writeLong(generation);
output.writeLong(generation);
} finally {
output.close();
}
} catch (IOException e) {
// It's OK if we fail to write this file since it's
// used only as one of the retry fallbacks.
}
lastGeneration = generation;
}
/**
* Returns a copy of this instance, also copying each
* SegmentInfo.
*/
public Object clone() {
SegmentInfos sis = (SegmentInfos) super.clone();
for(int i=0;i<sis.size();i++) {
sis.setElementAt(((SegmentInfo) sis.elementAt(i)).clone(), i);
}
return sis;
}
/**
* version number when this SegmentInfos was generated.
*/
public long getVersion() {
return version;
}
/**
* Current version number from segments file.
*/
public static long readCurrentVersion(Directory directory)
throws IOException {
return ((Long) new FindSegmentsFile(directory) {
public Object doBody(String segmentFileName) throws IOException {
IndexInput input = directory.openInput(segmentFileName);
int format = 0;
long version = 0;
try {
format = input.readInt();
if(format < 0){
if (format < FORMAT_SINGLE_NORM_FILE)
throw new IOException("Unknown format version: " + format);
version = input.readLong(); // read version
}
}
finally {
input.close();
}
if(format < 0)
return new Long(version);
// We cannot be sure about the format of the file.
// Therefore we have to read the whole file and cannot simply seek to the version entry.
SegmentInfos sis = new SegmentInfos();
sis.read(directory, segmentFileName);
return new Long(sis.getVersion());
}
}.run()).longValue();
}
/** If non-null, information about retries when loading
* the segments file will be printed to this.
*/
public static void setInfoStream(PrintStream infoStream) {
SegmentInfos.infoStream = infoStream;
}
/* Advanced configuration of retry logic in loading
segments_N file */
private static int defaultGenFileRetryCount = 10;
private static int defaultGenFileRetryPauseMsec = 50;
private static int defaultGenLookaheadCount = 10;
/**
* Advanced: set how many times to try loading the
* segments.gen file contents to determine current segment
* generation. This file is only referenced when the
* primary method (listing the directory) fails.
*/
public static void setDefaultGenFileRetryCount(int count) {
defaultGenFileRetryCount = count;
}
/**
* @see #setDefaultGenFileRetryCount
*/
public static int getDefaultGenFileRetryCount() {
return defaultGenFileRetryCount;
}
/**
* Advanced: set how many milliseconds to pause in between
* attempts to load the segments.gen file.
*/
public static void setDefaultGenFileRetryPauseMsec(int msec) {
defaultGenFileRetryPauseMsec = msec;
}
/**
* @see #setDefaultGenFileRetryPauseMsec
*/
public static int getDefaultGenFileRetryPauseMsec() {
return defaultGenFileRetryPauseMsec;
}
/**
* Advanced: set how many times to try incrementing the
* gen when loading the segments file. This only runs if
* the primary (listing directory) and secondary (opening
* segments.gen file) methods fail to find the segments
* file.
*/
public static void setDefaultGenLookaheadCount(int count) {
defaultGenLookaheadCount = count;
}
/**
* @see #setDefaultGenLookaheadCount
*/
public static int getDefaultGenLookahedCount() {
return defaultGenLookaheadCount;
}
/**
* @see #setInfoStream
*/
public static PrintStream getInfoStream() {
return infoStream;
}
private static void message(String message) {
if (infoStream != null) {
infoStream.println(Thread.currentThread().getName() + ": " + message);
}
}
/**
* Utility class for executing code that needs to do
* something with the current segments file. This is
* necessary with lock-less commits because from the time
* you locate the current segments file name, until you
* actually open it, read its contents, or check modified
* time, etc., it could have been deleted due to a writer
* commit finishing.
*/
public abstract static class FindSegmentsFile {
File fileDirectory;
Directory directory;
public FindSegmentsFile(File directory) {
this.fileDirectory = directory;
}
public FindSegmentsFile(Directory directory) {
this.directory = directory;
}
public Object run() throws IOException {
String segmentFileName = null;
long lastGen = -1;
long gen = 0;
int genLookaheadCount = 0;
IOException exc = null;
boolean retry = false;
int method = 0;
// Loop until we succeed in calling doBody() without
// hitting an IOException. An IOException most likely
// means a commit was in process and has finished, in
// the time it took us to load the now-old infos files
// (and segments files). It's also possible it's a
// true error (corrupt index). To distinguish these,
// on each retry we must see "forward progress" on
// which generation we are trying to load. If we
// don't, then the original error is real and we throw
// it.
// We have three methods for determining the current
// generation. We try each in sequence.
while(true) {
// Method 1: list the directory and use the highest
// segments_N file. This method works well as long
// as there is no stale caching on the directory
// contents:
String[] files = null;
if (0 == method) {
if (directory != null) {
files = directory.list();
} else {
files = fileDirectory.list();
}
gen = getCurrentSegmentGeneration(files);
if (gen == -1) {
String s = "";
for(int i=0;i<files.length;i++) {
s += " " + files[i];
}
throw new FileNotFoundException("no segments* file found: files:" + s);
}
}
// Method 2 (fallback if Method 1 isn't reliable):
// if the directory listing seems to be stale, then
// try loading the "segments.gen" file.
if (1 == method || (0 == method && lastGen == gen && retry)) {
method = 1;
for(int i=0;i<defaultGenFileRetryCount;i++) {
IndexInput genInput = null;
try {
genInput = directory.openInput(IndexFileNames.SEGMENTS_GEN);
} catch (IOException e) {
message("segments.gen open: IOException " + e);
}
if (genInput != null) {
try {
int version = genInput.readInt();
if (version == FORMAT_LOCKLESS) {
long gen0 = genInput.readLong();
long gen1 = genInput.readLong();
message("fallback check: " + gen0 + "; " + gen1);
if (gen0 == gen1) {
// The file is consistent.
if (gen0 > gen) {
message("fallback to '" + IndexFileNames.SEGMENTS_GEN + "' check: now try generation " + gen0 + " > " + gen);
gen = gen0;
}
break;
}
}
} catch (IOException err2) {
// will retry
} finally {
genInput.close();
}
}
try {
Thread.sleep(defaultGenFileRetryPauseMsec);
} catch (InterruptedException e) {
// will retry
}
}
}
// Method 3 (fallback if Methods 2 & 3 are not
// reliable): since both directory cache and file
// contents cache seem to be stale, just advance the
// generation.
if (2 == method || (1 == method && lastGen == gen && retry)) {
method = 2;
if (genLookaheadCount < defaultGenLookaheadCount) {
gen++;
genLookaheadCount++;
message("look ahead increment gen to " + gen);
}
}
if (lastGen == gen) {
// This means we're about to try the same
// segments_N last tried. This is allowed,
// exactly once, because writer could have been in
// the process of writing segments_N last time.
if (retry) {
// OK, we've tried the same segments_N file
// twice in a row, so this must be a real
// error. We throw the original exception we
// got.
throw exc;
} else {
retry = true;
}
} else {
// Segment file has advanced since our last loop, so
// reset retry:
retry = false;
}
lastGen = gen;
segmentFileName = IndexFileNames.fileNameFromGeneration(IndexFileNames.SEGMENTS,
"",
gen);
try {
Object v = doBody(segmentFileName);
if (exc != null) {
message("success on " + segmentFileName);
}
return v;
} catch (IOException err) {
// Save the original root cause:
if (exc == null) {
exc = err;
}
message("primary Exception on '" + segmentFileName + "': " + err + "'; will retry: retry=" + retry + "; gen = " + gen);
if (!retry && gen > 1) {
// This is our first time trying this segments
// file (because retry is false), and, there is
// possibly a segments_(N-1) (because gen > 1).
// So, check if the segments_(N-1) exists and
// try it if so:
String prevSegmentFileName = IndexFileNames.fileNameFromGeneration(IndexFileNames.SEGMENTS,
"",
gen-1);
if (directory.fileExists(prevSegmentFileName)) {
message("fallback to prior segment file '" + prevSegmentFileName + "'");
try {
Object v = doBody(prevSegmentFileName);
if (exc != null) {
message("success on fallback " + prevSegmentFileName);
}
return v;
} catch (IOException err2) {
message("secondary Exception on '" + prevSegmentFileName + "': " + err2 + "'; will retry");
}
}
}
}
}
}
/**
* Subclass must implement this. The assumption is an
* IOException will be thrown if something goes wrong
* during the processing that could have been caused by
* a writer committing.
*/
protected abstract Object doBody(String segmentFileName) throws IOException;}
}
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