com.google.code.externalsorting

Class ExternalSort

java.lang.Object

com.google.code.externalsorting.ExternalSort

public class ExternalSort
extends Object

Goal: offer a generic external-memory sorting program in Java. It must be : - hackable (easy to adapt) - scalable to large files - sensibly efficient. This software is in the public domain. Usage: java com/google/code/externalsorting/ExternalSort somefile.txt out.txt You can change the default maximal number of temporary files with the -t flag: java com/google/code/externalsorting/ExternalSort somefile.txt out.txt -t 3 For very large files, you might want to use an appropriate flag to allocate more memory to the Java VM: java -Xms2G com/google/code/externalsorting/ExternalSort somefile.txt out.txt By (in alphabetical order) Philippe Beaudoin, Eleftherios Chetzakis, Jon Elsas, Christan Grant, Daniel Haran, Daniel Lemire, Sugumaran Harikrishnan, Amit Jain, Thomas Mueller, Jerry Yang, First published: April 2010 originally posted at http://lemire.me/blog/archives/2010/04/01/external-memory-sorting-in-java/

Field Summary

Fields

Modifier and Type	Field and Description
static Comparator<String>	defaultcomparator default comparator between strings.
static int	DEFAULTMAXTEMPFILES Default maximal number of temporary files allowed.

Constructor Summary

Constructors

Constructor and Description
ExternalSort()

Method Summary

Modifier and Type	Method and Description
static long	estimateAvailableMemory() This method calls the garbage collector and then returns the free memory.
static long	estimateBestSizeOfBlocks(long sizeoffile, int maxtmpfiles, long maxMemory) we divide the file into small blocks.
static void	main(String[] args)
static int	mergeSortedFiles(BufferedWriter fbw, Comparator<String> cmp, boolean distinct, List<com.google.code.externalsorting.BinaryFileBuffer> buffers) This merges several BinaryFileBuffer to an output writer.
static int	mergeSortedFiles(List<File> files, File outputfile) This merges a bunch of temporary flat files
static int	mergeSortedFiles(List<File> files, File outputfile, Comparator<String> cmp) This merges a bunch of temporary flat files
static int	mergeSortedFiles(List<File> files, File outputfile, Comparator<String> cmp, boolean distinct) This merges a bunch of temporary flat files
static int	mergeSortedFiles(List<File> files, File outputfile, Comparator<String> cmp, Charset cs) This merges a bunch of temporary flat files
static int	mergeSortedFiles(List<File> files, File outputfile, Comparator<String> cmp, Charset cs, boolean distinct) This merges a bunch of temporary flat files
static int	mergeSortedFiles(List<File> files, File outputfile, Comparator<String> cmp, Charset cs, boolean distinct, boolean append, boolean usegzip) This merges a bunch of temporary flat files
static void	sort(File input, File output) This sorts a file (input) to an output file (output) using default parameters
static File	sortAndSave(List<String> tmplist, Comparator<String> cmp, Charset cs, File tmpdirectory) Sort a list and save it to a temporary file
static File	sortAndSave(List<String> tmplist, Comparator<String> cmp, Charset cs, File tmpdirectory, boolean distinct, boolean usegzip, boolean parallel) Sort a list and save it to a temporary file
static List<File>	sortInBatch(BufferedReader fbr, long datalength) This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.
static List<File>	sortInBatch(BufferedReader fbr, long datalength, Comparator<String> cmp, boolean distinct) This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.
static List<File>	sortInBatch(BufferedReader fbr, long datalength, Comparator<String> cmp, int maxtmpfiles, long maxMemory, Charset cs, File tmpdirectory, boolean distinct, int numHeader, boolean usegzip, boolean parallel) This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.
static List<File>	sortInBatch(File file) This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.
static List<File>	sortInBatch(File file, Comparator<String> cmp) This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.
static List<File>	sortInBatch(File file, Comparator<String> cmp, boolean distinct) This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.
static List<File>	sortInBatch(File file, Comparator<String> cmp, Charset cs, File tmpdirectory, boolean distinct, int numHeader) This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.
static List<File>	sortInBatch(File file, Comparator<String> cmp, File tmpdirectory, boolean distinct, int numHeader) This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.
static List<File>	sortInBatch(File file, Comparator<String> cmp, int maxtmpfiles, Charset cs, File tmpdirectory, boolean distinct) This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.
static List<File>	sortInBatch(File file, Comparator<String> cmp, int maxtmpfiles, Charset cs, File tmpdirectory, boolean distinct, int numHeader) This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.
static List<File>	sortInBatch(File file, Comparator<String> cmp, int maxtmpfiles, Charset cs, File tmpdirectory, boolean distinct, int numHeader, boolean usegzip) This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.
static List<File>	sortInBatch(File file, Comparator<String> cmp, int maxtmpfiles, Charset cs, File tmpdirectory, boolean distinct, int numHeader, boolean usegzip, boolean parallel) This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

defaultcomparator

public static Comparator<String> defaultcomparator

default comparator between strings.

DEFAULTMAXTEMPFILES

public static final int DEFAULTMAXTEMPFILES

Default maximal number of temporary files allowed.

See Also:

Constant Field Values

Constructor Detail

ExternalSort

public ExternalSort()

Method Detail

estimateAvailableMemory

public static long estimateAvailableMemory()

This method calls the garbage collector and then returns the free memory. This avoids problems with applications where the GC hasn't reclaimed memory and reports no available memory.

Returns:

available memory

estimateBestSizeOfBlocks

public static long estimateBestSizeOfBlocks(long sizeoffile,
                                            int maxtmpfiles,
                                            long maxMemory)

we divide the file into small blocks. If the blocks are too small, we shall create too many temporary files. If they are too big, we shall be using too much memory.

Parameters:

sizeoffile - how much data (in bytes) can we expect

maxtmpfiles - how many temporary files can we create (e.g., 1024)

maxMemory - Maximum memory to use (in bytes)

Returns:

the estimate

main

public static void main(String[] args)
                 throws IOException

Parameters:

args - command line argument

Throws:

IOException - generic IO exception

mergeSortedFiles

public static int mergeSortedFiles(BufferedWriter fbw,
                                   Comparator<String> cmp,
                                   boolean distinct,
                                   List<com.google.code.externalsorting.BinaryFileBuffer> buffers)
                            throws IOException

This merges several BinaryFileBuffer to an output writer.

Parameters:

fbw - A buffer where we write the data.

cmp - A comparator object that tells us how to sort the lines.

distinct - Pass true if duplicate lines should be discarded.

buffers - Where the data should be read.

Returns:

The number of lines sorted.

Throws:

IOException - generic IO exception

mergeSortedFiles

public static int mergeSortedFiles(List<File> files,
                                   File outputfile)
                            throws IOException

This merges a bunch of temporary flat files

Parameters:

files - The List of sorted Files to be merged.

outputfile - The output File to merge the results to.

Returns:

The number of lines sorted.

Throws:

IOException - generic IO exception

mergeSortedFiles

public static int mergeSortedFiles(List<File> files,
                                   File outputfile,
                                   Comparator<String> cmp)
                            throws IOException

This merges a bunch of temporary flat files

Parameters:

files - The List of sorted Files to be merged.

outputfile - The output File to merge the results to.

cmp - The Comparator to use to compare Strings.

Returns:

The number of lines sorted.

Throws:

IOException - generic IO exception

mergeSortedFiles

public static int mergeSortedFiles(List<File> files,
                                   File outputfile,
                                   Comparator<String> cmp,
                                   boolean distinct)
                            throws IOException

This merges a bunch of temporary flat files

Parameters:

files - The List of sorted Files to be merged.

outputfile - The output File to merge the results to.

cmp - The Comparator to use to compare Strings.

distinct - Pass true if duplicate lines should be discarded.

Returns:

The number of lines sorted.

Throws:

IOException - generic IO exception

mergeSortedFiles

public static int mergeSortedFiles(List<File> files,
                                   File outputfile,
                                   Comparator<String> cmp,
                                   Charset cs)
                            throws IOException

This merges a bunch of temporary flat files

Parameters:

files - The List of sorted Files to be merged.

outputfile - The output File to merge the results to.

cmp - The Comparator to use to compare Strings.

cs - The Charset to be used for the byte to character conversion.

Returns:

The number of lines sorted.

Throws:

IOException - generic IO exception

mergeSortedFiles

public static int mergeSortedFiles(List<File> files,
                                   File outputfile,
                                   Comparator<String> cmp,
                                   Charset cs,
                                   boolean distinct)
                            throws IOException

This merges a bunch of temporary flat files

Parameters:

files - The List of sorted Files to be merged.

distinct - Pass true if duplicate lines should be discarded.

outputfile - The output File to merge the results to.

cmp - The Comparator to use to compare Strings.

cs - The Charset to be used for the byte to character conversion.

Returns:

The number of lines sorted.

Throws:

IOException - generic IO exception

Since:

v0.1.2

mergeSortedFiles

public static int mergeSortedFiles(List<File> files,
                                   File outputfile,
                                   Comparator<String> cmp,
                                   Charset cs,
                                   boolean distinct,
                                   boolean append,
                                   boolean usegzip)
                            throws IOException

This merges a bunch of temporary flat files

Parameters:

files - The List of sorted Files to be merged.

distinct - Pass true if duplicate lines should be discarded.

outputfile - The output File to merge the results to.

cmp - The Comparator to use to compare Strings.

cs - The Charset to be used for the byte to character conversion.

append - Pass true if result should append to File instead of overwrite. Default to be false for overloading methods.

usegzip - assumes we used gzip compression for temporary files

Returns:

The number of lines sorted.

Throws:

IOException - generic IO exception

Since:

v0.1.4

sort

public static void sort(File input,
                        File output)
                 throws IOException

This sorts a file (input) to an output file (output) using default parameters

Parameters:

input - source file

output - output file

Throws:

IOException - generic IO exception

sortAndSave

public static File sortAndSave(List<String> tmplist,
                               Comparator<String> cmp,
                               Charset cs,
                               File tmpdirectory)
                        throws IOException

Sort a list and save it to a temporary file

Parameters:

tmplist - data to be sorted

cmp - string comparator

cs - charset to use for output (can use Charset.defaultCharset())

tmpdirectory - location of the temporary files (set to null for default location)

Returns:

the file containing the sorted data

Throws:

IOException - generic IO exception

sortAndSave

public static File sortAndSave(List<String> tmplist,
                               Comparator<String> cmp,
                               Charset cs,
                               File tmpdirectory,
                               boolean distinct,
                               boolean usegzip,
                               boolean parallel)
                        throws IOException

Sort a list and save it to a temporary file

Parameters:

tmplist - data to be sorted

cmp - string comparator

cs - charset to use for output (can use Charset.defaultCharset())

tmpdirectory - location of the temporary files (set to null for default location)

distinct - Pass true if duplicate lines should be discarded.

usegzip - set to true if you are using gzip compression for the temporary files

parallel - set to true when sorting in parallel

Returns:

the file containing the sorted data

Throws:

IOException - generic IO exception

sortInBatch

public static List<File> sortInBatch(BufferedReader fbr,
                                     long datalength)
                              throws IOException

This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.

Parameters:

fbr - data source

datalength - estimated data volume (in bytes)

Returns:

a list of temporary flat files

Throws:

IOException - generic IO exception

sortInBatch

public static List<File> sortInBatch(BufferedReader fbr,
                                     long datalength,
                                     Comparator<String> cmp,
                                     boolean distinct)
                              throws IOException

This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.

Parameters:

fbr - data source

datalength - estimated data volume (in bytes)

cmp - string comparator

distinct - Pass true if duplicate lines should be discarded.

Returns:

a list of temporary flat files

Throws:

IOException - generic IO exception

sortInBatch

public static List<File> sortInBatch(BufferedReader fbr,
                                     long datalength,
                                     Comparator<String> cmp,
                                     int maxtmpfiles,
                                     long maxMemory,
                                     Charset cs,
                                     File tmpdirectory,
                                     boolean distinct,
                                     int numHeader,
                                     boolean usegzip,
                                     boolean parallel)
                              throws IOException

This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.

Parameters:

fbr - data source

datalength - estimated data volume (in bytes)

cmp - string comparator

maxtmpfiles - maximal number of temporary files

maxMemory - maximum amount of memory to use (in bytes)

cs - character set to use (can use Charset.defaultCharset())

tmpdirectory - location of the temporary files (set to null for default location)

distinct - Pass true if duplicate lines should be discarded.

numHeader - number of lines to preclude before sorting starts

usegzip - use gzip compression for the temporary files

parallel - sort in parallel

Returns:

a list of temporary flat files

Throws:

IOException - generic IO exception

sortInBatch

public static List<File> sortInBatch(File file)
                              throws IOException

This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.

Parameters:

file - some flat file

Returns:

a list of temporary flat files

Throws:

IOException - generic IO exception

sortInBatch

public static List<File> sortInBatch(File file,
                                     Comparator<String> cmp)
                              throws IOException

This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.

Parameters:

file - some flat file

cmp - string comparator

Returns:

a list of temporary flat files

Throws:

IOException - generic IO exception

sortInBatch

public static List<File> sortInBatch(File file,
                                     Comparator<String> cmp,
                                     boolean distinct)
                              throws IOException

This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later.

Parameters:

file - some flat file

cmp - string comparator

distinct - Pass true if duplicate lines should be discarded.

Returns:

a list of temporary flat files

Throws:

IOException - generic IO exception

sortInBatch

public static List<File> sortInBatch(File file,
                                     Comparator<String> cmp,
                                     File tmpdirectory,
                                     boolean distinct,
                                     int numHeader)
                              throws IOException

This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later. You can specify a bound on the number of temporary files that will be created.

Parameters:

file - some flat file

cmp - string comparator

tmpdirectory - location of the temporary files (set to null for default location)

distinct - Pass true if duplicate lines should be discarded.

numHeader - number of lines to preclude before sorting starts

Returns:

a list of temporary flat files

Throws:

IOException - generic IO exception

sortInBatch

public static List<File> sortInBatch(File file,
                                     Comparator<String> cmp,
                                     int maxtmpfiles,
                                     Charset cs,
                                     File tmpdirectory,
                                     boolean distinct)
                              throws IOException

This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later. You can specify a bound on the number of temporary files that will be created.

Parameters:

file - some flat file

cmp - string comparator

maxtmpfiles - maximal number of temporary files

cs - character set to use (can use Charset.defaultCharset())

tmpdirectory - location of the temporary files (set to null for default location)

distinct - Pass true if duplicate lines should be discarded.

Returns:

a list of temporary flat files

Throws:

IOException - generic IO exception

sortInBatch

public static List<File> sortInBatch(File file,
                                     Comparator<String> cmp,
                                     Charset cs,
                                     File tmpdirectory,
                                     boolean distinct,
                                     int numHeader)
                              throws IOException

This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later. You can specify a bound on the number of temporary files that will be created.

Parameters:

file - some flat file

cmp - string comparator

cs - character set to use (can use Charset.defaultCharset())

tmpdirectory - location of the temporary files (set to null for default location)

distinct - Pass true if duplicate lines should be discarded.

numHeader - number of lines to preclude before sorting starts

Returns:

a list of temporary flat files

Throws:

IOException - generic IO exception

sortInBatch

public static List<File> sortInBatch(File file,
                                     Comparator<String> cmp,
                                     int maxtmpfiles,
                                     Charset cs,
                                     File tmpdirectory,
                                     boolean distinct,
                                     int numHeader)
                              throws IOException

This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later. You can specify a bound on the number of temporary files that will be created.

Parameters:

file - some flat file

cmp - string comparator

maxtmpfiles - maximal number of temporary files

cs - character set to use (can use Charset.defaultCharset())

tmpdirectory - location of the temporary files (set to null for default location)

distinct - Pass true if duplicate lines should be discarded.

numHeader - number of lines to preclude before sorting starts

Returns:

a list of temporary flat files

Throws:

IOException - generic IO exception

sortInBatch

public static List<File> sortInBatch(File file,
                                     Comparator<String> cmp,
                                     int maxtmpfiles,
                                     Charset cs,
                                     File tmpdirectory,
                                     boolean distinct,
                                     int numHeader,
                                     boolean usegzip)
                              throws IOException

This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later. You can specify a bound on the number of temporary files that will be created.

Parameters:

file - some flat file

cmp - string comparator

maxtmpfiles - maximal number of temporary files

cs - character set to use (can use Charset.defaultCharset())

tmpdirectory - location of the temporary files (set to null for default location)

distinct - Pass true if duplicate lines should be discarded.

numHeader - number of lines to preclude before sorting starts

usegzip - use gzip compression for the temporary files

Returns:

a list of temporary flat files

Throws:

IOException - generic IO exception

sortInBatch

public static List<File> sortInBatch(File file,
                                     Comparator<String> cmp,
                                     int maxtmpfiles,
                                     Charset cs,
                                     File tmpdirectory,
                                     boolean distinct,
                                     int numHeader,
                                     boolean usegzip,
                                     boolean parallel)
                              throws IOException

This will simply load the file by blocks of lines, then sort them in-memory, and write the result to temporary files that have to be merged later. You can specify a bound on the number of temporary files that will be created.

Parameters:

file - some flat file

cmp - string comparator

maxtmpfiles - maximal number of temporary files

cs - character set to use (can use Charset.defaultCharset())

tmpdirectory - location of the temporary files (set to null for default location)

distinct - Pass true if duplicate lines should be discarded.

numHeader - number of lines to preclude before sorting starts

usegzip - use gzip compression for the temporary files

parallel - whether to sort in parallel

Returns:

a list of temporary flat files

Throws:

IOException - generic IO exception