From 68d53c01b0b8e9a007a6a30158c19e34b2d2a34e Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Wed, 18 May 2016 15:53:35 +0200 Subject: Update STDLIB documentation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Language cleaned up by the technical writers xsipewe and tmanevik from Combitech. Proofreading and corrections by Björn Gustavsson and Hans Bolinder. --- lib/stdlib/doc/src/file_sorter.xml | 350 +++++++++++++++++++++---------------- 1 file changed, 195 insertions(+), 155 deletions(-) (limited to 'lib/stdlib/doc/src/file_sorter.xml') diff --git a/lib/stdlib/doc/src/file_sorter.xml b/lib/stdlib/doc/src/file_sorter.xml index bc24f02a99..e988d58c2f 100644 --- a/lib/stdlib/doc/src/file_sorter.xml +++ b/lib/stdlib/doc/src/file_sorter.xml @@ -24,125 +24,150 @@ file_sorter Hans Bolinder - nobody + - nobody - no + + 2001-03-13 PA1 - file_sorter.sgml + file_sorter.xml file_sorter - File Sorter + File sorter. -

The functions of this module sort terms on files, merge already - sorted files, and check files for sortedness. Chunks containing - binary terms are read from a sequence of files, sorted +

This module contains functions for sorting terms on files, merging + already sorted files, and checking files for sortedness. Chunks + containing binary terms are read from a sequence of files, sorted internally in memory and written on temporary files, which are merged producing one sorted file as output. Merging is provided as an optimization; it is faster when the files are already - sorted, but it always works to sort instead of merge. -

+ sorted, but it always works to sort instead of merge.

+

On a file, a term is represented by a header and a binary. Two - options define the format of terms on files: -

- - {header, HeaderLength}. HeaderLength determines the - number of bytes preceding each binary and containing the - length of the binary in bytes. Default is 4. The order of the - header bytes is defined as follows: if B is a binary - containing a header only, the size Size of the binary - is calculated as - > = B]]>. + options define the format of terms on files:

+ + + {header, HeaderLength} + +

HeaderLength determines the + number of bytes preceding each binary and containing the + length of the binary in bytes. Defaults to 4. The order of the + header bytes is defined as follows: if B is a binary + containing a header only, size Size of the binary + is calculated as + > = B]]>.

 - {format, Format}. The format determines the - function that is applied to binaries in order to create the - terms that will be sorted. The default value is - binary_term, which is equivalent to - fun binary_to_term/1. The value binary is - equivalent to fun(X) -> X end, which means that the - binaries will be sorted as they are. This is the fastest - format. If Format is term, io:read/2 is - called to read terms. In that case only the default value of - the header option is allowed. The format option - also determines what is written to the sorted output file: if - Format is term then io:format/3 is called - to write each term, otherwise the binary prefixed by a header - is written. Note that the binary written is the same binary - that was read; the results of applying the Format - function are thrown away as soon as the terms have been - sorted. Reading and writing terms using the io module - is very much slower than reading and writing binaries. + {format, Format} + +

Option Format determines the + function that is applied to binaries to create the + terms to be sorted. Defaults to + binary_term, which is equivalent to + fun binary_to_term/1. Value binary is + equivalent to fun(X) -> X end, which means that the + binaries are sorted as they are. This is the fastest + format. If Format is term, io:read/2 is + called to read terms. In that case, only the default value of + option header is allowed.

+

Option format also determines what is written to the + sorted output file: if + Format is term, then io:format/3 is called + to write each term, otherwise the binary prefixed by a header + is written. Notice that the binary written is the same binary + that was read; the results of applying function Format + are thrown away when the terms have been sorted. + Reading and writing terms using the io module + is much slower than reading and writing binaries.

 - -

Other options are: -

- - {order, Order}. The default is to sort terms in - ascending order, but that can be changed by the value - descending or by giving an ordering function Fun. - An ordering function is antisymmetric, transitive and total. - Fun(A, B) should return true if A - comes before B in the ordering, false otherwise. - An example of a typical ordering function is less than or equal - to, =</2. - Using an ordering function will slow down the sort - considerably. The keysort, keymerge and - keycheck functions do not accept ordering functions. + + +

Other options are:

+ + + {order, Order} + +

The default is to sort terms in + ascending order, but that can be changed by value + descending or by specifying an ordering function Fun. + An ordering function is antisymmetric, transitive, and total. + Fun(A, B) is to return true if A + comes before B in the ordering, otherwise false. + An example of a typical ordering function is less than or equal + to, =</2. Using an ordering function slows down the sort + considerably. Functions keysort, keymerge and + keycheck do not accept ordering functions.

 - {unique, boolean()}. When sorting or merging files, - only the first of a sequence of terms that compare equal (==) - is output if this option is set to true. The default - value is false which implies that all terms that - compare equal are output. When checking files for - sortedness, a check that no pair of consecutive terms - compares equal is done if this option is set to true. + {unique, boolean()} + +

When sorting or merging files, + only the first of a sequence of terms that compare equal (==) + is output if this option is set to true. Defaults + to false, which implies that all terms that + compare equal are output. When checking files for + sortedness, a check that no pair of consecutive terms + compares equal is done if this option is set to true.

 - {tmpdir, TempDirectory}. The directory where - temporary files are put can be chosen explicitly. The - default, implied by the value "", is to put temporary - files on the same directory as the sorted output file. If - output is a function (see below), the directory returned by - file:get_cwd() is used instead. The names of - temporary files are derived from the Erlang nodename - (node()), the process identifier of the current Erlang - emulator (os:getpid()), and a unique integer - (erlang:unique_integer([positive])); a typical name would be - fs_mynode@myhost_1763_4711.17, where - 17 is a sequence number. Existing files will be - overwritten. Temporary files are deleted unless some - uncaught EXIT signal occurs. + {tmpdir, TempDirectory} + +

The directory where + temporary files are put can be chosen explicitly. The + default, implied by value "", is to put temporary + files on the same directory as the sorted output file. If + output is a function (see below), the directory returned by + file:get_cwd() is used instead. The names of + temporary files are derived from the Erlang nodename + (node()), the process identifier of the current Erlang + emulator (os:getpid()), and a unique integer + (erlang:unique_integer([positive])). A typical name is + fs_mynode@myhost_1763_4711.17, where + 17 is a sequence number. Existing files are + overwritten. Temporary files are deleted unless some + uncaught EXIT signal occurs.

 - {compressed, boolean()}. Temporary files and the - output file may be compressed. The default value - false implies that written files are not - compressed. Regardless of the value of the compressed - option, compressed files can always be read. Note that - reading and writing compressed files is significantly slower - than reading and writing uncompressed files. + {compressed, boolean()} + +

Temporary files and the output file can be compressed. Defaults + false, which implies that written files are not + compressed. Regardless of the value of option compressed, + compressed files can always be read. Notice that + reading and writing compressed files are significantly slower + than reading and writing uncompressed files.

 - {size, Size}. By default approximately 512*1024 - bytes read from files are sorted internally. This option - should rarely be needed. + {size, Size} + +

By default about 512*1024 bytes read from files are sorted + internally. This option is rarely needed.

 - {no_files, NoFiles}. By default 16 files are - merged at a time. This option should rarely be needed. + {no_files, NoFiles} + +

By default 16 files are merged at a time. This option is rarely + needed.

 - + +

As an alternative to sorting files, a function of one argument - can be given as input. When called with the argument read - the function is assumed to return end_of_input or - {end_of_input, Value}} when there is no more input - (Value is explained below), or {Objects, Fun}, - where Objects is a list of binaries or terms depending on - the format and Fun is a new input function. Any other - value is immediately returned as value of the current call to - sort or keysort. Each input function will be - called exactly once, and should an error occur, the last - function is called with the argument close, the reply of - which is ignored. -

-

A function of one argument can be given as output. The results + can be specified as input. When called with argument read, + the function is assumed to return either of the following:

+ + + +

end_of_input or {end_of_input, Value}} when there + is no more input (Value is explained below).

+ + +

{Objects, Fun}, where Objects is a list of binaries + or terms depending on the format, and Fun is a new input + function.

+ + + +

Any other value is immediately returned as value of the current call + to sort or keysort. Each input function is + called exactly once. If an error occurs, the last + function is called with argument close, the reply of + which is ignored.

+ +

A function of one argument can be specified as output. The results of sorting or merging the input is collected in a non-empty sequence of variable length lists of binaries or terms depending on the format. The output function is called with one list at a @@ -151,18 +176,20 @@ call to the sort or merge function. Each output function is called exactly once. When some output function has been applied to all of the results or an error occurs, the last function is - called with the argument close, and the reply is returned - as value of the current call to the sort or merge function. If a - function is given as input and the last input function returns - {end_of_input, Value}, the function given as output will - be called with the argument {value, Value}. This makes it + called with argument close, and the reply is returned + as value of the current call to the sort or merge function.

+ +

If a function is specified as input and the last input function + returns {end_of_input, Value}, the function specified as output + is called with argument {value, Value}. This makes it easy to initiate the sequence of output functions with a value - calculated by the input functions. -

+ calculated by the input functions.

+

As an example, consider sorting the terms on a disk log file. A function that reads chunks from the disk log and returns a list of binaries is used as input. The results are collected in a list of terms.

+ 
 sort(Log) ->
     {ok, _} = disk_log:open([{name,Log}, {mode,read_only}]),
@@ -193,29 +220,32 @@ output(L) ->
             lists:append(lists:reverse(L));
        (Terms) ->
             output([Terms | L])
-    end.
-

Further examples of functions as input and output can be found - at the end of the file_sorter module; the term - format is implemented with functions. -

+ end. + +

For more examples of functions as input and output, see + the end of the file_sorter module; the term + format is implemented with functions.

+

The possible values of Reason returned when an error occurs are:

+ -

bad_object, {bad_object, FileName}. +

bad_object, {bad_object, FileName} - Applying the format function failed for some binary, or the key(s) could not be extracted from some term.

 -

{bad_term, FileName}. io:read/2 failed +

{bad_term, FileName} - io:read/2 failed to read some term.

 -

{file_error, FileName, file:posix()}. See - file(3) for an explanation of file:posix().

+

{file_error, FileName, file:posix()} - For an + explanation of file:posix(), see + file(3).

 -

{premature_eof, FileName}. End-of-file was +

{premature_eof, FileName} - End-of-file was encountered inside some binary term.

 @@ -304,30 +334,53 @@ output(L) -> - - Sort terms on files. + + + Check whether terms on files are sorted. -

Sorts terms on files. sort(FileName) is equivalent - to sort([FileName], FileName).

+

Checks files for sortedness. If a file is not sorted, the + first out-of-order element is returned. The first term on a + file has position 1.

+

check(FileName) is equivalent to + check([FileName], []).

 + - - - Sort terms on files. + + + Check whether terms on files are sorted by key. -

Sorts terms on files. sort(Input, Output) is - equivalent to sort(Input, Output, []).

+

Checks files for sortedness. If a file is not sorted, the + first out-of-order element is returned. The first term on a + file has position 1.

+

keycheck(KeyPos, FileName) is equivalent + to keycheck(KeyPos, [FileName], []).

 + + + + + Merge terms on files by key. + +

Merges tuples on files. Each input file is assumed to be + sorted on key(s).

+

keymerge(KeyPos, FileNames, Output) is equivalent + to keymerge(KeyPos, FileNames, Output, []).

+ + + Sort terms on files by key. -

Sorts tuples on files. keysort(N, FileName) is +

Sorts tuples on files.

+

keysort(N, FileName) is equivalent to keysort(N, [FileName], FileName).

 + @@ -335,13 +388,14 @@ output(L) ->

Sorts tuples on files. The sort is performed on the element(s) mentioned in KeyPos. If two - tuples compare equal (==) on one element, next + tuples compare equal (==) on one element, the next element according to KeyPos is compared. The sort is stable.

keysort(N, Input, Output) is equivalent to keysort(N, Input, Output, []).

 + @@ -353,39 +407,25 @@ output(L) -> merge(FileNames, Output, []).

 + - - - Merge terms on files by key. - -

Merges tuples on files. Each input file is assumed to be - sorted on key(s).

-

keymerge(KeyPos, FileNames, Output) is equivalent - to keymerge(KeyPos, FileNames, Output, []).

- - - - - - Check whether terms on files are sorted. + + Sort terms on files. -

Checks files for sortedness. If a file is not sorted, the - first out-of-order element is returned. The first term on a - file has position 1.

-

check(FileName) is equivalent to - check([FileName], []).

+

Sorts terms on files.

+

sort(FileName) is equivalent + to sort([FileName], FileName).

 + - - - Check whether terms on files are sorted by key. + + + Sort terms on files. -

Checks files for sortedness. If a file is not sorted, the - first out-of-order element is returned. The first term on a - file has position 1.

-

keycheck(KeyPos, FileName) is equivalent - to keycheck(KeyPos, [FileName], []).

+

Sorts terms on files.

+

sort(Input, Output) is + equivalent to sort(Input, Output, []).

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