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Diffstat (limited to 'lib/kernel/doc/src/wrap_log_reader.xml')
| -rw-r--r-- | lib/kernel/doc/src/wrap_log_reader.xml | 154 |
1 files changed, 77 insertions, 77 deletions
diff --git a/lib/kernel/doc/src/wrap_log_reader.xml b/lib/kernel/doc/src/wrap_log_reader.xml index c021f42cac..7fb9c1c023 100644 --- a/lib/kernel/doc/src/wrap_log_reader.xml +++ b/lib/kernel/doc/src/wrap_log_reader.xml @@ -4,7 +4,7 @@ <erlref> <header> <copyright> - <year>1998</year><year>2013</year> + <year>1998</year><year>2016</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> @@ -26,39 +26,43 @@ <prepared>Esko Vierumäki</prepared> <responsible>Esko Vierumäki</responsible> <docno></docno> - <approved>nobody</approved> - <checked>no</checked> - <date>98-09-21</date> + <approved></approved> + <checked></checked> + <date>1998-09-21</date> <rev>A</rev> <file>wrap_log_reader.sgml</file> </header> <module>wrap_log_reader</module> - <modulesummary>A function to read internally formatted wrap disk logs</modulesummary> + <modulesummary>A service to read internally formatted wrap disk logs. + </modulesummary> <description> - <p><c>wrap_log_reader</c> is a function to read internally formatted - wrap disk logs, refer to disk_log(3). <c>wrap_log_reader</c> does not - interfere with disk_log activities; there is however a known bug in this - version of the <c>wrap_log_reader</c>, see chapter <c>bugs</c> below. - </p> - <p>A wrap disk log file consists of several files, called index files. - A log file can be opened and closed. It is also possible to open just one index file - separately. If an non-existent or a non-internally formatted file is opened, - an error message is returned. If the file is corrupt, no attempt to repair it - will be done but an error message is returned. - </p> - <p>If a log is configured to be distributed, there is a possibility that all items - are not loggen on all nodes. <c>wrap_log_reader</c> does only read the log on - the called node, it is entirely up to the user to be sure that all items are read. - </p> + <p>This module makes it possible to read internally formatted + wrap disk logs, see + <seealso marker="disk_log"><c>disk_log(3)</c></seealso>. + <c>wrap_log_reader</c> does not + interfere with <c>disk_log</c> activities; there is however a bug in this + version of the <c>wrap_log_reader</c>, see section + <seealso marker="#bugs">Known Limitations</seealso>.</p> + <p>A wrap disk log file consists of many files, called index files. A log + file can be opened and closed. Also, a single index file can be opened + separately. If a non-existent or non-internally formatted file is opened, + an error message is returned. If the file is corrupt, no attempt is made + to repair it, but an error message is returned.</p> + <p>If a log is configured to be distributed, it is possible that all items + are not logged on all nodes. <c>wrap_log_reader</c> only reads the log on + the called node; it is up to the user to be sure that all items + are read.</p> </description> + <datatypes> <datatype> <name name="continuation"/> - <desc><p>Continuation returned by - <c>open/1,2</c> or <c>chunk/1,2</c>.</p> + <desc> + <p>Continuation returned by <c>open/1,2</c> or <c>chunk/1,2</c>.</p> </desc> </datatype> </datatypes> + <funcs> <func> <name name="chunk" arity="1"/> @@ -66,87 +70,83 @@ <fsummary>Read a chunk of objects written to a wrap log.</fsummary> <type name="chunk_ret"/> <desc> - <p>This function makes it possible to efficiently read the - terms which have been appended to a log. It minimises disk - I/O by reading large 8K chunks from the file. - </p> - <p>The first time <c>chunk</c> is called an initial - continuation returned from the <c>open/1</c>, <c>open/2</c> must be provided. - </p> + <p>Enables to efficiently read the + terms that are appended to a log. Minimises disk + I/O by reading 64 kilobyte chunks from the file.</p> + <p>The first time <c>chunk()</c> is called, an initial + continuation returned from <c>open/1</c> or <c>open/2</c> must be + provided.</p> <p>When <c>chunk/3</c> is called, <c><anno>N</anno></c> controls the maximum number of terms that are read from the log in each - chunk. Default is <c>infinity</c>, which means that all the + chunk. Defaults to <c>infinity</c>, which means that all the terms contained in the 8K chunk are read. If less than - <c><anno>N</anno></c> terms are returned, this does not necessarily mean - that end of file is reached. - </p> - <p>The <c>chunk</c> function returns a tuple - <c>{<anno>Continuation2</anno>, <anno>Terms</anno>}</c>, where <c><anno>Terms</anno></c> is a list + <c><anno>N</anno></c> terms are returned, this does not necessarily + mean that end of file is reached.</p> + <p>Returns a tuple <c>{<anno>Continuation2</anno>, + <anno>Terms</anno>}</c>, where <c><anno>Terms</anno></c> is a list of terms found in the log. <c><anno>Continuation2</anno></c> is yet - another continuation which must be passed on into any - subsequent calls to <c>chunk</c>. With a series of calls to - <c>chunk</c> it is then possible to extract all terms from a - log. - </p> - <p>The <c>chunk</c> function returns a tuple - <c>{<anno>Continuation2</anno>, <anno>Terms</anno>, <anno>Badbytes</anno>}</c> if the log is opened - in read only mode and the read chunk is corrupt. <c><anno>Badbytes</anno></c> + another continuation that must be passed on to any + subsequent calls to <c>chunk()</c>. With a series of calls to + <c>chunk()</c>, it is then possible to extract all terms from a log.</p> + <p>Returns a tuple <c>{<anno>Continuation2</anno>, + <anno>Terms</anno>, <anno>Badbytes</anno>}</c> if the log is opened + in read only mode and the read chunk is corrupt. + <c><anno>Badbytes</anno></c> indicates the number of non-Erlang terms found in the chunk. - Note also that the log is not repaired. - </p> - <p><c>chunk</c> returns <c>{<anno>Continuation2</anno>, eof}</c> when the end of the log is - reached, and <c>{error, <anno>Reason</anno>}</c> if an error occurs. - </p> - <p>The returned continuation may or may not be valid in the next call to - <c>chunk</c>. This is because the log may wrap and delete - the file into which the continuation points. To make sure - this does not happen, the log can be blocked during the - search. - </p> + Notice that the log is not repaired.</p> + <p>Returns <c>{<anno>Continuation2</anno>, eof}</c> when + the end of the log is reached, and <c>{error, <anno>Reason</anno>}</c> + if an error occurs.</p> + <p>The returned continuation either is or is not valid in the next call + to this function. This is because the log can wrap and delete + the file into which the continuation points. To ensure + this does not occur, the log can be blocked during the search.</p> </desc> </func> + <func> <name name="close" arity="1"/> - <fsummary>Close a log</fsummary> + <fsummary>Close a log.</fsummary> <desc> - <p>This function closes a log file properly. - </p> + <p>Closes a log file properly.</p> </desc> </func> + <func> <name name="open" arity="1"/> <name name="open" arity="2"/> - <fsummary>Open a log file</fsummary> + <fsummary>Open a log file.</fsummary> <type name="open_ret"/> <desc> - <p><c><anno>Filename</anno></c> specifies the name of the file which is to be read. </p> - <p><c><anno>N</anno></c> specifies the index of the file which is to be read. - If <c><anno>N</anno></c> is omitted the whole wrap log file will be read; if it - is specified only the specified index file will be read. - </p> - <p>The <c>open</c> function returns <c>{ok, <anno>Continuation</anno>}</c> if the - log/index file was successfully opened. The <c><anno>Continuation</anno></c> - is to be used when chunking or closing the file. - </p> - <p>The function returns <c>{error, <anno>Reason</anno>}</c> for all errors. - </p> + <p><c><anno>Filename</anno></c> specifies the name of the file to be + read.</p> + <p><c><anno>N</anno></c> specifies the index of the file to be read. + If <c><anno>N</anno></c> is omitted, the whole wrap log file is read; + if it is specified, only the specified index file is read.</p> + <p>Returns <c>{ok, <anno>Continuation</anno>}</c> if the + log/index file is opened successfully. + <c><anno>Continuation</anno></c> + is to be used when chunking or closing the file.</p> + <p>Returns <c>{error, <anno>Reason</anno>}</c> for all errors.</p> </desc> </func> </funcs> <section> - <title>Bugs</title> - <p>This version of the <c>wrap_log_reader</c> does not detect if the <c>disk_log</c> - wraps to a new index file between a <c>wrap_log_reader:open</c> and the first - <c>wrap_log_reader:chunk</c>. - In this case the chuck will actually read the last logged items in the log file, - because the opened index file was truncated by the <c>disk_log</c>. - </p> + <title>Known Limitations</title> + <marker id="bugs"/> + <p>This version of <c>wrap_log_reader</c> does not detect if + <c>disk_log</c> wraps to a new index file between a call to + <c>wrap_log_reader:open()</c> and the first call to + <c>wrap_log_reader:chunk()</c>. + If this occurs, the call to <c>chunk()</c> reads the last logged + items in the log file, as the opened index file was truncated by + <c>disk_log</c>.</p> </section> <section> <title>See Also</title> - <p><seealso marker="disk_log">disk_log(3)</seealso></p> + <p><seealso marker="disk_log"><c>disk_log(3)</c></seealso></p> </section> </erlref> |