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Linux 2.6 - man page for wrap_log_reader (linux section 3erl)

wrap_log_reader(3erl)		     Erlang Module Definition		    wrap_log_reader(3erl)

       wrap_log_reader - A function to read internally formatted wrap disk logs

       wrap_log_reader	is  a  function  to  read  internally  formatted wrap disk logs, refer to
       disk_log(3erl). wrap_log_reader does not interfere with disk_log activities; there is how-
       ever a known bug in this version of the wrap_log_reader , see chapter bugs below.

       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

       If  a  log  is configured to be distributed, there is a possibility that all items are not
       loggen on all nodes. wrap_log_reader does only read the log on  the  called  node,  it  is
       entirely up to the user to be sure that all items are read.

       chunk(Continuation,  N)	->  {Continuation2,  Terms}  | {Continuation2, Terms, Badbytes} |
       {Continuation2, eof} | {error, Reason}

	      Types  Continuation = continuation()
		     N = int() > 0 | infinity
		     Continuation2 = continuation()
		     Terms= [term()]
		     Badbytes = integer()

	      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.

	      The  first  time chunk is called an initial continuation returned from the open/1 ,
	      open/2 must be provided.

	      When chunk/3 is called, N controls the maximum number of terms that are  read  from
	      the  log	in  each chunk. Default is infinity , which means that all the terms con-
	      tained in the 8K chunk are read. If less than N terms are returned, this	does  not
	      necessarily mean that end of file is reached.

	      The  chunk  function returns a tuple {Continuation2, Terms} , where Terms is a list
	      of terms found in the log. Continuation2 is yet another continuation which must  be
	      passed  on  into any subsequent calls to chunk . With a series of calls to chunk it
	      is then possible to extract all terms from a log.

	      The chunk function returns a tuple {Continuation2, Terms, Badbytes} if the  log  is
	      opened in read only mode and the read chunk is corrupt. Badbytes indicates the num-
	      ber of non-Erlang terms found in the chunk. Note also that the log is not repaired.

	      chunk returns {Continuation2, eof} when the end of the log is reached, and  {error,
	      Reason} if an error occurs.

	      The  returned continuation may or may not be valid in the next call to chunk . 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.

       close(Continuation) -> ok

	      Types  Continuation = continuation()

	      This function closes a log file properly.

       open(Filename) -> OpenRet
       open(Filename, N) -> OpenRet

	      Types  File = string() | atom()
		     N = integer()
		     OpenRet = {ok, Continuation} | {error, Reason}
		     Continuation = continuation()

	      Filename specifies the name of the file which is to be read.

	      N  specifies  the  index of the file which is to be read. If N is omitted the whole
	      wrap log file will be read; if it is specified only the specified index  file  will
	      be read.

	      The open function returns {ok, Continuation} if the log/index file was successfully
	      opened. The Continuation is to be used when chunking or closing the file.

	      The function returns {error, Reason} for all errors.

       This version of the wrap_log_reader does not detect if the disk_log wraps to a  new  index
       file between a wrap_log_reader:open and the first wrap_log_reader:chunk . 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 disk_log .


Ericsson AB				  kernel 2.14.3 		    wrap_log_reader(3erl)

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