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

NAME

       wrap_log_reader - A function to read internally formatted wrap disk logs

DESCRIPTION

       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 however 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 returned.

       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.

EXPORTS

       chunk(Continuation)
       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 contained 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 possi-
	      ble 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 number 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.

BUGS

       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 .

SEE ALSO

       disk_log(3erl)

Ericsson AB							   kernel 2.14.3					     wrap_log_reader(3erl)