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From "Matt Sicker (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LOG4J2-1305) Binary Layout
Date Thu, 03 Mar 2016 17:29:18 GMT

    [ https://issues.apache.org/jira/browse/LOG4J2-1305?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15178184#comment-15178184

Matt Sicker commented on LOG4J2-1305:

Now that sounds interesting.

> Binary Layout
> -------------
>                 Key: LOG4J2-1305
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-1305
>             Project: Log4j 2
>          Issue Type: New Feature
>          Components: Layouts
>            Reporter: Remko Popma
>              Labels: binary
> Logging in a binary format instead of in text can give large performance improvements.

> Logging text means going from a LogEvent object to formatted text, and then converting
this text to bytes. Performance investigations with text-based logging formats like PatternLayout
(see LOG4J2-930), and encoding Strings to bytes (LOG4J2-935, LOG4J2-1151) suggest that formatting
and encoding text is expensive and imposes limits on the performance that can be achieved.

> A different approach would be to convert the LogEvent to a binary representation directly
without creating a text representation first. This would result in extremely compact log files
that are fast to write. The trade-off is that a binary log cannot easily be read in a general-purpose
editor like VI or Notepad. A specialized tool would be necessary to either display or convert
to human-readable form. 
> This ticket proposes a simple BinaryLayout, where each LogEvent is logged in a binary
> *Example BinaryLayout log event record format*
> ||Offset||Type||Log Event Record Field Description||
> |0|long|TimeMillis|
> |8|long|NanoTime|
> |16|int|Level|
> |20|int|Logger name index - string value in separate file|
> |24|int|Thread name index - string value in separate file|
> |28|long|Thread ID|
> |36|int|Thread priority|
> |40|int|Marker index - value & hierarchy in separate file|
> |44|int|ThreadContext key/value pair count|
> |48|int|ThreadContext key1 index - string value in separate file|
> |52|int|ThreadContext value1 index - string value in separate file|
> |56|int|ThreadContext key2 index|
> |60|int|ThreadContext value2 index|
> |64|int|Message length|
> |68|int|Message encoder FQCN index|
> |72|byte[]|Message data - below offset assumes 18 bytes of message data|
> |90|int| Throwable data length|
> |94|byte[]|Throwable data|
> *Repeating String Data*
> Repeating String data like thread names, logger names, marker names and ThreadContextMap
keys and values should be logged only once, after which they can be referenced by their index.
> One way to do this is to save string data to a separate file. The main log file contains
an index (the line number, zero-based) into the string-data file instead of the full string.
Index -1 means the String value was {{null}}. The format of the string-data file can simply
be: each unique string on a separate line (separated by '\n' (0x0A) character). Any '\n' characters
embedded in the string value are Unicode escaped and writen as "\u000A".
> An alternative to separate files is interspersing "string-data" records with "log event"
records. Records could be prefixed with a single byte indicating their record type (e.g. '#'
(0x23)=header, '\n' (0x0A)=log event, '$' (0x24)=string data).
> String-data record format:
> ||Offset||Type||String-Data Record Field Description||
> |0|int|index of the string (each unique String has a unique index)|
> |4|byte[]|the String value, encoded in the standard Java [modified UTF-8|https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html#modified-utf-8]
format used by [DataOutput.writeUTF(String)|https://docs.oracle.com/javase/8/docs/api/java/io/DataOutput.html#writeUTF-java.lang.String-]|
> *Custom Messages*
> Note: custom Messages that implement the {{Encoder}} interface (introduced with LOG4J2-1274)
can be written in binary form directly without first being converted to text (LOG4J2-506).
Any specialized tool for reading binary log files should handle messages of type "text" out
of the box, but could have some plugin mechanism for decoding custom messages.
> A more flexible and less intrusive variation of this is to have a registry of Encoders
that map Classes to the associated Encoder. That would allow not only custom Messages, but
also the content of any ObjectMessage to be encoded in custom binary format. Domain classes
then no longer need to implement the Message interface.
> *Markers*
> TBD: as Matt points out in the comments, Markers are special since they are hierarchic.
One way to deal with this is to manage a separate file to save the Marker hierarchy. Another
way is to do something similar to PatternLayout: treat it as a String value, where the string
includes hierarchy information. I like the simplicity of the latter approach.
> *Versioning*
> The binary file must start with a header, indicating version information and perhaps
schema information providing meta data on the log record. Schema information may make it possible
to include/exclude fields. For version 1.0, the schema can either be fixed like the above
example, or it could be a simple bitmask for the fields mentioned above.
> *Byte Order*
> TBD: Are multi-byte values like ints and longs written in big Endian or little Endian?
This could be specified in the header, or we could fix it to either one. Exchange protocols
like ITCH tend to select a fixed byte order (ITCH uses big Endian - network byte order). I
like the simplicity of this approach.

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