mapr diffstreamswithcrc

This utility uses a cyclic redundancy check to detect differences between sets of messages in the specified MapR streams. Then, for each set of non-identical messages, it performs a detailed comparison. Finally, it generates one or more directories of sequence files. You can use these files either to make a MapR stream identical to its master or merge the messages from two MapR streams.

Sequence files are binary flat files. You can learn more about them here. To convert a sequence file into a format that you can read, use the MapR Database JSON FormatResult utility.

This utility requires less network bandwidth than the mapr diffstreams utility because it performs a detailed table comparison only on the sets of messages where the CRC algorithm detected a difference. Therefore, consider using this utility when the streams you compare are very similar and you are concerned about the data transfer rate.

This utility considers both the source stream and the destination stream to be a master stream. Therefore, it generates two directories with sequence files. These sequence files contain the puts required to update each stream so that each stream can contain a superset of the messages in both streams at the time at which the utility was run.

These are the directories that the utility generates:
opsForDst
A directory containing sequence files that correspond to each put and delete required to make the destination stream identical to the source stream.
opsForSrc
A directory containing sequence files that correspond to each put and delete required to make the source stream identical to the destination stream.

Requirements

  • When the cluster runs YARN, it must also use zero configuration failover for the ResourceManager.
  • To use this utility, you must have the following permissions:
    • The permission readAce on the volumes where the tables are located.
    • On the source stream: either consumeperm or copyperm.
    • On the destination stream: either consumeperm or copyperm.

    For information about how to set permissions on volumes, see Setting Whole Volume ACEs.

    For information about how to set permissions on streams, see Enabling Table and Stream Authorizations with ACEs.

Note: The mapr user is not treated as a superuser. MapR Event Store For Apache Kafka does not allow the mapr user to run this utility unless that user is given the relevant permission or permissions with access-control expressions.

Run the mapr importstream command to implement the puts and deletes specified in the sequence files.

Syntax

mapr diffstreamswithcrc
-src <srcStream>
-dst <dstStream>
-outdir <output directory>
[-first_exit] Exit when first difference is found

Parameters

Parameter Description
src The path of the first stream to include in the comparison.
dst The path of the second stream to include in the comparison.
outdir The path to a directory in which to place the generated sequence files. The utility creates the specified directory. If the specified directory already exists, the command fails.
first_exit

By default, the utility compares all the data in the specified streams. Use this parameter if you want to exit after the first difference is identified between the streams. The parameter takes no value.