Merge Operator

The Merge operator reduces a stream of events to a single event using a specified merge strategy. It is particularly useful as a subquery for the Transactionize operator. Each field can have a different merge strategy:

• takeDistinct - summarize the field using only distinct values
• takeFirst - summarize the field using the earliest value
• takeLast - summarize the field using the latest value
• join with separator - reduce the field by combining all values into a single string with the specified separator between each value. If no separator is specified a new line is used.

Syntax

• merge

  Merge _raw values and separate them with newlines. Adds a Time field containing the earliest timestamp.

• merge <field>  

  Merge values of the named field and separate them with newlines.

• merge <field> [<strategy>] [as <field>]

  Merge values of the named field using the specified strategy and specify a new name for the field.

• merge <field> [<strategy>] [as <field1>] [,<field> [<strategy>] [as <field2>] ]... 

  Merge a comma-delimited list of fields with separate merge strategies. When no strategy is specified, join with new lines is implied.

Limitation

• The metadata field _messageTime can only use strategies takeFirst and takeLast.

Examples

The following query:

*  | parse "BytesSentPersec = \"*\"" as BytesPersec
| merge BytesPersec join with "--", _messageTime takeLast

produces a result something like this:

A common case for using the merge operator with the Transactionize operator is when all log messages have a common field, such as transaction_id or request_id. Using the merge operator with transactionize merges all the messages with the common fields, for example:

_sourceCategory=travelweb
| parse regex "(?<ip>[0-9]+\.[0-9]+\.[0-9]+\.[0-9]) - "
| transactionize ip (merge ip takeFirst, _raw join with "\n\n\n")

Which provides results like the following. Notice that all the logs from the same IP are now grouped in one record.