requestTag property

A per-request tag which can be applied to queries or reads, used for statistics collection.

Both request_tag and transaction_tag can be specified for a read or query that belongs to a transaction. This field is ignored for requests where it's not applicable (e.g. CommitRequest). Legal characters for request_tag values are all printable characters (ASCII 32 - 126) and the length of a request_tag is limited to 50 characters. Values that exceed this limit are truncated. Any leading underscore (_) characters will be removed from the string.