Description:
Java client library is adding support for tagging googleapis/java-spanner#576
Similarly python client can also add support to enable users to set tags on database operations such as reads, queries and transactions.

Background
The statistics of queries, reads and transactions in Cloud Spanner are stored. Providing tags for database operations will allow these statistics to be grouped by a tag and makes queries/transactions easily searchable by tag. This will help make the information provided by the statistics more useful.