How can I perform a full table scan without the row limit per query? #

Vitess supports different modes. In OLTP mode, the result size is typically limited to a preset number (10,000 rows by default). This limit can be adjusted based on your needs.

However, OLAP mode has no limit to the number of rows returned. In order to change to this mode, you may issue the following command before executing your query:

set workload='olap'

You can also set the workload to dba, which allows you to override the implicit timeouts that exist in vttablet. However, this mode should be used judiciously as it can block shutdown and reparent commands.

The general convention is to send OLTP queries to REPLICA tablet types, and OLAP queries to RDONLY.

Can I choose between primary and replica for query routing? #

You can qualify the keyspace name with the desired tablet type using the @ suffix. This can be specified as part of the connection as the database name, or can be changed on the fly through the USE command.

For example, ks@primary will select ks as the default keyspace with all queries being sent to the primary. ks@replica will load balance requests across all REPLICA tablets, and ks@rdonly will choose RDONLY.

You can also specify the database name as @primary, @replica etc., which means that no default keyspace is specified, but that the requests are for the specified tablet type.

If no tablet type is specified, then VTGate chooses its default, which can be overridden with the --default_tablet_type command line argument.

Can I address a specific shard if I want to? #

If necessary, you can access a specific shard by connecting to it using the shard-specific database name, or issuing a USE statement to switch to it if already connected to vtgate.

For a keyspace ks and shard -80, you would use the database name ks:-80. This is called manual shard targeting. Please note that shard targeting is considered an advanced feature and should be used with caution. In particular, it is possible to insert rows into the wrong shard by using shard targeting.

Can I set a session variable query timeout? #

If you would like something similar to [max_execution_time](https://dev.mysql.com/blog-archive/server-side-select-statement-timeouts/) you can set the vttablet command line flag as follows: -queryserver-config-query-timeout=15. This is set in seconds.

You can also specify a query comment like select /*vt+ QUERY_TIMEOUT_MS=1000 */ ...

If you choose to set the vttablet command line flag the time you choose will set the absolute max time. The query comment can only override the timeout to a lower value.

This timeout via SQL query comments has the following limitations/caveats:

• You need to prevent your SQL client from stripping the comments before sending to the server (the MySQL CLI strips comments by default)
• You need to disable query normalization in vtgate (--normalize_queries false); to allow the comment to reach vttablet.
• It only works for SELECT statements today, this might change in the future.

Can I increase the resource pool timeout for streaming requests? #

Yes. You can adjust the vttablet flag for this. For example: --queryserver-config-stream-pool-timeout=1s.