Write Queries

UPDATE and DELETE Queries

The WHERE clause in an UPDATE or DELETE query is optimized the same way as the WHERE clause in a SELECT query. If the predicate matches the shard key exactly then the query is routed to a single partition.

INSERT Queries

SingleStore executes INSERT queries by analyzing the insert values relevant to the shard key and routing the query to the corresponding partition. For example, INSERT INTO a (a1, a2, a3) VALUES (1, 2, 3) would compute the hash value of (1, 2) and map this value to the appropriate partition.

If you are bulk inserting data with INSERT queries, then you should take advantage of the multi-insert syntax: INSERT INTO a (a1, a2, a3) VALUES (1, 2, 3), (2, 3, 4), .... The aggregator node will chop up the multi-insert into single-partition insert queries and run them in parallel across the cluster. This technique enables your application to combat the inherent latency of running in a distributed system.

When a multi-insert statement is executed, SingleStore uses two steps to commit the transaction:

• Step one, where each leaf node validates their portion of the statement and acknowledges that they are ready to commit, and

• Step two, where each leaf node actually commits the transaction.

Both steps are necessary to ensure that each leaf node partition successfully receives and executes their portion of the insert statement. If an error occurs, the entire transaction is rolled back across the cluster.

For example, consider a cluster with two leaf nodes and four partitions total. When a multi-insert statement is executed against the cluster’s aggregator node, each leaf node validates its portion of the statement and prepares to commit the transaction on its two partitions. When all leaf nodes have acknowledged their readiness, the aggregator node notifies them to commit the transaction. Finally, the transaction is committed, and the data is successfully inserted.