SYNC_DDL Query Option

When enabled, causes any DDL operation such as CREATE TABLE or ALTER TABLE to return only when the changes have been propagated to all other Impala nodes in the cluster by the Impala catalog service. That way, if you issue a subsequent CONNECT statement in impala-shell to connect to a different node in the cluster, you can be sure that other node will already recognize any added or changed tables. (The catalog service automatically broadcasts the DDL changes to all nodes automatically, but without this option there could be a period of inconsistency if you quickly switched to another node, such as by issuing a subsequent query through a load-balancing proxy.)

Although INSERT is classified as a DML statement, when the SYNC_DDL option is enabled, INSERT statements also delay their completion until all the underlying data and metadata changes are propagated to all Impala nodes. Internally, Impala inserts have similarities with DDL statements in traditional database systems, because they create metadata needed to track HDFS block locations for new files and they potentially add new partitions to partitioned tables.

Note: Because this option can introduce a delay after each write operation, if you are running a sequence of CREATE DATABASE, CREATE TABLE, ALTER TABLE, INSERT, and similar statements within a setup script, to minimize the overall delay you can enable the SYNC_DDL query option only near the end, before the final DDL statement.

Type: Boolean; recognized values are 1 and 0, or true and false; any other value interpreted as false

Default: false (shown as 0 in output of SET statement)

Related information:

DDL Statements

Parent topic: Query Options for the SET Statement