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 and this option applies to all filesystem-based tables. 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.
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: