MULTISHARD_QUERY_DATA

1.210 MULTISHARD_QUERY_DATA_CONSISTENCY

MULTISHARD_QUERY_DATA_CONSISTENCY enables you to specify a data consistency setting for multi-shard queries.

Property	Description
Parameter type	String
Syntax	`MULTISHARD_QUERY_DATA_CONSISTENCY = { STRONG \| SHARD_LOCAL \| DELAYED_STANDBY_ALLOWED }`
Default value	`STRONG`
Modifiable	`ALTER SESSION`, `ALTER SYSTEM`
Modifiable in a PDB	Yes
Basic	No
Oracle RAC	The value of this parameter can be different on different Oracle RAC instances.

You can use MULTISHARD_QUERY_DATA_CONSISTENCY to avoid the cost of SCN synchronization when executing multi-shard queries across shards, which can be globally distributed.

MULTISHARD_QUERY_DATA_CONSISTENCY can be set at the system level or the session level.

The values that can be set for MULTISHARD_QUERY_DATA_CONSISTENCY are:

STRONG: With this setting, SCN synchronization is performed across all shards, and data is consistent across all shards. This setting provides global consistent read capability. This is the default value.
SHARD_LOCAL: With this setting, SCN synchronization is not performed across all shards. Data is consistent within each shard. This setting provides the most current data.
DELAYED_STANDBY_ALLOWED: With this setting, SCN synchronization is not performed across all shards. Data is consistent within each shard. This setting allows data to be fetched from Data Guard standby databases when possible (for example, depending on load balancing), and may return stale data from standby databases.