1.200 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.

See Also:

Using Oracle Sharding for more information about specifying consistency levels in a multi-shard query