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Chapter 14
Using Disk Stores to Persist Data
You can persist table data to disk as a backup to the in-memory copy, or overflow table data to disk when memory use
gets too high.
Overview of Disk Stores
The two disk store options, overflow and persistence, can be used individually or together. Overflow uses disk
stores as an extension of in-memory table management for both partitioned and replicated tables. Persistence
stores a redundant copy of all table data managed in a peer.
See Evicting Table Data from SQLFire on page 187 for more information about configuring tables to overflow
to disk.
Data Types for Disk Storage
Disk storage is available for these data types:
• Table data. Persist and/or overflow table data managed in SQLFire peers.
• Gateway sender queues. Persist gateway sender queues for high availability in a WAN deployment. These
queues always overflow.
• AsyncEventListener and DBSynchronizer queues. Persist these queues for high availability. These queues
always overflow, and can be persistent.
You can store data from multiple tables and queues in a single disk store.
Creating Disk Stores and Using the Default Disk Store
You create named disk stores in the data dictionary using the CREATE DISKSTORE DDL statement. Individual
tables can then specify named disk stores in their CREATE TABLE DDL statements to use the stores for
persistence and/or overflow. You can store data from multiple tables and queues in the same named disk store.
See Guidelines for Designing Disk Stores on page 83.
Tables that do not name a disk store but specify persistence or overflow in their CREATE TABLE statement use
the default disk store. The location of the default diskstore is determined by the value of the sys-disk-dir
boot property. The default disk store is named SQLF-DEFAULT-DISKSTORE.
Gateway sender queues, AsyncEventListener queues, and DBSynchronizer queues can also be configured to use
a named disk store. The default disk store is used if you do not specify a named disk store when creating the
queue. See CREATE GATEWAYSENDER on page 469 or CREATE ASYNCEVENTLISTENER on page 462.
Peer Client Considerations for Persistent Data
Peer clients (clients started using the host-data=false property) do not use disk stores and can never persist
the SQLFire data dictionary. Instead, peer clients rely on other data stores or locators in the distributed system
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