Shared caching

In the default startup mode for qdb, both shared caching and exclusive mode are enabled. You can change this behavior as follows:
  • To disable shared caching, use the -D command-line option.
  • When shared caching is enabled, qdb reserves exclusive privileges for writing to the database. To allow other applications to use the database files, use the -A option.
Note:
The qdb utility exits immediately if it is started with shared cache disabled but exclusive mode enabled. For example: 
# qdb -v -D -otempstore=/dev/shmem -Rset
qdb: Exclusive locking mode requires that shared cache
be enabled

Advantages of shared caching

Shared caching improves performance times and reduces the total amount of memory required for database connections by having multiple connections share the same memory cache.

For example, without shared caching, if 1 MB of memory is required for each database connection, 40 connections require 40 MB of memory. With shared caching, these 40 connections could share a common memory cache of, say, 25 MB (or another size determined by your environment and performance requirements). Furthermore, there is no duplication in memory, so you may be able to hold all or most of the database, greatly reducing the need for disk I/O.

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