Skip Chunks Using Dictionary Thread Count

The skipChunksUsingDictThreads flag sets the number of threads the dictionary chunk filter uses to read chunk dictionaries. The filter is controlled by skipChunksUsingDictColumn, and this flag has no effect when that filter is off.

Dictionaries are read in batches across the pool rather than one chunk at a time, which is where most of the filter’s benefit on a wide scan comes from.

The following describes the skipChunksUsingDictThreads flag:

• Data type - size_t

• Default value - 8

• Allowed values - Any positive integer, in threads

Raising the value above the default was measured to give no further improvement. The flag is developer-only, so a session must have developerMode set before it can be changed.