Examine the value of Current Indexer Queue Size in the Indexing Manager node of JConsole to check the backlog state or the number of Assets that are pending for preview generation. To clear the backlog, click once on clearIndexerQueue button under the Operations tab of the Indexing Manager node in JConsole. This will clear the current queue of assets pending indexing.

The MaxActive value in IndexerThreadPool node of JConsole specifies the number of threads currently handling indexing requests. The default value of 2 may be increased to speed up indexing by allocating more resources.

You can also query for Assets pending for indexing. The attribute Indexing Status displays the state of preview/thumbnail generation of assets. For assets in the indexing queue, its value is set to Pending. You can query/count for assets whose Indexing Status value is Pending.