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This wait type (and the other HT* waits) is when a thread is waiting for access to the shared hash table used during batch-mode processing. SQL Server 2012 used to use a hash table per thread and SQL Server 2014 now uses a shared hash table. This change was made to reduce the amount of memory required for the hash table, but comes at the expense of these waits when synchronizing access to the hash table. Typically these waits occur when queries involve columnstore indexes, but they can also occur without columnstore indexes being involved if a hash operator runs in batch mode.
(Books Online description: N/A)
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Added in SQL Server version:
Removed in SQL Server version:
Extended Events wait_type value:
Maps to the HASH_TABLE_DELETE map_value in sys.dm_xe_map_values.
The map_key value in sys.dm_xe_map_values is 195 in 2014 RTM. After 2014 RTM, you must check the DMV to get the latest value as some map_key values have changed in later builds.
I have heard of this wait type occurring during updates to clustered columnstore indexes when the index has a lot of deleted rows per rowgroup, which can be fixed by rebuilding the index.
Known occurrences in SQL Server (list number matches call stack list):
Abbreviated call stacks (list number matches known occurrences list):