When you try to build an index (by using CREATE INDEX or ALTER INDEX) on a spatial data type of a large table in Microsoft SQL Server 2012 or SQL Server 2014, the contention is high on the CMEMTHREAD wait type, and the performance of SQL Server decreases.
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A CMEMTHREAD wait type indicates the wait on the internal, thread-safe memory objects. Higher levels of query parallelism may trigger the wait that leads to decreased performance of the spatial activity.
This fix partitions the CMEMTHREAD that associates with the "Spatial Memory Object" by using NUMA node partitioning. This reduces the worker activity concurrency to the number of schedulers active on a single node. For systems with higher levels of schedulers per node, trace flag –T8048 can be used to further partition all memory objects that allow partitioning by scheduler. Use the trace flag carefully, as it introduces a small amount of memory overhead to all NUMA node-partitioned memory objects.
Note The spatial memory object is created when the SqlServerSpatial110.dll is loaded into the SQL Server process address space. In most conditions, this requires a restart of the SQL Server process in order to apply the trace flag effects.
The CMEMTHREAD wait type is incremented for any thread safe memory object wait, not just the spatial object. The following XEvent session definition and use of public symbols can be used to identify the specific code line that is generating CMEMTHREAD waits:CREATE EVENT SESSION wait_stacks
ADD EVENT sqlos.wait_info
where opcode = 1 -- wait completed
and wait_type = 191 -- CMEMTHREAD
add target package0.asynchronous_bucketizer (SET source_type = 1, source = 'package0.callstack'),
add target package0.ring_buffer (SET max_memory = 4096)
With (MAX_DISPATCH_LATENCY = 1 SECONDS)
alter event session wait_stacks on server state = start
Run the repro
select event_session_address, target_name, execution_count, cast (target_data as XML)
from sys.dm_xe_session_targets xst
inner join sys.dm_xe_sessions xs on (xst.event_session_address = xs.address)
where xs.name = 'wait_stacks'
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.