LATCH_EX Waits on Resource METADATA_SEQUENCE_GENERATOR

We have a process that generates an inventory report. On the client side, the process splits of a configurable number of worker threads to build a chunk of data for the report that corresponds to one store out of many (potentially thousands, typically dozens). Each worker thread calls a web service that executes a stored procedure.

The database process for processing each chunk gathers a bunch of data into a #Temporary table. At the end of each processing chunk, the data is written to a permanent table in tempdb. Finally, at the end of the process, one thread on the client side requests all the data from the permanent tempdb table.

The more users that run this report, the slower it gets. I analyzed the activity in the database. At one point, I saw 35 separate requests all blocked at one point in the process. All these SPIDs had on the order of 50 ms waits of type LATCH_EX on resource METADATA_SEQUENCE_GENERATOR (00000010E13CA1A8). One SPID has this resource, and all the others are blocking. I did not find anything about this wait resource on a web search.

The table in tempdb that we are using does have an IDENTITY(1,1) column. Are these SPIDs waiting for the IDENTITY column? What methods could we use to reduce or eliminate the blocking?

The server is part of a cluster. The server is running 64-bit SQL Server 2012 Standard Edition SP1 on 64-bit Windows 2008 R2 Enterprise. The server has 64 GB RAM and 48 processors, but the database can only use 16 because it is the standard edition.

(Note that I'm not thrilled by the design of using a permanent table in tempdb to hold all this data. Changing that would be an interesting technical and political challenge, but I'm open to suggestions.)

UPDATE 4/23/2013

We've opened a support case with Microsoft. I'll keep this question updated as we learn more.

UPDATE 5/10/2013

The SQL Server support engineer agreed that the waits were caused by the IDENTITY column. Removing the IDENTITY eliminated the w

(Updated February 2019)

This is an old post, that said I've finally managed to convince Microsoft that the very fact this happens is indeed a defect.

Update: MS Confirmed the defect and assigned it a bug # of 12628722.

I had seen this post this past November 2018 when we to began to suffer much the same after we'd upgraded from Sql Server 2005 to Sql Server 2017. A 3.3 million row table that used to take 10 seconds to bulk insert suddenly started taking 10 minutes on tables with Identity columns.

Turns out there are two issues behind this:

• Microsoft changed the behavior in Sql Server 2014 to force Bulk Inserts to run parallelized - in prior versions Bulk Inserts were given a Serialized plan.

• Once running in parallel on our 32 core box, the engine spent more time with the cores locking each other than actually doing the work.

Took me 4 weeks but just after the holidays I got a belated present from Santa - confirmation that the issue was indeed a defect.

There are a few possible workarounds that we found until this is fixed:

• Use Option (MaxDop 1) in the query to turn the bulk insert back into a serialized plan.

• Mask the Identity column by casting it (e.g. Select Cast(MyIdentityColumn As Integer) As MyIdentityColumn)

• this prevents the identity property from being copied when using SELECT...INTO

• Remove the identity column as described above.

• Change the database compatibility mode to Sql Server 2012 or lower to re-establish a serialized plan.

Update:
The fix MS will be implementing will be to return these sorts of Inserts back to using a Serialized plan. This is planned for Sql Server 2017 CU14 (no news on other versions of Sql Server - sorry!).
When implemented, Trace Flag 9492 will need to be turned on, either at the server level, or via DBCC TraceOn.

StackExchange Database Administrators Q#40459, answer score: 7