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Category: Columnstore

CISL

Niko Neugebauer talks about the Columnstore Indexed Scripts Library:

Around 3.5 Months ago in September of 2015, I have announced the first public release of the CISL – Columnstore Indexes Scripts Library, which allows to have a deeper insight into the database that uses or can use Columnstore Indexes.
Since that, I have released 4 more “point releases” with bug fixes and new features, I have greatly expanded the support of SQL Server with inclusion of SQL Server 2012, SQL Server 2016 and Azure SQLDatabase.

If you use columnstore indexes, you absolutely want to get this.  Also, there’s a brand new update out.

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Trace Flag 834 And Columnstore

Chris Bell warns us against having Trace Flag 834 turned on in an instance which contains columnstore indexes:

[I]t is not recommended to have trace flag 834 on when using columnstore indexes in your databases.

Since the 834 trace flag is a global level flag, and columnstores are in individual databases I wrote the script below to go through and check if you ave any columnstore indexes, and then check if the trace flag is enabled.

Chris also has a helpful script to see if your instance has this issue.

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In-Memory Analytics

Sunil Agarwal introduces us to In-Memory Analytics, forthcoming in SQL Server 2016:

SQL Server 2016 has significant advancements over SQL Server 2014 for In-Memory analytics. Some highlights are functionality (e.g. ability to create traditional nonclustered index to enforce PK/FK), performance (e.g. addition of new BatchMode operators, Aggregate pushdown), Online index defragmentation, and supportability (e.g. new DMVs, Perfmon counters and XEvents).

His post talks a little bit about in-memory, but focuses more on clustered columnstore indexes.  I like that columnstore indexes are getting V3 improvements, and I think they’ll be even more useful.  Whether the “in-memory” part becomes useful is a different question; I personally have seen a very limited adoption of In-Memory OLTP (and a few huge bugs for the people brave enough to try it).

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Increased Delta Store Size For NCIs

Niko Neugebauer, in part 73 of his ongoing columnstore index series:

This result was observed right after the finish of the loading script, where we can clearly see 4 Delta-Stores for 10 Million Rows. 3 of the Delta-Stores are Closed and 1 Delta-Store is Open, which is an absolutely impossible combination if we think about Clustered Columnstore Indexes, where one would expect to have 10 Compressed Row Groups or 10 Delta-Stores (9 Closed & 1 Open).
If you take a more detailed look at the associated sizes of the closed Delta-Stores, you will see that they increase each time a new Delta-Store is being used. For example, the first one is capped at 1.048.567 Rows, the second one is capped at 2.097.152 and the last closed Delta-Store is set to 4.193.904 Rows – meaning that the size is being constantly doubled.

I’d like to see this as the first step toward expanded sizes for compressed rowgroups.

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