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.

Related Posts

Columnstore And Merge Replication

Niko Neugebauer tests whether merge replicated tables can use columnstore indexes: Adding this table to the publication will end up with the following, self-explaining error message, being very clear that the Clustered Columnstore Indexes are not supported for the Merge Replication[.] There is no surprise here, as the same Clustered Columnstore Indexes are not supported […]

Read More

Trace Flag 834 And Columnstore Tables

Joe Obbish shows how trace flag 834 can solve a bottleneck when inserting into tables with clustered columnstore indexes: In my experience, when we get into a situation with high memory waits caused by too much concurrent CCI activity all queries on the server that use a memory grant can be affected. For example, I’ve […]

Read More


November 2015
« Jan Dec »