Category: Columnstore

Koen Verbeeck discusses what updates do to clustered columnstore indexes:

Turns out the majority of the rows belonged to the second scenario. Whoops. The initial run took a little over 20 hours. Not exactly rocket speed. The problem was that for each period, a large number of rows in the clustered columnstore index (CCI) had to be updated, just to set the range of the interval. Updates in a CCI are expensive, as they are split into inserts and deletes. Doing so many updates resulted in a heavily fragmented CCI and with possibly too many rows in the delta storage (which is row storage).

Read the whole thing.  Koen links to a Niko Neugebauer post, which you should also read.  After that, read my warning on trickle loading.  The major querying benefits you get from clustered columnstore indexes is great, but it does come at a cost when you aren’t simply inserting new rows.

Niko Neugebauer discusses LOB support in SQL Server vNext:

In the upcoming version of SQL Server (for the moment known as SQL Server vNext), Microsoft has finally announced the upcoming support for the LOBs within Columnstore Indexes – thus enabling the usage of the NVARCHAR(MAX), VARCHAR(MAX), and VARBINARY(MAX) data types on the tables with Columnstore Indexes that include those columns.

For the tests, I have decided to spin a Virtual Machine in Azure with an installation of the currently available CTP1 of the SQL Server vNext, which has a version 14.0.1.126.

Read the whole thing.  It’s hard to tell at this point if these are bugs, incomplete functionality, or what, so it’ll be interesting to track changes over the CTPs.

I have a post on an issue I had with loading columnstore data:

In this design, I have data coming from the transactional system, undergoing some ETL processing, and going into a staging table on the warehouse.  From there, I perform the remainder of the ETL work and insert into a rowstore table.  This rowstore table has the same attribute names and data types as the columnstore table, but instead of having a clustered columnstore index, it has a standard B-tree index and can have additional non-clustered indexes.  From there, I expose the combination table using a view which simply unions the two sets of data so the application doesn’t have to see rowstore versus columnstore tables.

If you’re doing nightly insertions, results tend to be a lot better.  But if you need close-to-but-not-quite real-time data, there are still ways to solve the problem.

Niko Neugebauer has released the latest version of his Columnstore Index Scripts Library:

Another happy release of the CISL (Columnstore Indexes Script Library) is live – this time it is 1.4.0!

This release is focusing on the addition of the Extended Events, so that a user of CISL can easily set up the events for each of the SQL Server (2012,2014,2016) or Azure SQL Database versions.

This is an open source library which I recommend if you deal with columnstore indexes in any fashion.

Niko Neugebauer continues his columnstore series by looking at columnstore insert logging in SQL Server 2016 versus 2014:

Ladies and gentlemen! That’s quite a difference to SQL Server 2014!
We better check the total length of the transaction log to see the final result: 384.032 bytes! Ok, that is significantly more than for the rowstore heap table for sure, but what about the comparison to the SQL Server 2014 ? Did this minimal logging bring any improvement ?
Well … 🙂
In SQL Server 2014 we had 1.255.224 bytes spent on the transaction log – meaning over 1.2 MB, meaning around 3 times more, for the Delta-Store insertion! For such a simple table, this is a huge improvement, but let’s take a look at the total length of the transaction log entries in both environments (SQL Server 2014 & SQL Server 2016)

This is worth a careful read.  If you’ve spent time working with 2014 clustered columnstore indexes, there are a few changes which might affect you.  The most interesting thing for me was that the deltastore is no longer page compressed.