Performance of SQL Server 2014 Columnstore Archival Mode

I blogged about this in not a whole lot of detail a couple of month ago, but as an add to my recent testing of columnstore index update and insert performance, I decided to take another shot at testing the next Columnstore Archival mode of compression in SQL 2014 CTP2. What this allows to do is take either an entire columnstore index (really bad idea) or selected relatively unused partitions of our columnstore index, and compress them into an even smaller archive than a typical columnstore index. Microsoft, per conversations I had at PASS Summit mentioned seeing compression gains of up to 26%.

The Test

Like I did in my insert and update testing, I used the Make Big AdventureWorks script, which you can download here courtesy of Adam Machanic’s (b|t). Specifically, my focus was in and around the BigTransaction table. I partitioned the table based on date. Before I compressed, the partitions were the following sizes:

Table

Partition

Rows

Data KB

BigTransaction_Reg_Columnstore

1

3774500

29144

BigTransaction_Reg_Columnstore

2

3152574

24200

BigTransaction_Reg_Columnstore

3

2909218

22200

BigTransaction_Reg_Columnstore

4

2812282

21720

BigTransaction_Reg_Columnstore

5

2660245

20664

BigTransaction_Reg_Columnstore

6

2627890

30008

BigTransaction_Reg_Columnstore

7

2461343

28064

BigTransaction_Reg_Columnstore

8

2568732

29352

BigTransaction_Reg_Columnstore

9

8296817

52512

 

After I rebuilt partitions 1-5 with archival Columnstore compression, I saw the following savings in compression:

Table

Partition

Rows

Data KB

Compression %

BigTransaction_Arch_Columnstore

1

3774500

42480

31.39%

BigTransaction_Arch_Columnstore

2

3152574

35552

31.93%

BigTransaction_Arch_Columnstore

3

2909218

32840

32.40%

BigTransaction_Arch_Columnstore

4

2812282

32072

32.28%

BigTransaction_Arch_Columnstore

5

2660245

30520

32.29%

BigTransaction_Arch_Columnstore

6

2627890

30008

N/A

BigTransaction_Arch_Columnstore

7

2461343

28064

N/A

BigTransaction_Arch_Columnstore

8

2568732

29352

N/A

BigTransaction_Arch_Columnstore

9

8296817

52512

N/A

Average

     

32.06%

 

So for the partitions I rebuilt, I see an average space savings of 32%, but at what cost select performance?

Select Performance

The range query I did—selecting average transaction cost and date, with a group by on the date, with a filter on to only pull in dates in the archived partitions. In terms of pure time to execute the query, the columnstore archival query ran about 18% longer, however it consumed 51% more CPU time. Compression is CPU costly, and the more we compress data, the more CPU cycles are required to uncompress. One other point of note, when I partitioned the table (with either form of compression) I see a lot more logical reads for the same query plans. Here the numbers where around 85k and 120k, but if I run the same query against an unpartitioned table with columnstore the count is much closer to 40k. Aaron Bertrand (b|t) pointed out that this might be related to a bug with statistics IO.

 

 

 

 

 

So there is some benefit to this feature—using it as a cold archive, you can make gains in storage, potentially up to 30+% with a relatively minor penalty for querying. It should be best utilized on data that you don’t plan on accessing on a regular basis.

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About Joseph Dantoni
A DBA, cyclist, cook (who likes to play chef occasionally)

One Response to Performance of SQL Server 2014 Columnstore Archival Mode

  1. Pingback: Resources from Columnstore Index Presentation | The SQL Herald

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