HCC Compression Degradation Issue – Demo

We’ve seen the really nice degree of compression we’ve achieved against my hybrid compressed table. Now we’ll just do some DML against it.

Now I’ll go to my basic compressed table or the deduplicated table. It’s a pretty bad timing difference there. Now let’s move on to the HCC table, and you can see there’s definitely a performance hint when compared to the non-compressed data.

Now, whether that’s likely to be a problem, I simply don’t know, but it would depend on the nature of your application. Clearly, this is a pretty big hint, so you need to think quite hard about which tables to apply HCC to. It may not be a problem for many sites.

One more check we need to do is to see the effects on space usage. So I’ll just gather some fresh statistics for all three tables. Now, previously, we were achieving about two for one on basic compression and it’s 30 for one on hybrid columnar compression.

Now we see the really bad news. My basic compressed table has about doubled in size. My uncompressed table has remained pretty much — in fact, identical to what it was before, and my HCC table has now become the size of the uncompressed table plus the seven blocks there was originally, and this is serious. The degradation and compression of DML is something that many sites will definitely need to think about.

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