FYI ...

Craving a bit of update statistics low performance?

Update statistics low gathers information about an index by traversing across the leaves of the btree. Prior to 11.70.xC3, Informix would
read each leaf page individually without the use of any readahead functionality. This meant that for each leaf page encountered, unless
the leaf page happened to be in the bufferpool cache, the update statistics low process would have to wait for that leaf page to be
brought into the bufferpool cache before processing it and moving to the next leaf page.

With the introduction of automatic readahead (also coming in 11.70.xC3), we’ve enhanced update statistics to utilize the same
readahead functionality that is provided to user queries that do range scans. This dramatically improves the performance. In the lab
testing shows a 300% speed up. Of course, your milage will vary.
What do you have to do to take advantage of this?

Remove from your ONCONFIG file the onconfig parameters RA_PAGES and RA_THRESHOLD. Then set AUTO_READAHEAD to 1.
AUTO_READAHEAD 1

BUT WAIT… There’s more.

We’ve also added a new algorithm for gathering statistics to use sampling which avoids having to traverse the entire btree. We’ve gone
to great lengths to make sure we handle skewed data with a proprietory algorithm. That 300% speed jumps to 2000% and best of all, unless the data is skewed, the time it takes to get stats on and index remains fairly constant regardless of the size of the index. That 1M page index will take you about 30s-50s to get stats. Same for that 5M page index.

No more waiting hours for update statistics to complete. What do you have to do to take advantage of this?
onmode -wm SQL_FEAT_CTRL=0

Enjoy!
Mr.GrumpyPants

Kind regards,
Vadim Golovsky.