[TRAFODION-2282] Optimizer histogram cache is sometimes never refreshed

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.1-incubating
• Fix Version/s: 2.1-incubating
• Component/s: sql-cmp
• Environment: All
• Assignee: Dave Birdsall
• Reporter: Dave Birdsall
• Created: 12/Oct/16 23:35
• Updated: 15/Sep/18 07:31
• Resolved: 19/Oct/16 21:48

Description

Here's the scenario:

In session 1, create a table T1 and populate it with, say, 200000 or more rows.

In session 2, prepare a query that selects from T1. For example, select A,COUNT FROM T1 GROUP BY A. The query should compile fine, but you should see missing statistics warning messages (warning codes 6007 and 6008).

In session 1, do "update statistics for table t1 on every column"

In session 2, prepare other queries over a period of time. What should happen is that after about an hour, the Optimizer decides to refresh the histograms. However, due to a bug, it might never do so. So, the missing statistics warnings (6007, 6008) never go away. Worse, the prepares never benefit from the statistics so plan choice may be poor.

Issue Links

• links to: GitHub Pull Request #766
• links to: GitHub Pull Request #771
• links to: GitHub Pull Request #792