Index scan fails for long IN lists delivering very many rows from index
Details
| Detail name | Value |
|---|---|
| Changelog Number | 5245 |
| Type | Bug |
| Status | Resolved |
| Affected Versions | EXASOL 6.0.3 |
| Fix Versions | EXASOL 6.0.7 |
| Resolution Date | 2017-11-14 |
To improve scan performance the query optimizer may choose to use an existing index on a scan table filter expression. If the index returns very many rows for certain expressions (e.g. IN list elements), such large jobs are executed multi threaded allowing a higher CPU utilization.
Under the following conditions the index scan may fail
1) More than 1024 index keys (IN list elements)
2) Some keys deliver more than 100.000 rows from the index
The bug lies therein that under the combination of above conditions the multi threaded execution of large index scan jobs could crash.
Workaround
Disable the multi threaded execution of large index jobs
-largeKeySplitting=0
The parameter affects index scans, joins and exists. Query performance may be slightly affected.
