Throughout our previous posts we have mentioned various session level statistics that are available to help identify what is actually going on with Database In-Memory. Since these statistic definitions didn’t make it into the Reference manual I was asked recently if there is a list anywhere that defines what these statistics are. Since there isn’t I thought I’d post a summary of the popular statistics that we’ve mentioned in the blog and that you might want to know about.
| Name | Description |
| IM scan rows optimized | Number of rows that were skipped (because of storage index pruning) or that weren’t accessed due to aggregations with predicate push downs |
| IM scan rows projected | Number of rows returned to the upper layer |
| IM scan rows | Number of rows scanned in all IMCUs |
| IM scan rows valid | Number of rows scanned in all IMCUs after applying valid vector |
| IM scan CUs no memcompress IM scan CUs memcompress for dml IM scan CUs memcompress for query low IM scan CUs memcompress for query high IM scan CUs memcompress for capacity low IM scan CUs memcompress for capacity high |
Number of times IMCUs of each mecompress type were touched |
| IM scan CUs columns accessed | Number of columns accessed by a scan |
| IM scan CUs invalid or missing revert to on disk extent | Number of on disk extents accessed due to missing or invalid IMCUs |
| IM scan CUs pruned | Number of IMCUs with no rows passing min/max |
| IM scan segments minmax eligible | Number of IMCUs that are eligible for min/max pruning |
| IM scan segments disk | Number of times a segment marked for in-memory was accessed entirely from the buffer cache/direct read |
| IM scan CUs predicates applied | Number of min/max predicates applied |
| IM scan CUs predicates optimized | Number of IMCUs where either all rows passed min/max or no rows passed min/max |
| IM scan CUs predicates received | Number of min/max predicates received |
| IM populate segments requested | Number of population tasks for in-memory segments |
| table scan disk IMC fallback | Number of rows in blocks scanned from buffer cache/direct read where an IM scan was possible |
| table scan disk non-IMC rows gotten | Number of rows in blocks scanned from buffer cache/direct read where an IM scan was not possible |
| table scans (IM) | Number of segments scanned in-memory |
| session logical reads – IM | Number of blocks scanned in an IMCU |
Original publish date: August 28, 2015