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Enabling Real-Time Analytics With Database In-Memory

Popular Statistics with Database In-Memory

Andy Rivenes
Product Manager

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

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