PREFETCH_MODE Query Option (CDH 5.8 or higher only)
Determines whether the prefetching optimization is applied during join query processing.
Type: numeric (0, 1) or corresponding mnemonic strings (NONE, HT_BUCKET).
Default: 1 (equivalent to HT_BUCKET)
Added in: CDH 5.8.0 / Impala 2.6.0
The default mode is 1, which means that hash table buckets are prefetched during join query processing.