Hi Yuan, VSSB scan returns a row for each rowID in a given set of rowIDs. When the rowID is not present an indication that the row is not found is returned. Usually VSSB scan is chosen by Trafodion optimizer in a case of a nested join when the left side of the join can send all the columns that are part of the rowID of the right table to the right side. This is implemented via LIST<Get> Hbase API.
Scan returns a set of rows for a given rowID range or for the partial leading rowID columns. Scan is chosen by Trafodion optimizer to build the hash of the inner (or right) table or select the rows of the outer table in hash join. Scan can also be chosen in a single table select. This is implemented via ResultScanner APIs. The above is not a complete set of decision pointers of the Trafodion optimizer to choose between vssb_scan and scan. Selva -----Original Message----- From: Liu, Yuan (Yuan) [mailto:[email protected]] Sent: Tuesday, January 2, 2018 6:19 PM To: [email protected] Subject: trafodion_vsbb_scan vs trafodion_scan? Hi Trafodioneers, Recently I saw trafodion_vsbb_scan and trafodion_scan in the same explain plan, can anyone help explain what is the difference of each other? LC RC OP OPERATOR OPT DESCRIPTION CARD ---- ---- ---- -------------------- -------- -------------------- --------- 19 . 20 root 1.09E+013 18 . 19 esp_exchange 1:14(hash2) 1.09E+013 16 17 18 tuple_flow 1.09E+013 . . 17 trafodion_load h TEST_LP2 1.00E+000 15 . 16 sort 1.09E+013 12 14 15 nested_join 1.09E+013 13 . 14 probe_cache 1.89E+005 . . 13 trafodion_vsbb_scan DM_FUNCTION_LOCATION 1.89E+005 11 2 12 left_hybrid_hash_joi 5.78E+007 8 10 11 left_nested_join 9.23E+005 9 . 10 probe_cache 5.69E+001 . . 9 trafodion_vsbb_scan JL_POWER_MEASURE 5.69E+001 7 . 8 esp_exchange 14(hash2):14(hash2) 1.62E+004 6 4 7 hybrid_hash_join 1.62E+004 5 . 6 esp_exchange 14(hash2):128(hash2) 7.77E+006 . . 5 trafodion_scan JL_CURRENT_MEASURE 7.77E+006 3 . 4 esp_exchange 14(rep-b):1 2.58E+002 . . 3 trafodion_scan B_TRANFORMER_MEAS_R 2.58E+002 1 . 2 esp_exchange 14(hash2):128(hash2) 6.94E+006 . . 1 trafodion_scan JL_VOLTAGE 6.94E+006 Best regards, Yuan
