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From Selva Govindarajan <selva.govindara...@esgyn.com>
Subject RE: trafodion_vsbb_scan vs trafodion_scan?
Date Wed, 03 Jan 2018 05:26:16 GMT
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:yuan.liu@esgyn.cn] 
Sent: Tuesday, January 2, 2018 6:19 PM
To: dev@trafodion.incubator.apache.org
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


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