Major Description
If I have a Trafodion table salted into 2 partitions, I can induce a parallel plan on that table using a cardinality hint. For example:
CREATE TABLE TRAFODION.SEABASE.ADEF
(
ROW_ID VARCHAR(100) CHARACTER SET ISO88591
COLLATE DEFAULT NO DEFAULT NOT NULL NOT DROPPABLE NOT SERIALIZED
, COLUMN_DETAILS VARCHAR(10000) CHARACTER SET ISO88591
COLLATE DEFAULT NO DEFAULT NOT NULL NOT DROPPABLE NOT SERIALIZED
, PRIMARY KEY (ROW_ID ASC)
)
SALT USING 2 PARTITIONS
ATTRIBUTES ALIGNED FORMAT
;
>>prepare s1 from select column_details,count
> from adef << cardinality 1e8 >>
+> group by column_details;
— SQL command prepared.
>>explain options 'f' s1;
LC RC OP OPERATOR OPT DESCRIPTION CARD
---- ---- ---- -------------------- -------- -------------------- ---------
4 . 5 root 2.00E+000
3 . 4 hash_partial_groupby 2.00E+000
2 . 3 esp_exchange 1:2(hash2) 2.00E+000
1 . 2 hash_partial_groupby 2.00E+000
. . 1 trafodion_scan ADEF 1.00E+008
— SQL operation complete.
However, if I have a native HBase table split into two regions, the same cardinality hint does not produce a parallel plan:
>>prepare s2 from select column_details,count
> from hbase."ROW"."def" << cardinality 1e8 >>
+> group by column_details;
— SQL command prepared.
>>explain options 'f' s2;
LC RC OP OPERATOR OPT DESCRIPTION CARD
---- ---- ---- -------------------- -------- -------------------- ---------
2 . 3 root 2.00E+000
1 . 2 hash_groupby 2.00E+000
. . 1 hbase_scan def 1.00E+008
— SQL operation complete.
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