merge all-shards results

[cholgyu-kang]

problem

The ResultSet of all-shards query is just union-all of each shard ResultSet

• aggregation query: ex) select count(*) from foo;
  expect> 1 row ResultSet
  current> multiple rows ResultSet

• order-by query: ex) select * from foo order by 1;
  expect> fully ordered ResultSet
  current> partially ordered ResultSet for each shard result

suggestion

merge COUNT(), SUM(), MIN(), MAX(), AVG() query results

step 1

specify merging rule by API

• RyeStatement.mergeRs(int operation, int result_col_index, int source_col_index)

• RyeStatement.mergeRS(int operation, int result_col_index, int source_col_index, int collation)

  operation: SUM, MIN, MAX

• RyeStatement.megeRs(int operation, int resultcol_index, int[] source_col_index)
  oeration: AVG

  source_col_index[0] : index of sum() result column
  source_col_index[1] : index of count() result column

• value types
  SUM: bigint, numeric, double
  MIN, MAX: bigint, numeric, double, datetime, date, time, string

• collation
  How to specify?
  Does driver collation rule have same result with server collation rule?
  https://docs.oracle.com/javase/6/docs/api/java/text/Collator.html

ex)
SELECT COUNT(*) FROM foo;
SELECT SUM(a) FROM foo;
--> RyeStatement.mergeRS(SUM, 1, 1);

SELECT MIN(a) FROM foo;
--> RyeStatement.mergeRs(MIN, 1, 1);
--> RyeStatement.mergeRs(MIN, 1, 1, collation);

SELECT SUM(a), COUNT(a) FROM foo;
--> RyeStatement.mergeRs(AVG, 1, {1,2})

merge order-by query results

step 1

specify sorting rule by API

• RyeStatement.sortRs(SORT_SPEC[] spec_arr, int limit_offset, int limit_count)
  SORT_SPEC:
  int column_index'
  boolean isASCorder;
  int collation;

ex)
SELECT int_col, str_col, other_cols from foo ORDER by 1, 2 DESC limit 5
-->
sort_spec[0] = new SORT_SPEC(1, true, 0);
sort_spec[1] = new SORT_SPEC(2, false, collation);
RyeStatement.sortRS(sort_spec, 0, 5);

step 2

Driver itself set the merging or sorting API using server's parsing result.

connection property: merge_resultset=yes|no

• merge_resultset=no : do not merge results
• merge_resultset=yes : merge results. error if driver cannot convert parsing result to merging or sorting API

prepare result protocol changes