Github user selvaganesang commented on a diff in the pull request:
https://github.com/apache/trafodion/pull/1694#discussion_r243471406
--- Diff:
core/conn/jdbcT4/src/main/java/org/trafodion/jdbc/t4/TrafT4ResultSet.java ---
@@ -2779,6 +2779,19 @@ public boolean next() throws SQLException {
maxRowCnt = maxRows - totalRowsFetched_;
}
+ // if (row width) * (fetch rows) too large, there will have core
in server side.
+ // once fetch bytes bigger than 1GB, devide several times to fetch,
+ // each time fetch bytes less than 1GB.
+ if (outputDesc_ != null && outputDesc_[0] != null) {
+ long rowLength = outputDesc_[0].rowLength_;
+ long oneGB = 1024 * 1024 * 1024;
+ if (rowLength * maxRowCnt >= oneGB) {
+ double multi = (rowLength * maxRowCnt) / (double)oneGB;
+ multi = Math.ceil(multi); // devide several times to fetch
+ maxRowCnt = (int) (maxRowCnt / multi);
+ }
+ }
+
--- End diff --
Just spent some time looking at this change. As per JDBC specification,
Statement.setMaxRows sets the upper limit on the number of rows in the result
set. Statement.setFetchSize sets the hint for the driver to fetch how many rows
are fetched in next(). maxRows_ and fetchSize_ in this method corresponds to
these values respectively. It is possible that the application doesn't set
this value at all. Any case, JDBC driver can decide the fetchSize based on the
hint or its limitations. I would suggest the following:
1. Move this logic to calculate the number of rows to getFetchSize
2. Use a data source property to get the fetch size in terms of MB rather
than assuming 1GB in calculation. Assume a default value a far less than 1GB
says 50 or 100 MB if the property is not set.
3. Calculate the number of rows fetchSize_ based on the setFetchSize and
this property value which ever doesn't exceed the size in terms of MB.
4. Use getFetchSize() in this method to get the fetchSize_
This would ensure that Trafodion conforms to JDBC specification in a better
way because it would let the application know how the hint of setFetchSize
works.
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