Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/14502#discussion_r73708585
--- Diff: core/src/main/scala/org/apache/spark/rdd/JdbcRDD.scala ---
@@ -79,12 +79,18 @@ class JdbcRDD[T: ClassTag](
val conn = getConnection()
val stmt = conn.prepareStatement(sql, ResultSet.TYPE_FORWARD_ONLY,
ResultSet.CONCUR_READ_ONLY)
- // setFetchSize(Integer.MIN_VALUE) is a mysql driver specific way to
force streaming results,
- // rather than pulling entire resultset into memory.
- // see
http://dev.mysql.com/doc/refman/5.0/en/connector-j-reference-implementation-notes.html
- if (conn.getMetaData.getURL.matches("jdbc:mysql:.*")) {
+ val url = conn.getMetaData.getURL
+ if (url.matches("jdbc:mysql:.*")) {
+ // setFetchSize(Integer.MIN_VALUE) is a mysql driver specific way to
force streaming results,
+ // rather than pulling entire resultset into memory.
+ // see
http://dev.mysql.com/doc/refman/5.0/en/connector-j-reference-implementation-notes.html
+
stmt.setFetchSize(Integer.MIN_VALUE)
logInfo("statement fetch size set to: " + stmt.getFetchSize + " to
force MySQL streaming ")
+ } else if (url.matches("jdbc:postgresql:*")) {
--- End diff --
Yeah that's why the fetch size shouldn't be effectively infinite, but I
think this mode means fetch one at a time, which is the other extreme. What if
this were, say, fetching 100 records at once? if that strikes you as OK, maybe
that's better for efficiency.
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