Github user koeninger commented on a diff in the pull request:
https://github.com/apache/spark/pull/14502#discussion_r73713830
--- 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 --
What I'm saying is that, at least at the time, the mysql driver ignored the
actual number set there, unless it was min value. It only used it to
toggle between "stream results" and "fetch all results", with nothing in
between.
On Fri, Aug 5, 2016 at 10:14 AM, Sean Owen <[email protected]> wrote:
> In core/src/main/scala/org/apache/spark/rdd/JdbcRDD.scala
> <https://github.com/apache/spark/pull/14502#discussion_r73708585>:
>
> > stmt.setFetchSize(Integer.MIN_VALUE)
> > logInfo("statement fetch size set to: " + stmt.getFetchSize + "
to force MySQL streaming ")
> > + } else if (url.matches("jdbc:postgresql:*")) {
>
> 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.
>
> â
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