Major Description
From the user mailing list:
I'm running into a "java.lang.IllegalStateException: iterator() can only be called once on this Iterable" [1] when running a unit test that
utilizes a MemCollection. The pipeline appears to runs fine when running on a cluster. I have a PGroupedTable that I am running multiple operations (mapValues, ungroup) [2] on that is causing the exception. The mapValues and the ungroup operations are run in separate jobs on the cluster, so I don't believe I should be running into iterator issues. This constraint was introduced by CRUNCH-192 [3].
Gabriel Reid stated "Looks like the MemPipeline is doing something wrong when multiple PCollections are created from a single PCollection." [4]
[1]
apache-crunch-0.8.4 branch
iterator() can only be called once on this Iterable
java.lang.IllegalStateException: iterator() can only be called once on this Iterable
at org.apache.crunch.impl.SingleUseIterable.iterator(SingleUseIterable.java:43)
at org.apache.crunch.impl.mem.collect.MemGroupedTable$UngroupFn.process(MemGroupedTable.java:148)
at org.apache.crunch.impl.mem.collect.MemGroupedTable$UngroupFn.process(MemGroupedTable.java:145)
at org.apache.crunch.impl.mem.collect.MemCollection.parallelDo(MemCollection.java:155)
at org.apache.crunch.impl.mem.collect.MemCollection.parallelDo(MemCollection.java:143)
at org.apache.crunch.impl.mem.collect.MemGroupedTable.ungroup(MemGroupedTable.java:142)
[2]
PGroupedTable<String, Item> itemsByPersonId =
AvroCollections.keyByAvroField(items, "person_id", Avros.strings()).groupByKey();
PTable<String, Long> newestOrderByPersonId =
itemsByPersonId
.mapValues("Find latest order for each person", new MaxOrderMapFn(), Avros.longs());
return itemsByPersonId.ungroup().join(newestOrderByPersonId).parallelDo(
"Filter old items, leaving only current order items",
new PreviousOrderItemFilter(),
Avros.tableOf(Avros.strings(), Avros.specifics(Item.class)));
[3] https://issues.apache.org/jira/browse/CRUNCH-192
https://github.com/apache/crunch/commit/cbc7c2fb30ad0486e7ec60656c079c81e41eda2c
[4] http://mail-archives.apache.org/mod_mbox/crunch-user/201604.mbox/date