diff --git a/docs/programming-guide.md b/docs/programming-guide.md
index 0b24a8b88b..65d75b85ef 100644
--- a/docs/programming-guide.md
+++ b/docs/programming-guide.md
@@ -899,7 +899,7 @@ for details.
reduceByKey(func, [numTasks]) |
- When called on a dataset of (K, V) pairs, returns a dataset of (K, V) pairs where the values for each key are aggregated using the given reduce function. Like in groupByKey , the number of reduce tasks is configurable through an optional second argument. |
+ When called on a dataset of (K, V) pairs, returns a dataset of (K, V) pairs where the values for each key are aggregated using the given reduce function func, which must be of type (V,V) => V. Like in groupByKey , the number of reduce tasks is configurable through an optional second argument. |
aggregateByKey(zeroValue)(seqOp, combOp, [numTasks]) |
@@ -1067,7 +1067,10 @@ storage levels is:
Store RDD in serialized format in Tachyon.
Compared to MEMORY_ONLY_SER, OFF_HEAP reduces garbage collection overhead and allows executors
to be smaller and to share a pool of memory, making it attractive in environments with
- large heaps or multiple concurrent applications.
+ large heaps or multiple concurrent applications. Furthermore, as the RDDs reside in Tachyon,
+ the crash of an executor does not lead to losing the in-memory cache. In this mode, the memory
+ in Tachyon is discardable. Thus, Tachyon does not attempt to reconstruct a block that it evicts
+ from memory.
|