[SPARK-14267] [SQL] [PYSPARK] execute multiple Python UDFs within single batch

## What changes were proposed in this pull request?

This PR support multiple Python UDFs within single batch, also improve the performance.

```python
>>> from pyspark.sql.types import IntegerType
>>> sqlContext.registerFunction("double", lambda x: x * 2, IntegerType())
>>> sqlContext.registerFunction("add", lambda x, y: x + y, IntegerType())
>>> sqlContext.sql("SELECT double(add(1, 2)), add(double(2), 1)").explain(True)
== Parsed Logical Plan ==
'Project [unresolvedalias('double('add(1, 2)), None),unresolvedalias('add('double(2), 1), None)]
+- OneRowRelation$

== Analyzed Logical Plan ==
double(add(1, 2)): int, add(double(2), 1): int
Project [double(add(1, 2))#14,add(double(2), 1)#15]
+- Project [double(add(1, 2))#14,add(double(2), 1)#15]
   +- Project [pythonUDF0#16 AS double(add(1, 2))#14,pythonUDF0#18 AS add(double(2), 1)#15]
      +- EvaluatePython [add(pythonUDF1#17, 1)], [pythonUDF0#18]
         +- EvaluatePython [double(add(1, 2)),double(2)], [pythonUDF0#16,pythonUDF1#17]
            +- OneRowRelation$

== Optimized Logical Plan ==
Project [pythonUDF0#16 AS double(add(1, 2))#14,pythonUDF0#18 AS add(double(2), 1)#15]
+- EvaluatePython [add(pythonUDF1#17, 1)], [pythonUDF0#18]
   +- EvaluatePython [double(add(1, 2)),double(2)], [pythonUDF0#16,pythonUDF1#17]
      +- OneRowRelation$

== Physical Plan ==
WholeStageCodegen
:  +- Project [pythonUDF0#16 AS double(add(1, 2))#14,pythonUDF0#18 AS add(double(2), 1)#15]
:     +- INPUT
+- !BatchPythonEvaluation [add(pythonUDF1#17, 1)], [pythonUDF0#16,pythonUDF1#17,pythonUDF0#18]
   +- !BatchPythonEvaluation [double(add(1, 2)),double(2)], [pythonUDF0#16,pythonUDF1#17]
      +- Scan OneRowRelation[]
```

## How was this patch tested?

Added new tests.

Using the following script to benchmark 1, 2 and 3 udfs,
```
df = sqlContext.range(1, 1 << 23, 1, 4)
double = F.udf(lambda x: x * 2, LongType())
print df.select(double(df.id)).count()
print df.select(double(df.id), double(df.id + 1)).count()
print df.select(double(df.id), double(df.id + 1), double(df.id + 2)).count()
```
Here is the results:

N | Before | After  | speed up
---- |------------ | -------------|------
1 | 22 s | 7 s |  3.1X
2 | 38 s | 13 s | 2.9X
3 | 58 s | 16 s | 3.6X

This benchmark ran locally with 4 CPUs. For 3 UDFs, it launched 12 Python before before this patch, 4 process after this patch. After this patch, it will use less memory for multiple UDFs than before (less buffering).

Author: Davies Liu <davies@databricks.com>

Closes #12057 from davies/multi_udfs.

1 files changed, 52 insertions, 16 deletions

diff --git a/python/pyspark/worker.py b/python/pyspark/worker.py
index 0f05fe31aa..cf47ab8f96 100644
--- a/python/pyspark/worker.py
+++ b/python/pyspark/worker.py
@@ -29,7 +29,7 @@ from pyspark.accumulators import _accumulatorRegistry
 from pyspark.broadcast import Broadcast, _broadcastRegistry
 from pyspark.files import SparkFiles
 from pyspark.serializers import write_with_length, write_int, read_long, \
-    write_long, read_int, SpecialLengths, UTF8Deserializer, PickleSerializer
+    write_long, read_int, SpecialLengths, UTF8Deserializer, PickleSerializer, BatchedSerializer
 from pyspark import shuffle
 
 pickleSer = PickleSerializer()
@@ -59,7 +59,54 @@ def read_command(serializer, file):
 
 def chain(f, g):
     """chain two function together """
-    return lambda x: g(f(x))
+    return lambda *a: g(f(*a))
+
+
+def wrap_udf(f, return_type):
+    if return_type.needConversion():
+        toInternal = return_type.toInternal
+        return lambda *a: toInternal(f(*a))
+    else:
+        return lambda *a: f(*a)
+
+
+def read_single_udf(pickleSer, infile):
+    num_arg = read_int(infile)
+    arg_offsets = [read_int(infile) for i in range(num_arg)]
+    row_func = None
+    for i in range(read_int(infile)):
+        f, return_type = read_command(pickleSer, infile)
+        if row_func is None:
+            row_func = f
+        else:
+            row_func = chain(row_func, f)
+    # the last returnType will be the return type of UDF
+    return arg_offsets, wrap_udf(row_func, return_type)
+
+
+def read_udfs(pickleSer, infile):
+    num_udfs = read_int(infile)
+    if num_udfs == 1:
+        # fast path for single UDF
+        _, udf = read_single_udf(pickleSer, infile)
+        mapper = lambda a: udf(*a)
+    else:
+        udfs = {}
+        call_udf = []
+        for i in range(num_udfs):
+            arg_offsets, udf = read_single_udf(pickleSer, infile)
+            udfs['f%d' % i] = udf
+            args = ["a[%d]" % o for o in arg_offsets]
+            call_udf.append("f%d(%s)" % (i, ", ".join(args)))
+        # Create function like this:
+        #   lambda a: (f0(a0), f1(a1, a2), f2(a3))
+        mapper_str = "lambda a: (%s)" % (", ".join(call_udf))
+        mapper = eval(mapper_str, udfs)
+
+    func = lambda _, it: map(mapper, it)
+    ser = BatchedSerializer(PickleSerializer(), 100)
+    # profiling is not supported for UDF
+    return func, None, ser, ser
 
 
 def main(infile, outfile):
@@ -107,21 +154,10 @@ def main(infile, outfile):
                 _broadcastRegistry.pop(bid)
 
         _accumulatorRegistry.clear()
-        row_based = read_int(infile)
-        num_commands = read_int(infile)
-        if row_based:
-            profiler = None  # profiling is not supported for UDF
-            row_func = None
-            for i in range(num_commands):
-                f, returnType, deserializer = read_command(pickleSer, infile)
-                if row_func is None:
-                    row_func = f
-                else:
-                    row_func = chain(row_func, f)
-            serializer = deserializer
-            func = lambda _, it: map(lambda x: returnType.toInternal(row_func(*x)), it)
+        is_sql_udf = read_int(infile)
+        if is_sql_udf:
+            func, profiler, deserializer, serializer = read_udfs(pickleSer, infile)
         else:
-            assert num_commands == 1
             func, profiler, deserializer, serializer = read_command(pickleSer, infile)
 
         init_time = time.time()