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[SPARK-22498][SQL] Fix 64KB JVM bytecode limit problem with concat #19728

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[SPARK-22498][SQL] Fix 64KB JVM bytecode limit problem with concat #19728

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bc97d41
initial commit
kiszk Nov 12, 2017
0ed8d16
address review comment
kiszk Nov 13, 2017
366f721
support elt
kiszk Nov 13, 2017
6fdb451
address review comment
kiszk Nov 13, 2017
e6b73ab
address review comment
kiszk Nov 13, 2017
cd20410
address review comment
kiszk Nov 13, 2017
e668b98
address review comment
kiszk Nov 13, 2017
555575e
address review comment
kiszk Nov 16, 2017
22019b1
address review comments
kiszk Nov 17, 2017
b9ca4ff
drop changes for concat_ws and elt
kiszk Nov 18, 2017
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75 changes: 55 additions & 20 deletions ...catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/stringExpressions.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -63,15 +63,28 @@ case class Concat(children: Seq[Expression]) extends Expression with ImplicitCas

override protected def doGenCode(ctx: CodegenContext, ev: ExprCode): ExprCode = {
val evals = children.map(_.genCode(ctx))
val inputs = evals.map { eval =>
s"${eval.isNull} ? null : ${eval.value}"
}.mkString(", ")
ev.copy(evals.map(_.code).mkString("\n") + s"""
boolean ${ev.isNull} = false;
UTF8String ${ev.value} = UTF8String.concat($inputs);
if (${ev.value} == null) {
${ev.isNull} = true;
val argNums = evals.length
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nit: numArgs.

val args = ctx.freshName("argLen")
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argLen? I think it's not length of args?

ctx.addMutableState("UTF8String[]", args, "")
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I think we can avoid defining this as a global variable, what do you think?


val inputs = evals.zipWithIndex.map { case (eval, index) =>
if (eval.isNull != "true") {
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If eval.isNull is not a pre-evaluated constant?

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If eval.isNull is not a pre-evaluated constant, I expect that the following code at lines 73-74 will be generated. Only when we ensure it is true, we can avoid assigning a value (use default null value).

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please do not mix in optimizations with bug fix

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I see. I will remove this.

s"""
${eval.code}
if (!${eval.isNull}) {
$args[$index] = ${eval.value};
}
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I think we are better to assign null too if eval.isNull == null, because args is global variable and we need to override all values for previous row.

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Thanks, while args is global, UTF8String[] is allocated before executing these assignments. Thus, we can ensure all of elements in args are null.
What do you think?

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That is guaranteed before the first row processed. After we process rows, args are updated for each row. E.g., args[0] can be updated and assigned with a string for row 0. In next row, if eval.isNull is evaluated to true, we don't override back to null, so arg[0] is still the string value for row 0.

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@kiszk kiszk Nov 13, 2017 •
edited
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When the next row is processed, $args = new UTF8String[$argNums] is executed again in apply() method. In other words, I think that current implementation does not reuse UTF8String[] between different rows.
Do you mean UTF8String[] is reused between different rows?

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Oh, I see. I didn't notice that args is not globally initialized.

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Thank you for taking your time for my code.
It is not easy to imagine the generated code. I may have to put the generated code.

"""
} else {
""
}
}
val codes = ctx.splitExpressions(ctx.INPUT_ROW, inputs)
ev.copy(s"""
$args = new UTF8String[$argNums];
$codes
UTF8String ${ev.value} = UTF8String.concat($args);
boolean ${ev.isNull} = ${ev.value} == null;
""")
}
}
Expand Down Expand Up @@ -126,18 +139,36 @@ case class ConcatWs(children: Seq[Expression])
// All children are strings. In that case we can construct a fixed size array.
val evals = children.map(_.genCode(ctx))

val inputs = evals.map { eval =>
s"${eval.isNull} ? (UTF8String) null : ${eval.value}"
}.mkString(", ")

ev.copy(evals.map(_.code).mkString("\n") + s"""
UTF8String ${ev.value} = UTF8String.concatWs($inputs);
val argNums = evals.length
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this should be evals.length -1, or even better, I'd suggest to declare two variables: sep and strings (or the name you prefer) to hold head and tail. This would help readability too IMHO.

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I am sorry that I cannot understand your suggestion.
argNums is referred as $argNums to allocate an array. Are you suggesting to allocate an array as new UTF8String[$argNums + 1]?

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no, I am saying the opposite. Let's consider an example, maybe I better can explain what I mean in this way. Let's assume that we are running concat_ws(',', 'a', 'b'). Then, evals would contain 3 elements. So here your argNums would be 3. But here you would be using only $args[0] and $args[1], because the first element (',', the separator) is handled differently.
Thus, I would suggest to have something like:

val sep = evals.head
val strings = evals.tail
val argNums = strings.length // note that this is evals.length -1
...

I think that in this way the code would be much clearer (other than fixing this little bug).

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Thank you for your kindly explanation. I totally agree with you.

val args = ctx.freshName("argLen")
ctx.addMutableState("UTF8String[]", args, "")
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this also can be kept method local, IMHO


val inputs = evals.tail.zipWithIndex.map { case (eval, index) =>
if (eval.isNull != "true") {
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Same issue as https://github.com/apache/spark/pull/19728/files#r150441287.

s"""
${eval.code}
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nit: in this and the next 4 lines an indentation space is missing if I am not wrong.

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good catch

if (!${eval.isNull}) {
$args[$index] = ${eval.value};
}
"""
} else {
""
}
}
val codes = s"${evals.head.code}\n" + ctx.splitExpressions(ctx.INPUT_ROW, inputs)
ev.copy(s"""
$args = new UTF8String[$argNums];
$codes
UTF8String ${ev.value} = UTF8String.concatWs(${evals.head.value}, $args);
boolean ${ev.isNull} = ${ev.value} == null;
""")
} else {
val array = ctx.freshName("array")
ctx.addMutableState("UTF8String[]", array, "")
val varargNum = ctx.freshName("varargNum")
ctx.addMutableState("int", varargNum, "")
val idxInVararg = ctx.freshName("idxInVararg")
ctx.addMutableState("int", idxInVararg, "")

val evals = children.map(_.genCode(ctx))
val (varargCount, varargBuild) = children.tail.zip(evals.tail).map { case (child, eval) =>
Expand All @@ -163,13 +194,17 @@ case class ConcatWs(children: Seq[Expression])
}
}.unzip

ev.copy(evals.map(_.code).mkString("\n") +
val codes = ctx.splitExpressions(ctx.INPUT_ROW, evals.map(_.code))
val varargCounts = ctx.splitExpressions(ctx.INPUT_ROW, varargCount)
val varargBuilds = ctx.splitExpressions(ctx.INPUT_ROW, varargBuild)
ev.copy(
s"""
int $varargNum = ${children.count(_.dataType == StringType) - 1};
int $idxInVararg = 0;
${varargCount.mkString("\n")}
UTF8String[] $array = new UTF8String[$varargNum];
${varargBuild.mkString("\n")}
$codes
$varargNum = ${children.count(_.dataType == StringType) - 1};
$idxInVararg = 0;
$varargCounts
$array = new UTF8String[$varargNum];
$varargBuilds
UTF8String ${ev.value} = UTF8String.concatWs(${evals.head.value}, $array);
boolean ${ev.isNull} = ${ev.value} == null;
""")
Expand Down
19 changes: 19 additions & 0 deletions ...yst/src/test/scala/org/apache/spark/sql/catalyst/expressions/StringExpressionsSuite.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,12 @@ class StringExpressionsSuite extends SparkFunSuite with ExpressionEvalHelper {
// scalastyle:on
}

test("SPARK-22498: Concat should not generate codes beyond 64KB") {
val N = 5000
val strs = (1 to N).map(x => s"x_$x")
checkEvaluation(Concat(strs.map(Literal.create(_, StringType))), strs.mkString, EmptyRow)
}

test("concat_ws") {
def testConcatWs(expected: String, sep: String, inputs: Any*): Unit = {
val inputExprs = inputs.map {
Expand Down Expand Up @@ -74,6 +80,19 @@ class StringExpressionsSuite extends SparkFunSuite with ExpressionEvalHelper {
// scalastyle:on
}

test("SPARK-22498: ConcatWs should not generate codes beyond 64KB") {
val N = 5000
val sepExpr = Literal.create("#", StringType)
val strings1 = (1 to N).map(x => s"s$x")
val inputsExpr1 = strings1.map(Literal.create(_, StringType))
checkEvaluation(ConcatWs(sepExpr +: inputsExpr1), strings1.mkString("#"), EmptyRow)

val strings2 = (1 to N).map(x => Seq(s"s$x"))
val inputsExpr2 = strings2.map(Literal.create(_, ArrayType(StringType)))
checkEvaluation(
ConcatWs(sepExpr +: inputsExpr2), strings2.map(s => s(0)).mkString("#"), EmptyRow)
}

test("elt") {
def testElt(result: String, n: java.lang.Integer, args: String*): Unit = {
checkEvaluation(
Expand Down