rednaxelafx commented on a change in pull request #23406: [SPARK-26504][SQL]
Rope-wise dumping of Spark plans
URL: https://github.com/apache/spark/pull/23406#discussion_r244550383
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/StringUtils.scala
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@@ -87,4 +89,34 @@ object StringUtils {
}
funcNames.toSeq
}
+
+ /**
+ * Concatenation of sequence of strings to final string with cheap append
method
+ * and one memory allocation for the final string.
+ */
+ class StringConcat {
+ private val strings = new ArrayBuffer[String]
+ private var length: Int = 0
+
+ /**
+ * Appends a string and accumulates its length to allocate a string buffer
for all
+ * appended strings once in the toString method.
+ */
+ def append(s: String): Unit = {
+ if (s != null) {
+ strings.append(s)
+ length += s.length
+ }
+ }
+
+ /**
+ * The method allocates memory for all appended strings, writes them to
the memory and
+ * returns concatenated string.
+ */
+ override def toString: String = {
+ val result = new StringBuffer(length)
Review comment:
Can we just use `java.lang.StringBuilder` here for the sake of reducing one
useless allocation of the Scala wrapper?
Which `StringBuffer` is this anyway? If you're using the Scala
scala.collection.mutable.*, it should have been `StringBuilder`, right?
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