AHeise commented on a change in pull request #10358: [FLINK-14346]
[serialization] faster implementation of StringValue writeString and readString
URL: https://github.com/apache/flink/pull/10358#discussion_r353348839
##########
File path: flink-core/src/main/java/org/apache/flink/types/StringValue.java
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@@ -759,56 +761,142 @@ public static String readString(DataInput in) throws
IOException {
}
len |= curr << shift;
}
-
+
// subtract one for the null length
len -= 1;
-
- final char[] data = new char[len];
- for (int i = 0; i < len; i++) {
- int c = in.readUnsignedByte();
- if (c < HIGH_BIT) {
- data[i] = (char) c;
- } else {
+ /* as we have no idea about byte-length of the serialized
string, we cannot fully
+ * read it into memory buffer. But we can do it in an
optimistic way:
+ * 1. In a happy case when the string is an us-ascii one, then
byte_len == char_len
+ * 2. If we spot at least one character with code >= 127, then
we reallocate the buffer
+ * to accommodate for the next characters.
+ */
+
+ // happily assume that the string is an 7 bit us-ascii one
+ byte[] buf = new byte[len];
+ in.readFully(buf);
+
+ final char[] data = new char[len];
+ int charPosition = 0;
+ int bufSize = len;
+ int bytePosition = 0;
+
+ while (charPosition < len) {
+ // there is at least `char count - char position` bytes
left in case if all the
+ // remaining characters are 7 bit.
+ int remainingBytesEstimation = len - charPosition;
+ int c;
+ if (bytePosition == bufSize) {
+ // need to expand the buffer as we are already
reached the end.
+ // we also reuse the old buffer, as it's
capacity must be enough in any case.
Review comment:
the comment is a bit misleading. If we have 8 Cyrillic letters, we would
first read 4 letters, then 2, then 1, then the last one each using the
following line. When I read the comment first, I thought we would read 4
letters and then again 4 letters. I'd change it into `// we also reuse the old
buffer, as it's capacity must always be > remainingBytesEstimation`.
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