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https://issues.apache.org/jira/browse/SPARK-23347?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16354907#comment-16354907
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Ted Yu commented on SPARK-23347:
--------------------------------
See JDK 1.8 code:
{code}
class DeflaterOutputStream {
public void write(int b) throws IOException {
byte[] buf = new byte[1];
buf[0] = (byte)(b & 0xff);
write(buf, 0, 1);
}
public void write(byte[] b, int off, int len) throws IOException {
if (def.finished()) {
throw new IOException("write beyond end of stream");
}
if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return;
}
if (!def.finished()) {
def.setInput(b, off, len);
while (!def.needsInput()) {
deflate();
}
}
}
}
class GZIPOutputStream extends DeflaterOutputStream {
public synchronized void write(byte[] buf, int off, int len)
throws IOException
{
super.write(buf, off, len);
crc.update(buf, off, len);
}
}
class Deflater {
private native int deflateBytes(long addr, byte[] b, int off, int len, int
flush);
}
class CRC32 {
public void update(byte[] b, int off, int len) {
if (b == null) {
throw new NullPointerException();
}
if (off < 0 || len < 0 || off > b.length - len) {
throw new ArrayIndexOutOfBoundsException();
}
crc = updateBytes(crc, b, off, len);
}
private native static int updateBytes(int crc, byte[] b, int off, int len);
}
{code}
For each data byte, the code above has to allocate 1 single byte array, acquire
several locks, call two native JNI methods (Deflater.deflateBytes and
CRC32.updateBytes).
> Introduce buffer between Java data stream and gzip stream
> ---------------------------------------------------------
>
> Key: SPARK-23347
> URL: https://issues.apache.org/jira/browse/SPARK-23347
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core
> Affects Versions: 2.2.0
> Reporter: Ted Yu
> Priority: Minor
>
> Currently GZIPOutputStream is used directly around ByteArrayOutputStream
> e.g. from KVStoreSerializer :
> {code}
> ByteArrayOutputStream bytes = new ByteArrayOutputStream();
> GZIPOutputStream out = new GZIPOutputStream(bytes);
> {code}
> This seems inefficient.
> GZIPOutputStream does not implement the write(byte) method. It only provides
> a write(byte[], offset, len) method, which calls the corresponding JNI zlib
> function.
> BufferedOutputStream can be introduced wrapping GZIPOutputStream for better
> performance.
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