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From Sebastiano Vigna <vi...@di.unimi.it>
Subject Re: Incredibly slow gzip downloads
Date Sat, 15 Feb 2014 16:06:50 GMT
On 15 Feb 2014, at 12:47 PM, Oleg Kalnichevski <olegk@apache.org> wrote:

> The problem mostly likely has been introduced by HTTPCLIENT-1432 [1]. I
> reviewed the patch once more and could not find anything obviously wrong
> with it. Try reverting the changes introduced by HTTPCLIENT-1432 and see

Subclassing InputStream without overriding the multi-byte read() method is a recipe for disaster...
the inherited method does a byte-by-byte read. You can see what's happening in this hprof
trace:

        java.util.zip.Inflater.inflateBytes(Inflater.java:Unknown line)
        java.util.zip.Inflater.inflate(Inflater.java:259)
        java.util.zip.InflaterInputStream.read(InflaterInputStream.java:152)
        java.util.zip.GZIPInputStream.read(GZIPInputStream.java:116)
        java.util.zip.InflaterInputStream.read(InflaterInputStream.java:122)
        org.apache.http.client.entity.LazyDecompressingInputStream.read(LazyDecompressingInputStream.java:56)
        java.io.InputStream.read(InputStream.java:179)
        it.unimi.di.law.warc.util.InspectableCachedHttpEntity.copyContent(InspectableCachedHttpEntity.java:67)

copyContent() would love to read(byte[],int,int) in a buffer, but since LazyDecompressingInputStream
doesn't override it it invokes instead the read-byte-by-byte inherited method in InputStream,
which in turn now calls for each byte the one-byte read() method from LazyDecompressingInputStream,
which invokes the one-byte read method from InflaterInputStream, which does a multi-byte,
length-one read from GZIPInputStream, which unleashes a similar call on InflaterInputStream,
which unfortunately makes a similar read using the native inflateBytes() method. 

The result is a 10-50x decrease in speed, but I think that a trivial override of read(byte[],int,int)
in LazyDecompressingInputStream will solve the problem.

Ciao,

					seba


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