We are using maven for build process automation with docker. This sometimes involves uploading and downloading artifacts with a few gigabytes in size. Here, maven's transfer speed is consistently and reproducibly slow. For instance, an artifact with 7,5 GB in size took almost two hours to transfer in spite of a 100 MB/s connection with respective reproducible download speed from the remote nexus artifact repository when using a browser to download. The same is true when uploding such an artifact.
I have investigated the issue using JProfiler. The result shows an issue in AbstractWagon's transfer( Resource resource, InputStream input, OutputStream output, int requestType, long maxSize ) method used for remote artifacts and the same issue in AbstractHttpClientWagon#writeTo(OutputStream).
Here, the input stream is read in a loop using a 4 Kb buffer. Whenever data is received, the received data is pushed to downstream listeners via fireTransferProgress. These listeners (or rather consumers) perform expensive tasks.
Now, the underlying InputStream implementation used in transfer will return calls to read(buffer, offset, length) as soon as some data is available. That is, fireTransferProgress may well be invoked with an average number of bytes less than half the buffer capacity (this varies with the underlying network and hardware architecture). Consequently, fireTransferProgress is invoked millions of times for large files. As this is a blocking operation, the time spent in fireTransferProgress dominates and drastically slows down the transfers by at least one order of magnitude.
In our case, we found download speed reduced from a theoretical optimum of ~80 seconds to to more than 3200 seconds.
From an architectural perspective, I would not want to make the consumers / listeners invoked via fireTransferProgress aware of their potential impact on download speed, but rather refactor the transfer method such that it uses a buffer strategy reducing the the number of fireTransferProgress invocations. This should be done with regard to the expected file size of the transfer, such that fireTransferProgress is invoked often enough but not to frequent.