Hi all, https://github.com/apache/pulsar/pull/14453 <https://github.com/apache/pulsar/pull/14453> please take a look.
Thanks, Tao Jiuming > 2022年2月24日 上午1:05，Jiuming Tao <jm...@streamnative.io> 写道： > > Hi all, >> >> 2. When there are hundreds MB metrics data collected, it causes high heap >> memory usage, high CPU usage and GC pressure. In the >> `PrometheusMetricsGenerator#generate` method, it uses >> `ByteBufAllocator.DEFAULT.heapBuffer()` to allocate memory for writing >> metrics data. The default size of `ByteBufAllocator.DEFAULT.heapBuffer()` is >> 256 bytes, when the buffer resizes, the new buffer capacity is 512 >> bytes(power of 2) and with `mem_copy` operation. >> If I want to write 100 MB data to the buffer, the current buffer size is 128 >> MB, and the total memory usage is close to 256 MB (256bytes + 512 bytes + 1k >> + .... + 64MB + 128MB). When the buffer size is greater than netty buffer >> chunkSize(16 MB), it will be allocated as UnpooledHeapByteBuf in the heap. >> After writing metrics data into the buffer, return it to the client by >> jetty, jetty will copy it into jetty's buffer with memory allocation in the >> heap, again! >> In this condition, for the purpose of saving memory, avoid high CPU >> usage(too much memory allocations and `mem_copy` operations) and reducing GC >> pressure, I want to change `ByteBufAllocator.DEFAULT.heapBuffer()` to >> `ByteBufAllocator.DEFAULT.compositeDirectBuffer()`, it wouldn't cause >> `mem_copy` operations and huge memory allocations(CompositeDirectByteBuf is >> a bit slowly in read/write, but it's worth). After writing data, I will call >> the `HttpOutput#write(ByteBuffer)` method and write it to the client, the >> method won't cause `mem_copy` (I have to wrap ByteBuf to ByteBuffer, if >> ByteBuf wrapped, there will be zero-copy). > > The jdk in my local is jdk15, I just noticed that in jdk8, ByteBuffer cannot > be extended and implemented. So, if allowed, I will write metrics data to > temp files and send it to client by jetty’s send_file. It will be turned out > a better performance than `CompositeByteBuf`, and takes lower CPU usage due > to I/O blocking.(The /metrics endpoint will be a bit slowly, I believe it’s > worth). > If not allowed, it’s no matter and it also has a better performance than > `ByteBufAllocator.DEFAULT.heapBuffer()`(see the first image in original > mail). > > Thanks, > Tao Jiuming
