Bookie GC pressure when use ReadEntryProcessorV3

[horizonzy]

BUG REPORT When we get entry from bookie in ReadEntryProcessorV3#readEntry, the response is DirectByteBuf, the v3 use proto buf response. So it will copy byte array to proto buf builder, it will use heap memory.

If the user read request is frequent, it will introduce gc pressure.

https://github.com/apache/bookkeeper/blob/ca7d7c23e3aa572befeb447157b3ef9d96bb1449/bookkeeper-server/src/main/java/org/apache/bookkeeper/proto/ReadEntryProcessorV3.java#L179

    public static ByteString copyFrom(ByteBuffer bytes, int size) {
        checkRange(0, size, bytes.remaining());
        byte[] copy = new byte[size];
        bytes.get(copy);
        return new LiteralByteString(copy);
    }

[dlg99]

there are a lot of places like that for v3 requests (grep for ByteString.copyFrom). As I understand. that at leas a part of the reason for Pulsar to use v2 protocol https://github.com/apache/pulsar/blob/89b6a535aa8de8e2475cd39320897700e64d269e/conf/broker.conf#L870

You can try using UnsafeByteOperations.unsafeWrap instead of ByteString.copyFrom (e.g. see https://github.com/apache/bookkeeper/pull/1361 ) to reduce memory pressure but you have to be really careful about not recycling entryBody (and similar) before the protobuf-related operation completes.