When a new node is added to a write pipeline during flush/sync, if the partial block transfer fails, the write will fail permanently without retrying or continuing with whatever is in the pipeline.
The transfer often fails in busy clusters due to timeout. There is no per-packet ACK between client and datanode or between source and target datanodes. If the total transfer time exceeds the configured timeout + 10 seconds (2 * 5 seconds slack), it is considered failed. Naturally, the failure rate is higher with bigger block sizes.
I propose following changes:
- Transfer timeout needs to be different from per-packet timeout.
- transfer should be retried if fails.