[FLINK-1093] Add non-multiplexing NetworkConnectionManager

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Not A Problem
• Affects Version/s: 0.7.0-incubating
• Component/s: Runtime / Coordination
• Assignee: Unassigned
• Reporter: Ufuk Celebi
• Created: 07/Sep/14 10:49
• Updated: 02/Feb/15 17:10
• Resolved: 02/Feb/15 17:10

Description

When translating a JobGraph to an ExecutionGraph, edges are assigned connection indexes to ensure deadlock freedom of the network stack. Deadlocks can easily occur when multiplexing multiple logical channels over a single TCP connection, because of the limited network buffers. Each incoming envelope, which has an attached buffer, needs to request a network buffer from the receiver's input buffer pool. If the receiver does not have a buffer available, it unsubscribes from the TCP connection until a new buffer is available. This unsubscribe then affects all other logical channels, which are multiplexed over the same TCP connection. With certain user programs this can result in a deadlock.

One of the problems when running in multiplexed mode is the question of when to close TCP connections in a reliable way without loosing or re-ordering network envelopes (as evident in FLINK-1063). In non-multiplexed mode this is trivial, because every logical channel is mapped to a phyiscal channel and the close of the logical channel translates to a close of the physical channel.

However, this approach results in limited scalability as high degrees of parallelism result in a high number of TCP connections per machine, which are continuously opened and closed. Still, it is useful as a baseline and should work fine with smaller setups.

Issue Links

• is related to: FLINK-1063 Race condition in NettyConnectionManager
• is superceded by: FLINK-986 Add intermediate results to distributed runtime