when set mem-queue-size=0, maybe lost a message.

[syz521]

[syz521]

when get first message from memoryMsgChan and still if nsqd crash , it will lost

[ploxiln]

Correct, mem-queue-size=0 is not a 100% guarantee, and is not generally recommended because most of nsqd was not designed for that mode of operation, so it has some weird edge-cases and inefficiencies.

See also:

• nsqd: per-topic WAL #625
• nsqd: deferred messages not deferred with --mem-queue-size=0 #1375

[ploxiln]

see also #1386