initialize client woff with server.master_repl_offset

[soloestoy]

Initialize client woff with server.master_repl_offset, in case 0 write offset.

BTW, now woff is only used in wait command, and it seems that server.master_repl_offset is enough here, will it be useful in the future?

[antirez]

@soloestoy thank you very much, please could you provide a bit more background about this change, especially when you say "0 write offset"? If the connection was just created, I assume we are always happy to return ASAP from WAIT.

About the other question about woff, yes it is only used by WAIT, but we need to remember what was the value of the master replication offset at the moment we executed the last write command in that client (even if currently we store there the offset of any command, actually, even if it was a read-only one).

So for instance, we execute a command when the offset was 100

We wait some time, then call WAIT in that connection.

Now the acknowledged offset is 110, so we can immediately continue.

Another client however executed the command when the offset was 130, so WAIT should block instead.

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