TWEAK: do not set global log level in NewBinlogSyncer

[taylorchu]

This reverts 0baad4d.

Setting a global log level in an initializer causes unwanted side effects in many cases. User who needs this should do log.SetLevelByString in main program only.

[taylorchu]

@siddontang @b13f

[taylorchu]

Another option will be having an user-provided logger. Since go community does not currently have a consensus on logger interface, this might not be wanted.

[siddontang]

Hi @taylorchu

I remember that some users meet the log info problem, so they want to control through configuration.

Maybe we can try:

if cfg.LogLevel != "" { log.SetLevelByString(cfg.LogLevel) }

So if the user set a log level config, he/she can use it.

[taylorchu]

If that is the problem, then setting log level there is not a good solution. Imagine that you create NewBinlogSyncer with "info" and "error" log level. You will expect that one syncer has log level of info, and the other has log level of error. However, the code we have now will only honor the BinlogSyncer of the latter call.

This gets worse if you use NewBinlogSyncer with goroutines. The logger is not only a global state, but that state is controlled by a nondeterministic function call order.

[siddontang]

Yes @taylorchu

IMO, I don't like go-mysql contains any log. But the missing log is hard for us to locate problems sometimes. Maybe a log interface is better, but Go doesn't supply a standard way sadly.

What is your opinion?

[taylorchu]

type StdLogger interface { Print(...interface{}) Printf(string, ...interface{}) } 

Many go logger libraries support this interface, and that includes ngaut/log and logrus.

By default the package's logger uses stdlib logger, and it should be settable.

[siddontang]

Good idea, but I want to use different log level, maybe I can define a log interface like https://github.com/grpc/grpc-go/blob/master/grpclog/loggerv2.go#L30.

If the user doesn't pass a logger to go-mysql, we will use a NoopLogger which does nothing by default.

[taylorchu]

Is there a use case to have different log level within this package github.com/siddontang/go-mysql?

For our usage, we really don't care. Every log line here is equivalent to "DEBUG" level.

[siddontang]

maybe needed. I will merge this PR now, thanks, @taylorchu.

Maybe it is better to support passing a Logger, I will do it later.