Support GC

[ekexium]

TiKV uses MVCC to support transactions, thus GC is needed to remove stale data.
Current implementation of rust-client does not provide GC functionalities.

A workaround is using the script which calls TiDB's GC functions to manually trigger GC.

An initial implementation of GC #182 .

If we let users manage GC, we should provide a guide.

[nrc]

I noticed that the gc function does not use the gc request, which is a bit confusing. AIUI, we currently gc locks but not deleted data (the delete ranges step) or old data (which uses the gc request).

[ekexium]

I noticed that the gc function does not use the gc request, which is a bit confusing. AIUI, we currently gc locks but not deleted data (the delete ranges step) or old data (which uses the gc request).

The new GC mechanism(https://docs.pingcap.com/tidb/stable/garbage-collection-overview#do-gc) only requires updating safepoint on PD. "TiKV automatically detects the change of safe point and performs GC for all Region leaders on the current node."

[nrc]

The link is broken for me. Does that mean we don't need to support the gc message at all?

[ekexium]

Yes, I think. The link is updated.

[nrc]

@ekexium is it ok to close this issue now? We have a gc function, which I think does what it should.

[ekexium]

GC support is not in perfect state, so I prefer to keep it open.

The gc function is not well tested yet. And I think there are open questions. For example, should we provide automatic GC?

[andylokandy]

I've written up an RFC for future work on GC refractory. Once this is implemented, the client may need to support editing GC barrier via PD.

[frostyplanet]

What's the status of the GC feature ?

[andylokandy]

It's still the same.

[frostyplanet]

May I ask the difference of current implementation from the one in tikv/client-go code ?