See https://github.com/tikv/client-go/blob/5945fe392067dab939cd642e4d3ccd3bd9f8e5e2/internal/locate/region_cache.go#L154.

If we want to support TiDB SQL in other languages, we must need a coprocessor support.

Compile error in google test when using -DENABLE_TESTS=on.

 error: definition of implicit copy constructor for 'StartsWithMatcher<std::wstring>' is deprecated because it has a user-declared copy assignment operator

./pd-server --version
Release Version: v4.0.0-rc.2-563-gaa22efb5-dirty
Edition: Community
Git Commit Hash: aa22efb50906e2d0fb1306bd2af6813969e46d73
Git Branch: master
UTC Build Time: 2021-05-27 04:38:59

Release Version: 5.1.0-alpha
Edition: Community
Git Commit Hash: cd905a208293c2b0c1fca9aa2756d5c26392b38c
Git Commit Branch: master
UTC Build Time: 2021-05-28 09:25:25
Rust Version: rustc 1.53.0-nightly (16bf626a3 2021-04-14)
Enable Features: jemalloc mem-profiling portable sse protobuf-codec test-engines-rocksdb cloud-aws cloud-gcp
Profile: release

src:
count=1000000
Txn txn(test_cluster.get());

try{
    char keyName[32];
    std::string keyValue( 512, 'x');

    auto begin_tm = timeSinceEpochMillisec();
    for( int i = 1;i<=count;i++){
        sprintf(keyName, "c%d", i);
        txn.set(keyName, keyValue);
    }
    txn.commit();
    auto end_tm = timeSinceEpochMillisec();
    printf("time:%ld\n", end_tm- begin_tm);
}
catch ( Exception & e) {
    std::cerr << "exception caught: " << e.displayText() << '\n';
}

[19:42:06] [(0)] Information: load store id 2001 address 172.16.16.21:20160
[19:43:33] [(0)] Warning: region {44103,3,29} find error: EpochNotMatch current epoch of region 44103 is conf_ver: 3 version: 30
[19:43:33] [(0)] Information: region stale for region {44103,3,29}.
[19:43:33] [(0)] Information: try drop region {44103,3,29}
[19:43:33] [(0)] Information: drop region 44103 because of send failure
[19:43:33] [(0)] Warning: region {44127,3,30} find error: peer is not leader for region 44127, leader may None
[19:43:33] [(0)] Information: report not leader but doesn't have new leader
[19:43:33] [(0)] Information: try drop region {44127,3,30}
[19:43:33] [(0)] Information: drop region 44127 because of send failure
[19:43:53] [(0)] Warning: write commit exception: Exception: Region epoch not match after retries: Region {44103,3,29} not in region cache.
exception caught: Exception: Region epoch not match after retries: Region {44103,3,29} not in region cache.

TiDB has a background goroutine to check validation of stores periodicly, while client-c will check it as soon as receiving an error.

I think it's better to implement such a eager way to update region cache.

@hanfei1991
Would it be possible to create the "c-client" only with a dependency to "grpc" (e.g. to void "Poco")?

does client-c support deleting at present?

Currently, the MVCC Write is only used by test, some features is yet to add, like rollback asyncly after write fails. Maybe we'd better maintain serveral rollback queues rather than per rollback per thread.

Currently, the keepalive configuration is not set for client.
So if a server is shut down abnormally, the client can not detect the failure of the server side thus it may hang forever.

Currently we only support get gc safe point from grpc api, but indeed, we should get safe point from etcd kv, and check if the safe point is out-date during mvcc scan.

Add compilation options such as：cmake -DENABLE_TESTS=ON ..
This command causes compilation to fail，As mentioned in the pingcap Developer Forum, grpc is compiled with dynamic libraries. The old version of clien-c can be compiled and used temporarily, but the latest version cannot. Moreover, we recommend using static libraries.Please fix it as soon as possible. Thank you

I would recommend creating a separate protocol/processing layer from network layer which will allow for use in different languages and application stacks.
e.g. I would like to use TiKV in OpenResty (Nginx + Lua) stack where Nginx async socket needs to be used for network communication.

Great news!
Once ready, I will add SWIG configuration (https://github.com/swig/swig) to bind this driver to many languages.

add raw kv api for client-c

The git clone protocol of some submodule is ssh, unify the url of submodule to https url.

[submodule "third_party/kvproto"]
	path = third_party/kvproto
	url = [email protected]:pingcap/kvproto.git
[submodule "third_party/googletest"]
	path = third_party/googletest
	url = [email protected]:google/googletest.git
[submodule "third_party/libfiu"]
	path = third_party/libfiu
	url = https://github.com/albertito/libfiu.git

This project should be packed as a shared lib with ffi interface so as to support other languages.

To reduce the overhead of transferring data between the read nodes and the write nodes, we need to make client-c support sending super batch coprocessor requests.
Super batch coprocessor requests help us reduce the network overhead and the read amplification of delta data in the storage layer level.

Reference: https://github.com/pingcap/tidb/blob/v6.1.0/store/copr/batch_coprocessor.go#L675

When init cluster id, should also check error in rpc response, otherwise cluster id maybe zero mistakely. Because PD will not set cluster id if go error, instead it put err msg in rpc response.Error. check here and here