Coprocessor will get invalid collation ID from TiDB

[Defined2014]

When add a warning log at GetCharsetInfoByID(link), it will be flooded by logs. From the log, we could get the collation ID is 0, seems it not be set in TiDB (not sure about it, just guess).

The error log is below,
[2021/11/11 16:19:47.624 +08:00] [ERROR] [cop_handler.go:453] ["Unable to get collation name from ID, use default collation instead."] [ID=0] [stack="github.com/pingcap/tidb/store/mockstore/unistore/cophandler.fieldTypeFromPBColumn\n\t/Users/jasonmo/tidb/store/mockstore/unistore/cophandler/cop_handler.go:456\ngithub.com/pingcap/tidb/store/mockstore/unistore/cophandler.(*evalContext).setColumnInfo\n\t/Users/jasonmo/tidb/store/mockstore/unistore/cophandler/cop_handler.go:205\ngithub.com/pingcap/tidb/store/mockstore/unistore/cophandler.newClosureExecutor\n\t/Users/jasonmo/tidb/store/mockstore/unistore/cophandler/closure_exec.go:248\ngithub.com/pingcap/tidb/store/mockstore/unistore/cophandler.buildClosureExecutor\n\t/Users/jasonmo/tidb/store/mockstore/unistore/cophandler/closure_exec.go:170\ngithub.com/pingcap/tidb/store/mockstore/unistore/cophandler.handleCopDAGRequest\n\t/Users/jasonmo/tidb/store/mockstore/unistore/cophandler/cop_handler.go:118\ngithub.com/pingcap/tidb/store/mockstore/unistore/cophandler.HandleCopRequestWithMPPCtx\n\t/Users/jasonmo/tidb/store/mockstore/unistore/cophandler/cop_handler.go:71\ngithub.com/pingcap/tidb/store/mockstore/unistore/cophandler.HandleCopRequest\n\t/Users/jasonmo/tidb/store/mockstore/unistore/cophandler/cop_handler.go:59\ngithub.com/pingcap/tidb/store/mockstore/unistore/tikv.(*Server).Coprocessor\n\t/Users/jasonmo/tidb/store/mockstore/unistore/tikv/server.go:565\ngithub.com/pingcap/tidb/store/mockstore/unistore.(*RPCClient).SendRequest\n\t/Users/jasonmo/tidb/store/mockstore/unistore/rpc.go:236\ngithub.com/pingcap/tidb/store/mockstore.(*clientRedirector).SendRequest\n\t/Users/jasonmo/tidb/store/mockstore/redirector.go:61\ngithub.com/tikv/client-go/v2/internal/client.reqCollapse.SendRequest\n\t/Users/jasonmo/go/pkg/mod/github.com/tikv/client-go/[email protected]/internal/client/client_collapse.go:74\ngithub.com/tikv/client-go/v2/internal/locate.(*RegionRequestSender).sendReqToRegion\n\t/Users/jasonmo/go/pkg/mod/github.com/tikv/client-go/[email protected]/internal/locate/region_request.go:1128\ngithub.com/tikv/client-go/v2/internal/locate.(*RegionRequestSender).SendReqCtx\n\t/Users/jasonmo/go/pkg/mod/github.com/tikv/client-go/[email protected]/internal/locate/region_request.go:980\ngithub.com/tikv/client-go/v2/txnkv/txnsnapshot.(*ClientHelper).SendReqCtx\n\t/Users/jasonmo/go/pkg/mod/github.com/tikv/client-go/[email protected]/txnkv/txnsnapshot/client_helper.go:108\ngithub.com/pingcap/tidb/store/copr.(*copIteratorWorker).handleTaskOnce\n\t/Users/jasonmo/tidb/store/copr/coprocessor.go:731\ngithub.com/pingcap/tidb/store/copr.(*copIteratorWorker).handleTask\n\t/Users/jasonmo/tidb/store/copr/coprocessor.go:645\ngithub.com/pingcap/tidb/store/copr.(*copIteratorWorker).run\n\t/Users/jasonmo/tidb/store/copr/coprocessor.go:382"]

[bb7133]

This is kind of expected: before introducing the new collation framework, collation id is meaningless for TiDB(there is only 1 collation for each charset). So for a lot of codes, the collation ID may be missing.

We probably need to fix it eventually with the code refactoring/testing enhancements.

[bb7133]

/cc @wjhuang2016

[wjhuang2016]

// NewExtraHandleColInfo mocks a column info for extra handle column.
func NewExtraHandleColInfo() *ColumnInfo {
	colInfo := &ColumnInfo{
		ID:   ExtraHandleID,
		Name: ExtraHandleName,
	}
	colInfo.Flag = mysql.PriKeyFlag | mysql.NotNullFlag
	colInfo.Tp = mysql.TypeLonglong
	colInfo.Flen, colInfo.Decimal = mysql.GetDefaultFieldLengthAndDecimal(mysql.TypeLonglong)
	return colInfo
}

We doesn't set charset and collation for _tidb_rowid.