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txn: also update the @@tidb_last_txn_info for readyonly or rollback txns #61057

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Merged
merged 3 commits into from
May 13, 2025
Merged

txn: also update the @@tidb_last_txn_info for readyonly or rollback txns #61057

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dfb71cb
txn: also update the `@@tidb_last_txn_info` for readyonly or rollback…
lcwangchao May 9, 2025
0a408fa
use json to marshal
lcwangchao May 12, 2025
d467fda
Update pkg/session/session.go
lcwangchao May 13, 2025
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5 changes: 5 additions & 0 deletions pkg/executor/adapter.go
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Original file line number Diff line number Diff line change
Expand Up @@ -330,6 +330,11 @@ func (a *ExecStmt) PointGet(ctx context.Context) (*recordSet, error) {
exec.Recreated(pointGetPlan, a.Ctx)
a.PsStmt.PointGet.Executor = exec
executor = exec
// If reuses the executor, the executor build phase is skipped, and the txn will not be activated that
// caused `TxnCtx.StartTS` to be 0.
// So we should set the `TxnCtx.StartTS` manually here to make sure it is not 0
// to provide the right value for `@@tidb_last_txn_info` or other variables.
a.Ctx.GetSessionVars().TxnCtx.StartTS = startTs
}
}

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94 changes: 77 additions & 17 deletions pkg/executor/test/executor/executor_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ import (
"archive/zip"
"context"
"fmt"
"math"
"math/rand"
"os"
"path/filepath"
Expand Down Expand Up @@ -531,51 +532,110 @@ func TestTiDBLastTxnInfo(t *testing.T) {
tk.MustExec("use test")
tk.MustExec("drop table if exists t")
tk.MustExec("create table t (a int primary key)")
tk.MustQuery("select @@tidb_last_txn_info").Check(testkit.Rows(""))
// prepare point get
pointGetStmtID, _, _, err := tk.Session().PrepareStmt("select a from t where a = 1024")
require.NoError(t, err)
// first execute short path point-get
rs, err := tk.Session().ExecutePreparedStmt(context.Background(), pointGetStmtID, nil)
require.NoError(t, err)
tk.ResultSetToResult(rs, fmt.Sprintf("%v", rs)).Check(nil)
tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts')").Check(
testkit.Rows(strconv.FormatUint(math.MaxUint64, 10)),
)

// autocommit txn
tk.MustExec("insert into t values (1)")
rows1 := tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts')").Rows()
require.Greater(t, rows1[0][0].(string), "0")
require.Less(t, rows1[0][0].(string), rows1[0][1].(string))
startTS1, err := strconv.ParseUint(rows1[0][0].(string), 10, 64)
require.NoError(t, err)
commitTS1 := tk.Session().GetSessionVars().LastCommitTS
require.Less(t, startTS1, commitTS1)
require.Equal(t, strconv.FormatUint(commitTS1, 10), rows1[0][1])

// readonly txn should also update @@tidb_last_txn_info
tk.MustExec("begin")
tk.MustQuery("select a from t where a = 1").Check(testkit.Rows("1"))
startTS2 := tk.Session().GetSessionVars().TxnCtx.StartTS
require.Less(t, commitTS1, startTS2)
rows2 := tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts'), @@tidb_current_ts").Rows()
tk.MustExec("commit")
rows3 := tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts')").Rows()
require.Equal(t, rows1[0][0], rows2[0][0])
require.Equal(t, rows1[0][1], rows2[0][1])
require.Equal(t, rows1[0][0], rows3[0][0])
require.Equal(t, rows1[0][1], rows3[0][1])
require.Less(t, rows2[0][1], rows2[0][2])
require.Equal(t, strconv.FormatUint(startTS2, 10), rows2[0][2])
tk.MustExec("commit")
rows3 := tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts')").Rows()
require.Equal(t, strconv.FormatUint(startTS2, 10), rows3[0][0])
require.Equal(t, "0", rows3[0][1])

// txn explicitly started with begin
tk.MustExec("begin")
startTS3 := tk.Session().GetSessionVars().TxnCtx.StartTS
require.Less(t, startTS2, startTS3)
tk.MustExec("update t set a = a + 1 where a = 1")
rows4 := tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts'), @@tidb_current_ts").Rows()
require.Equal(t, rows3[0][0], rows4[0][0])
require.Equal(t, rows3[0][1], rows4[0][1])
require.Equal(t, strconv.FormatUint(startTS3, 10), rows4[0][2])
tk.MustExec("commit")
commitTS3 := tk.Session().GetSessionVars().LastCommitTS
require.Less(t, startTS3, commitTS3)
rows5 := tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts')").Rows()
require.Equal(t, rows1[0][0], rows4[0][0])
require.Equal(t, rows1[0][1], rows4[0][1])
require.Equal(t, rows5[0][0], rows4[0][2])
require.Less(t, rows4[0][1], rows4[0][2])
require.Less(t, rows4[0][2], rows5[0][1])
require.Equal(t, strconv.FormatUint(startTS3, 10), rows5[0][0])
require.Equal(t, strconv.FormatUint(commitTS3, 10), rows5[0][1])

// rollback txn
tk.MustExec("begin")
startTS4 := tk.Session().GetSessionVars().TxnCtx.StartTS
require.Less(t, commitTS3, startTS4)
tk.MustExec("update t set a = a + 1 where a = 2")
tk.MustExec("rollback")
rows6 := tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts')").Rows()
require.Equal(t, rows5[0][0], rows6[0][0])
require.Equal(t, rows5[0][1], rows6[0][1])
require.Equal(t, strconv.FormatUint(startTS4, 10), rows6[0][0])
require.Equal(t, "0", rows6[0][1])

// optimistic txn commit failed
tk.MustExec("begin optimistic")
startTS5 := tk.Session().GetSessionVars().TxnCtx.StartTS
require.Less(t, startTS4, startTS5)
tk.MustExec("insert into t values (2)")
err := tk.ExecToErr("commit")
err = tk.ExecToErr("commit")
require.Error(t, err)
rows7 := tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts'), json_extract(@@tidb_last_txn_info, '$.error')").Rows()
require.Greater(t, rows7[0][0], rows5[0][0])
require.Equal(t, strconv.FormatUint(startTS5, 10), rows7[0][0])
require.Equal(t, "0", rows7[0][1])
require.Contains(t, err.Error(), rows7[0][1])

// autocommit=0
tk.MustExec("set @@autocommit=0")
tk.MustExec("update t set a = a + 1 where a = 1")
startTS6 := tk.Session().GetSessionVars().TxnCtx.StartTS
require.Less(t, startTS5, startTS6)
tk.MustExec("commit")
rows8 := tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts')").Rows()
commitTS6 := tk.Session().GetSessionVars().LastCommitTS
require.Less(t, startTS6, commitTS6)
require.Equal(t, strconv.FormatUint(startTS6, 10), rows8[0][0])
require.Equal(t, strconv.FormatUint(commitTS6, 10), rows8[0][1])
tk.MustExec("set @@autocommit=1")

// not active txn
tk.MustQuery("select 1")
require.Equal(t, rows8, tk.MustQuery(
"select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts')").Rows(),
)

// select @@tidb_last_txn_info should not update @@tidb_last_txn_info
require.Equal(t, rows8, tk.MustQuery(
"select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts')").Rows(),
)

// execute short path point-get again to test the cached case
rs, err = tk.Session().ExecutePreparedStmt(context.Background(), pointGetStmtID, nil)
require.NoError(t, err)
tk.ResultSetToResult(rs, fmt.Sprintf("%v", rs)).Check(nil)
tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts')").Check(
testkit.Rows(strconv.FormatUint(math.MaxUint64, 10)),
)

err = tk.ExecToErr("set @@tidb_last_txn_info = '{}'")
require.True(t, terror.ErrorEqual(err, variable.ErrIncorrectScope), fmt.Sprintf("err: %v", err))
}
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1 change: 1 addition & 0 deletions pkg/session/BUILD.bazel
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Expand Up @@ -130,6 +130,7 @@ go_library(
"@com_github_tikv_client_go_v2//error",
"@com_github_tikv_client_go_v2//oracle",
"@com_github_tikv_client_go_v2//tikv",
"@com_github_tikv_client_go_v2//txnkv/transaction",
"@com_github_tikv_client_go_v2//util",
"@io_etcd_go_etcd_client_v3//:client",
"@io_etcd_go_etcd_client_v3//concurrency",
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24 changes: 24 additions & 0 deletions pkg/session/session.go
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Expand Up @@ -128,6 +128,7 @@ import (
"github.com/pingcap/tidb/pkg/util/tracing"
tikverr "github.com/tikv/client-go/v2/error"
"github.com/tikv/client-go/v2/oracle"
"github.com/tikv/client-go/v2/txnkv/transaction"
tikvutil "github.com/tikv/client-go/v2/util"
"go.uber.org/zap"
"go.uber.org/zap/zapcore"
Expand Down Expand Up @@ -919,6 +920,7 @@ func (s *session) CommitTxn(ctx context.Context) error {
r, ctx := tracing.StartRegionEx(ctx, "session.CommitTxn")
defer r.End()

s.setLastTxnInfoBeforeTxnEnd()
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How about putting it in onTxnEnd?

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Seems onTxnEnd，the txn info has been cleared

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After this line, in doCommitWithRetry -> doCommit, it seems it still have possibility to finally enter a rolled-back state or encounter error. Perhaps it's better to consider put it in a later place where the commit/rollback result is finally determined.

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Seems if a txn comitted or fails to commit, the CommitHook will update it:

tidb/pkg/sessiontxn/isolation/base.go

Line 506 in c71ebaf

txn.SetOption(kv.CommitHook, func(info string, _ error) { sessVars.LastTxnInfo = info })

setLastTxnInfoBeforeTxnEnd in CommitTxn will be overridden at this time. So setLastTxnInfoBeforeTxnEnd is only affects some readonly txns.

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Better to add comments to explain why it is put here.

var commitDetail *tikvutil.CommitDetails
ctx = context.WithValue(ctx, tikvutil.CommitDetailCtxKey, &commitDetail)
err := s.doCommitWithRetry(ctx)
Expand Down Expand Up @@ -957,6 +959,7 @@ func (s *session) RollbackTxn(ctx context.Context) {
r, ctx := tracing.StartRegionEx(ctx, "session.RollbackTxn")
defer r.End()

s.setLastTxnInfoBeforeTxnEnd()
if s.txn.Valid() {
terror.Log(s.txn.Rollback())
}
Expand All @@ -970,6 +973,26 @@ func (s *session) RollbackTxn(ctx context.Context) {
sessiontxn.GetTxnManager(s).OnTxnEnd()
}

// setLastTxnInfoBeforeTxnEnd sets the @@last_txn_info variable before commit/rollback the transaction.
// The `LastTxnInfo` updated with a JSON string that contains start_ts, for_update_ts, etc.
// The `LastTxnInfo` is updated without the `commit_ts` fields because it is unknown
// until the commit is done (or do not need to commit for readonly or a rollback transaction).
// The non-readonly transaction will overwrite the `LastTxnInfo` again after commit to update the `commit_ts` field.
func (s *session) setLastTxnInfoBeforeTxnEnd() {
txnCtx := s.GetSessionVars().TxnCtx
if txnCtx.StartTS == 0 {
// If the txn is not active, for example, executing "SELECT 1", skip setting the last txn info.
return
}

lastTxnInfo, err := json.Marshal(transaction.TxnInfo{
TxnScope: txnCtx.TxnScope,
StartTS: txnCtx.StartTS,
})
terror.Log(err)
s.GetSessionVars().LastTxnInfo = string(lastTxnInfo)
}

func (s *session) GetClient() kv.Client {
return s.client
}
Expand Down Expand Up @@ -2162,6 +2185,7 @@ func (s *session) ExecuteStmt(ctx context.Context, stmtNode ast.StmtNode) (sqlex
var recordSet sqlexec.RecordSet
if stmt.PsStmt != nil { // point plan short path
recordSet, err = stmt.PointGet(ctx)
s.setLastTxnInfoBeforeTxnEnd()
s.txn.changeToInvalid()
} else {
recordSet, err = runStmt(ctx, s, stmt)
Expand Down