crdb session变量维护堆栈

session默认事务隔离级别

pkg/storage/engine/enginepb/mvcc3.pb.go

type IsolationType int32

const (
	SERIALIZABLE IsolationType = 0
	SNAPSHOT     IsolationType = 1
)

var IsolationType_name = map[int32]string{
	0: "SERIALIZABLE",
	1: "SNAPSHOT",
}

pkg/sql/pgwire/v3.go
pkg/sql/session.go

func NewSession(
	ctx context.Context, args SessionArgs, e *Executor, remote net.Addr, memMetrics *MemoryMetrics,
) *Session {
	ctx = e.AnnotateCtx(ctx)
	distSQLMode := DistSQLExecMode(DistSQLClusterExecMode.Get(&e.cfg.Settings.SV))

	s := &Session{
		Database:              args.Database,
		DefaultIsolationLevel: enginepb.SNAPSHOT,
		DistSQLMode:           distSQLMode,
		SearchPath:            sqlbase.DefaultSearchPath,
		Location:              time.UTC,
		User:                  args.User,
		virtualSchemas:        e.virtualSchemas,
		execCfg:               &e.cfg,

初始化session时，不指定DefaultIsolationLevel，即DefaultIsolationLevel=0.

pkg/sql/executor.go

txnState.resetForNewSQLTxn(
	e, session,
	autoCommit, /* implicitTxn */
	false,      /* retryIntent */
	e.cfg.Clock.PhysicalTime(), /* sqlTimestamp */
	session.DefaultIsolationLevel,
	roachpb.NormalUserPriority,
)

执行语句之前，如果语句不在trx中，则reset其隔离级别为session.DefaultIsolationLevel

set default_transaction_isolation=‘SERIALIZABLE’

0  0x00000000056e1bb7 in github.com/cockroachdb/cockroach/pkg/sql.glob..func82
    at ./pkg/sql/vars.go:169
 1  0x00000000056918ef in github.com/cockroachdb/cockroach/pkg/sql.(*setNode).Start
    at ./pkg/sql/set.go:106
 2  0x000000000566863c in github.com/cockroachdb/cockroach/pkg/sql.(*planner).startPlan
    at ./pkg/sql/plan.go:225
 3  0x000000000561e361 in github.com/cockroachdb/cockroach/pkg/sql.(*Executor).execClassic
    at ./pkg/sql/executor.go:1984
 4  0x000000000561f529 in github.com/cockroachdb/cockroach/pkg/sql.(*Executor).execStmt
    at ./pkg/sql/executor.go:2156
 5  0x000000000561c7ba in github.com/cockroachdb/cockroach/pkg/sql.(*Executor).execStmtInOpenTxn
    at ./pkg/sql/executor.go:1795
 6  0x000000000561af78 in github.com/cockroachdb/cockroach/pkg/sql.(*Executor).execSingleStatement
    at ./pkg/sql/executor.go:1315
 7  0x000000000561a45c in github.com/cockroachdb/cockroach/pkg/sql.runTxnAttempt
    at ./pkg/sql/executor.go:1190
 8  0x00000000056191bc in github.com/cockroachdb/cockroach/pkg/sql.runWithAutoRetry
    at ./pkg/sql/executor.go:1016
 9  0x0000000005617f3e in github.com/cockroachdb/cockroach/pkg/sql.(*Executor).execParsed
    at ./pkg/sql/executor.go:833
10  0x0000000005617aa1 in github.com/cockroachdb/cockroach/pkg/sql.(*Executor).execRequest

show all

 0  0x00000000056e1edf in github.com/cockroachdb/cockroach/pkg/sql.glob..func83
    at ./pkg/sql/vars.go:184
 1  0x00000000056d960a in github.com/cockroachdb/cockroach/pkg/sql.glob..func18
    at ./pkg/sql/crdb_internal.go:626
 2  0x00000000056f73c0 in github.com/cockroachdb/cockroach/pkg/sql.virtualTableEntry.getPlanInfo.func1
    at ./pkg/sql/virtual_schema.go:121
 3  0x00000000056e5bd5 in github.com/cockroachdb/cockroach/pkg/sql.(*planner).getVirtualDataSource.func1
    at ./pkg/sql/data_source.go:321
 4  0x0000000005624744 in github.com/cockroachdb/cockroach/pkg/sql.doExpandPlan
    at ./pkg/sql/expand_plan.go:238
 5  0x000000000562580a in github.com/cockroachdb/cockroach/pkg/sql.expandRenderNode
    at ./pkg/sql/expand_plan.go:330
 6  0x0000000005623a98 in github.com/cockroachdb/cockroach/pkg/sql.doExpandPlan
    at ./pkg/sql/expand_plan.go:234
 7  0x00000000056225e3 in github.com/cockroachdb/cockroach/pkg/sql.(*planner).expandPlan
    at ./pkg/sql/expand_plan.go:33
 8  0x000000000565e9eb in github.com/cockroachdb/cockroach/pkg/sql.(*planner).optimizePlan
    at ./pkg/sql/optimize.go:46
 9  0x00000000056681f9 in github.com/cockroachdb/cockroach/pkg/sql.(*planner).makePlan
    at ./pkg/sql/plan.go:202
10  0x000000000561efea in github.com/cockroachdb/cockroach/pkg/sql.(*Executor).execStmt
    at ./pkg/sql/executor.go:2129
11  0x000000000561c7ba in github.com/cockroachdb/cockroach/pkg/sql.(*Executor).execStmtInOpenTxn
    at ./pkg/sql/executor.go:1795
12  0x000000000561af78 in github.com/cockroachdb/cockroach/pkg/sql.(*Executor).execSingleStatement
    at ./pkg/sql/executor.go:1315
13  0x000000000561a45c in github.com/cockroachdb/cockroach/pkg/sql.runTxnAttempt
    at ./pkg/sql/executor.go:1190
14  0x00000000056191bc in github.com/cockroachdb/cockroach/pkg/sql.runWithAutoRetry
    at ./pkg/sql/executor.go:1016
15  0x0000000005617f3e in github.com/cockroachdb/cockroach/pkg/sql.(*Executor).execParsed
    at ./pkg/sql/executor.go:833
16  0x0000000005617aa1 in github.com/cockroachdb/cockroach/pkg/sql.(*Executor).execRequest
    at ./pkg/sql/executor.go:744
17  0x0000000005616ecb in github.com/cockroachdb/cockroach/pkg/sql.(*Executor).ExecuteStatements
    at ./pkg/sql/executor.go:629
18  0x0000000005777ec7 in github.com/cockroachdb/cockroach/pkg/sql/pgwire.(*v3Conn).handleSimpleQuery