forked from cockroachdb/cockroach
/
session.go
613 lines (554 loc) · 22.4 KB
/
session.go
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// Copyright 2015 The Cockroach Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License.
//
// Author: Vivek Menezes (vivek@cockroachlabs.com)
// Author: Andrei Matei (andreimatei1@gmail.com)
package sql
import (
"fmt"
"net"
"time"
opentracing "github.com/opentracing/opentracing-go"
"github.com/pkg/errors"
"golang.org/x/net/context"
"github.com/cockroachdb/cockroach/pkg/base"
"github.com/cockroachdb/cockroach/pkg/config"
"github.com/cockroachdb/cockroach/pkg/internal/client"
"github.com/cockroachdb/cockroach/pkg/roachpb"
"github.com/cockroachdb/cockroach/pkg/sql/mon"
"github.com/cockroachdb/cockroach/pkg/sql/parser"
"github.com/cockroachdb/cockroach/pkg/sql/sqlbase"
"github.com/cockroachdb/cockroach/pkg/storage/engine/enginepb"
"github.com/cockroachdb/cockroach/pkg/util"
"github.com/cockroachdb/cockroach/pkg/util/envutil"
"github.com/cockroachdb/cockroach/pkg/util/log"
"github.com/cockroachdb/cockroach/pkg/util/retry"
"github.com/cockroachdb/cockroach/pkg/util/timeutil"
"github.com/cockroachdb/cockroach/pkg/util/tracing"
)
// COCKROACH_TRACE_SQL=duration can be used to log SQL transactions that take
// longer than duration to complete. For example, COCKROACH_TRACE_SQL=1s will
// log the trace for any transaction that takes 1s or longer. To log traces for
// all transactions use COCKROACH_TRACE_SQL=1ns. Note that any positive
// duration will enable tracing and will slow down all execution because traces
// are gathered for all transactions even if they are not output.
var traceSQLDuration = envutil.EnvOrDefaultDuration("COCKROACH_TRACE_SQL", 0)
var traceSQL = traceSQLDuration > 0
// COCKROACH_DISABLE_SQL_EVENT_LOG can be used to disable the event log that is
// normally kept for every SQL connection. The event log has a non-trivial
// performance impact.
var disableSQLEventLog = envutil.EnvOrDefaultBool("COCKROACH_DISABLE_SQL_EVENT_LOG", false)
// COCKROACH_TRACE_7881 can be used to trace all SQL transactions, in the hope
// that we'll catch #7881 and dump the current trace for debugging.
var traceSQLFor7881 = envutil.EnvOrDefaultBool("COCKROACH_TRACE_7881", false)
// span baggage key used for marking a span
const keyFor7881Sample = "found#7881"
// Session contains the state of a SQL client connection.
// Create instances using NewSession().
type Session struct {
//
// Session parameters, user-configurable.
//
// ApplicationName is the name of the application running the
// current session. This can be used for logging and per-application
// statistics. Change via resetApplicationName().
ApplicationName string
// Database indicates the "current" database for the purpose of
// resolving names. See searchAndQualifyDatabase() for details.
Database string
// DefaultIsolationLevel indicates the default isolation level of
// newly created transactions.
DefaultIsolationLevel enginepb.IsolationType
// DistSQLMode indicates whether to run queries using the distributed
// execution engine.
DistSQLMode distSQLExecMode
// Location indicates the current time zone.
Location *time.Location
// SearchPath is a list of databases that will be searched for a table name
// before the database. Currently, this is used only for SELECTs.
// Names in the search path must have been normalized already.
SearchPath parser.SearchPath
// Syntax determine which lexical structure to use for parsing.
Syntax parser.Syntax
// User is the name of the user logged into the session.
User string
//
// State structures for the logical SQL session.
//
// TxnState carries information about the open transaction (if any),
// including the retry status and the KV client Txn object.
TxnState txnState
// PreparedStatements and PreparedPortals store the statements/portals
// that have been prepared via pgwire.
PreparedStatements PreparedStatements
PreparedPortals PreparedPortals
// virtualSchemas aliases Executor.virtualSchemas.
// It is duplicated in Session to provide easier access to
// the various methods that need this reference.
// TODO(knz): place this in an executionContext parameter-passing
// structure.
virtualSchemas virtualSchemaHolder
//
// Run-time state.
//
// execCfg is the configuration of the Executor that is executing this
// session.
execCfg *ExecutorConfig
// planner is the planner in charge of executing statements within this
// session. While the planner type is logically scoped to the execution
// of a single statement, this field will be reset and reused between
// statements. When necessary, it can be cloned so that future modifications
// to the field do not affect a separate stream of statement execution.
planner planner
// distSQLPlanner is in charge of distSQL physical planning and running
// logic.
distSQLPlanner *distSQLPlanner
// context is the Session's base context, to be used for all
// SQL-related logging. See Ctx().
context context.Context
// finishEventLog indicates whether an event log was started for
// this session.
finishEventLog bool
// cancel is a method to call when the session terminates, to
// release resources associated with the context above.
// TODO(andrei): We need to either get rid of this cancel field, or
// it needs to move to the TxnState and become a per-txn
// cancel. Right now, we're cancelling all the txns that have ever
// run on this session when the session is closed, as opposed to
// cancelling the individual transactions as soon as they
// COMMIT/ROLLBACK.
cancel context.CancelFunc
// mon tracks memory usage for SQL activity within this session. It
// is not directly used, but rather indirectly used via sessionMon
// and TxnState.mon. sessionMon tracks session-bound objects like prepared
// statements and result sets.
//
// The reason why TxnState.mon and mon are split is to enable
// separate reporting of statistics per transaction and per
// session. This is because the "interesting" behavior w.r.t memory
// is typically caused by transactions, not sessions. The reason why
// sessionMon and mon are split is to enable separate reporting of
// statistics for result sets (which escape transactions).
mon mon.MemoryMonitor
sessionMon mon.MemoryMonitor
// leases holds the state of per-table leases acquired by the leaseMgr.
leases []*LeaseState
// leaseMgr manages acquiring and releasing per-table leases.
leaseMgr *LeaseManager
// systemConfig holds a copy of the latest system config since the last
// call to resetForBatch.
systemConfig config.SystemConfig
// databaseCache is used as a cache for database names.
// TODO(andrei): get rid of it and replace it with a leasing system for
// database descriptors.
databaseCache *databaseCache
// If set, contains the in progress COPY FROM columns.
copyFrom *copyNode
//
// Per-session statistics.
//
// memMetrics track memory usage by SQL execution.
memMetrics *MemoryMetrics
// sqlStats tracks per-application statistics for all
// applications on each node.
sqlStats *sqlStats
// appStats track per-application SQL usage statistics.
appStats *appStats
// noCopy is placed here to guarantee that Session objects are not
// copied.
noCopy util.NoCopy
}
// SessionArgs contains arguments for creating a new Session with NewSession().
type SessionArgs struct {
Database string
User string
ApplicationName string
}
// NewSession creates and initializes a new Session object.
// remote can be nil.
func NewSession(
ctx context.Context, args SessionArgs, e *Executor, remote net.Addr, memMetrics *MemoryMetrics,
) *Session {
ctx = e.AnnotateCtx(ctx)
cfg, cache := e.getSystemConfig()
s := &Session{
Database: args.Database,
SearchPath: parser.SearchPath{"pg_catalog"},
Location: time.UTC,
User: args.User,
virtualSchemas: e.virtualSchemas,
execCfg: &e.cfg,
distSQLPlanner: e.distSQLPlanner,
leaseMgr: e.cfg.LeaseManager,
systemConfig: cfg,
databaseCache: cache,
memMetrics: memMetrics,
sqlStats: &e.sqlStats,
}
s.planner = planner{
session: s,
}
s.planner.phaseTimes[sessionInit] = timeutil.Now()
s.resetApplicationName(args.ApplicationName)
s.PreparedStatements = makePreparedStatements(s)
s.PreparedPortals = makePreparedPortals(s)
if !disableSQLEventLog && opentracing.SpanFromContext(ctx) == nil {
remoteStr := "<admin>"
if remote != nil {
remoteStr = remote.String()
}
// Set up an EventLog for session events.
ctx = log.WithEventLog(ctx, fmt.Sprintf("sql [%s]", args.User), remoteStr)
s.finishEventLog = true
}
s.context, s.cancel = context.WithCancel(ctx)
return s
}
// Finish releases resources held by the Session.
func (s *Session) Finish(e *Executor) {
if s.mon == (mon.MemoryMonitor{}) {
// This check won't catch the cases where Finish is never called, but it's
// proven to be easier to remember to call Finish than it is to call
// StartMonitor.
panic("session.Finish: session monitors were never initialized. Missing call " +
"to session.StartMonitor?")
}
// If we're inside a txn, roll it back.
if s.TxnState.State.kvTxnIsOpen() {
s.TxnState.updateStateAndCleanupOnErr(
errors.Errorf("session closing"), e)
}
if s.TxnState.State != NoTxn {
s.TxnState.finishSQLTxn(s.context)
}
// Cleanup leases. We might have unreleased leases if we're finishing the
// session abruptly in the middle of a transaction, or, until #7648 is
// addressed, there might be leases accumulated by preparing statements.
s.planner.releaseLeases(s.context)
s.ClearStatementsAndPortals(s.context)
s.sessionMon.Stop(s.context)
s.mon.Stop(s.context)
if s.finishEventLog {
log.FinishEventLog(s.context)
}
// This will stop the heartbeating of the of the txn record.
// TODO(andrei): This shouldn't have any effect, since, if there was a
// transaction, we just explicitly rolled it back above, so the heartbeat loop
// in the TxnCoordSender should not be waiting on this channel any more.
// Consider getting rid of this cancel field all-together.
s.cancel()
}
// Ctx returns the current context for the session: if there is an active SQL
// transaction it returns the transaction context, otherwise it returns the
// session context.
// Note that in some cases we may want the session context even if there is an
// active transaction (an example is when we want to log an event to the session
// event log); in that case s.context should be used directly.
func (s *Session) Ctx() context.Context {
if s.TxnState.State != NoTxn {
return s.TxnState.Ctx
}
return s.context
}
// hijackCtx changes the current transaction's context to the provided one and
// returns a cleanup function to be used to restore the original context when
// the hijack is no longer needed.
// TODO(andrei): delete this when EXPLAIN(TRACE) goes away
func (s *Session) hijackCtx(ctx context.Context) func() {
if s.TxnState.State != Open {
// This hijacking is dubious to begin with. Let's at least assert it's being
// done when the TxnState is in an expected state. In particular, if the
// state would be NoTxn, then we'd need to hijack session.Ctx instead of the
// txnState's context.
log.Fatalf(ctx, "can only hijack while a SQL txn is Open. txnState: %+v",
&s.TxnState)
}
return s.TxnState.hijackCtx(ctx)
}
// TxnStateEnum represents the state of a SQL txn.
type TxnStateEnum int
//go:generate stringer -type=TxnStateEnum
const (
// No txn is in scope. Either there never was one, or it got committed/rolled back.
NoTxn TxnStateEnum = iota
// A txn is in scope.
Open
// The txn has encountered a (non-retriable) error.
// Statements will be rejected until a COMMIT/ROLLBACK is seen.
Aborted
// The txn has encountered a retriable error.
// Statements will be rejected until a RESTART_TRANSACTION is seen.
RestartWait
// The KV txn has been committed successfully through a RELEASE.
// Statements are rejected until a COMMIT is seen.
CommitWait
)
// Some states mean that a client.Txn is open, others don't.
func (s TxnStateEnum) kvTxnIsOpen() bool {
return s == Open || s == RestartWait
}
// txnState contains state associated with an ongoing SQL txn.
// There may or may not be an open KV txn associated with the SQL txn.
// For interactive transactions (open across batches of SQL commands sent by a
// user), txnState is intended to be stored as part of a user Session.
type txnState struct {
txn *client.Txn
State TxnStateEnum
// Ctx is the context for everything running in this SQL txn.
Ctx context.Context
// retrying is used to work around the non-idempotence of SAVEPOINT
// queries.
//
// See the comment at the site of its use for more detail.
retrying bool
// If set, the user declared the intention to retry the txn in case of retriable
// errors. The txn will enter a RestartWait state in case of such errors.
retryIntent bool
// The transaction will be retried in case of retriable error. The retry will be
// automatic (done by Txn.Exec()). This field behaves the same as retryIntent,
// except it's reset in between client round trips.
autoRetry bool
// A COMMIT statement has been processed. Useful for allowing the txn to
// survive retriable errors if it will be auto-retried (BEGIN; ... COMMIT; in
// the same batch), but not if the error needs to be reported to the user.
commitSeen bool
// The schema change closures to run when this txn is done.
schemaChangers schemaChangerCollection
sp opentracing.Span
// When COCKROACH_TRACE_SQL is enabled, trace accumulates spans as
// they're closed. All the spans pertain to the current txn.
trace *tracing.RecordedTrace
// The timestamp to report for current_timestamp(), now() etc.
// This must be constant for the lifetime of a SQL transaction.
sqlTimestamp time.Time
// mon tracks txn-bound objects like the running state of
// planNode in the midst of performing a computation. We
// host this here instead of TxnState because TxnState is
// fully reset upon each call to resetForNewSQLTxn().
mon mon.MemoryMonitor
}
// resetForNewSQLTxn (re)initializes the txnState for a new transaction.
// It creates a new client.Txn and initializes it using the session defaults.
// txnState.State will be set to Open.
func (ts *txnState) resetForNewSQLTxn(e *Executor, s *Session) {
if ts.sp != nil {
panic(fmt.Sprintf("txnState.reset() called on ts with active span. How come "+
"finishSQLTxn() wasn't called previously? ts: %+v", ts))
}
// Reset state vars to defaults.
ts.retrying = false
ts.retryIntent = false
ts.autoRetry = false
ts.commitSeen = false
// Create a context for this transaction. It will include a
// root span that will contain everything executed as part of the
// upcoming SQL txn, including (automatic or user-directed) retries.
// The span is closed by finishSQLTxn().
// TODO(andrei): figure out how to close these spans on server shutdown? Ties
// into a larger discussion about how to drain SQL and rollback open txns.
ctx := s.context
if traceSQL {
var err error
ctx, ts.trace, err = tracing.StartSnowballTrace(ctx, "traceSQL")
if err != nil {
log.Fatalf(ctx, "unable to create snowball tracer: %s", err)
}
} else if traceSQLFor7881 {
var err error
ctx, ts.trace, err = tracing.NewTracerAndSpanFor7881(ctx)
if err != nil {
log.Fatalf(ctx, "couldn't create a tracer for debugging #7881: %s", err)
}
} else {
var sp opentracing.Span
if parentSp := opentracing.SpanFromContext(ctx); parentSp != nil {
// Create a child span for this SQL txn.
tracer := parentSp.Tracer()
sp = tracer.StartSpan("sql txn", opentracing.ChildOf(parentSp.Context()))
} else {
// Create a root span for this SQL txn.
tracer := e.cfg.AmbientCtx.Tracer
sp = tracer.StartSpan("sql txn")
}
// Put the new span in the context.
ctx = opentracing.ContextWithSpan(ctx, sp)
}
ts.sp = opentracing.SpanFromContext(ctx)
ts.Ctx = ctx
ts.mon.Start(ctx, &s.mon, mon.BoundAccount{})
ts.txn = client.NewTxn(e.cfg.DB)
if err := ts.txn.SetIsolation(s.DefaultIsolationLevel); err != nil {
panic(err)
}
ts.State = Open
// Discard the old schemaChangers, if any.
ts.schemaChangers = schemaChangerCollection{}
}
// willBeRetried returns true if the SQL transaction is going to be retried
// because of err.
func (ts *txnState) willBeRetried() bool {
return ts.autoRetry || ts.retryIntent
}
// resetStateAndTxn moves the txnState into a specified state, as a result of
// the client.Txn being done.
func (ts *txnState) resetStateAndTxn(state TxnStateEnum) {
if state != NoTxn && state != Aborted && state != CommitWait {
panic(fmt.Sprintf("resetStateAndTxn called with unsupported state: %s", state))
}
if ts.txn != nil && !ts.txn.IsFinalized() {
panic(fmt.Sprintf(
"attempting to move SQL txn to state %s inconsistent with KV txn state: %s "+
"(finalized: false)", state, ts.txn.Proto().Status))
}
ts.State = state
ts.txn = nil
}
// finishSQLTxn closes the root span for the current SQL txn.
// This needs to be called before resetForNewSQLTransaction() is called for
// starting another SQL txn.
// The session context is just used for logging the SQL trace.
func (ts *txnState) finishSQLTxn(sessionCtx context.Context) {
ts.mon.Stop(ts.Ctx)
if ts.sp == nil {
panic("No span in context? Was resetForNewSQLTxn() called previously?")
}
sampledFor7881 := (ts.sp.BaggageItem(keyFor7881Sample) != "")
ts.sp.Finish()
ts.sp = nil
if (traceSQL && timeutil.Since(ts.sqlTimestamp) >= traceSQLDuration) ||
(traceSQLFor7881 && sampledFor7881) {
dump := tracing.FormatRawSpans(ts.trace.GetSpans())
if len(dump) > 0 {
log.Infof(sessionCtx, "SQL trace:\n%s", dump)
}
}
}
// updateStateAndCleanupOnErr updates txnState based on the type of error that we
// received. If it's a retriable error and we're going to retry the txn,
// then the state moves to RestartWait. Otherwise, the state moves to Aborted
// and the KV txn is cleaned up.
func (ts *txnState) updateStateAndCleanupOnErr(err error, e *Executor) {
if err == nil {
panic("updateStateAndCleanupOnErr called with no error")
}
if retErr, ok := err.(*roachpb.RetryableTxnError); !ok ||
!ts.willBeRetried() ||
!ts.txn.IsRetryableErrMeantForTxn(retErr) {
// We can't or don't want to retry this txn, so the txn is over.
e.TxnAbortCount.Inc(1)
// This call rolls back a PENDING transaction and cleans up all its
// intents.
ts.txn.CleanupOnError(ts.Ctx, err)
ts.resetStateAndTxn(Aborted)
} else {
// If we got a retriable error, move the SQL txn to the RestartWait state.
// Note that TransactionAborted is also a retriable error, handled here;
// in this case cleanup for the txn has been done for us under the hood.
ts.State = RestartWait
}
}
// hijackCtx changes the transaction's context to the provided one and returns a
// cleanup function to be used to restore the original context when the hijack
// is no longer needed.
// TODO(andrei): delete this when EXPLAIN(TRACE) goes away.
func (ts *txnState) hijackCtx(ctx context.Context) func() {
origCtx := ts.Ctx
ts.Ctx = ctx
return func() {
ts.Ctx = origCtx
}
}
type schemaChangerCollection struct {
// A schemaChangerCollection accumulates schemaChangers from potentially
// multiple user requests, part of the same SQL transaction. We need to
// remember what group and index within the group each schemaChanger came
// from, so we can map failures back to the statement that produced them.
curGroupNum int
// The index of the current statement, relative to its group. For statements
// that have been received from the client in the same batch, the
// group consists of all statements in the same transaction.
curStatementIdx int
// schema change callbacks together with the index of the statement
// that enqueued it (within its group of statements).
schemaChangers []struct {
epoch int
idx int
sc SchemaChanger
}
}
func (scc *schemaChangerCollection) queueSchemaChanger(schemaChanger SchemaChanger) {
scc.schemaChangers = append(
scc.schemaChangers,
struct {
epoch int
idx int
sc SchemaChanger
}{scc.curGroupNum, scc.curStatementIdx, schemaChanger})
}
// execSchemaChanges releases schema leases and runs the queued
// schema changers. This needs to be run after the transaction
// scheduling the schema change has finished.
//
// The list of closures is cleared after (attempting) execution.
//
// Args:
// results: The results from all statements in the group that scheduled the
// schema changes we're about to execute. Results corresponding to the
// schema change statements will be changed in case an error occurs.
func (scc *schemaChangerCollection) execSchemaChanges(
ctx context.Context, e *Executor, planMaker *planner, results ResultList,
) {
if planMaker.txn != nil {
panic("trying to execute schema changes while still in a transaction")
}
// Release the leases once a transaction is complete.
planMaker.releaseLeases(ctx)
if e.cfg.SchemaChangerTestingKnobs.SyncFilter != nil {
e.cfg.SchemaChangerTestingKnobs.SyncFilter(TestingSchemaChangerCollection{scc})
}
// Execute any schema changes that were scheduled, in the order of the
// statements that scheduled them.
for _, scEntry := range scc.schemaChangers {
sc := &scEntry.sc
sc.db = *e.cfg.DB
sc.testingKnobs = e.cfg.SchemaChangerTestingKnobs
sc.distSQLPlanner = e.distSQLPlanner
for r := retry.Start(base.DefaultRetryOptions()); r.Next(); {
if err := sc.exec(ctx); err != nil {
if err != errExistingSchemaChangeLease {
log.Warningf(ctx, "Error executing schema change: %s", err)
}
if err == sqlbase.ErrDescriptorNotFound {
} else if sqlbase.IsIntegrityConstraintError(err) {
// All constraint violations can be reported; we report it as the result
// corresponding to the statement that enqueued this changer.
// There's some sketchiness here: we assume there's a single result
// per statement and we clobber the result/error of the corresponding
// statement.
// There's also another subtlety: we can only report results for
// statements in the current batch; we can't modify the results of older
// statements.
if scEntry.epoch == scc.curGroupNum {
results[scEntry.idx] = Result{Err: err}
}
} else {
// retryable error.
continue
}
}
break
}
}
scc.schemaChangers = scc.schemaChangers[:0]
}