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Add a sema to bound the number of inflight vexec queries when getting workflows #8353

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Add a sema to bound the number of inflight vexec queries when getting workflows #8353

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50 changes: 45 additions & 5 deletions go/vt/vtctl/workflow/server.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ package workflow
import (
"context"
"errors"
"flag"
"fmt"
"sort"
"strings"
Expand All @@ -29,6 +30,7 @@ import (
"k8s.io/apimachinery/pkg/util/sets"

"vitess.io/vitess/go/sqltypes"
"vitess.io/vitess/go/sync2"
"vitess.io/vitess/go/trace"
"vitess.io/vitess/go/vt/concurrency"
"vitess.io/vitess/go/vt/key"
Expand All @@ -39,11 +41,17 @@ import (
"vitess.io/vitess/go/vt/vttablet/tmclient"

binlogdatapb "vitess.io/vitess/go/vt/proto/binlogdata"
querypb "vitess.io/vitess/go/vt/proto/query"
topodatapb "vitess.io/vitess/go/vt/proto/topodata"
vtctldatapb "vitess.io/vitess/go/vt/proto/vtctldata"
"vitess.io/vitess/go/vt/proto/vttime"
)

var (
vExecPoolSize = flag.Uint("workflow_server_vexec_pool_size", 1000, "maximum number of concurrent vexec queries to allow")
vExecPoolTimeout = flag.Duration("workflow_server_vexec_pool_default_timeout", time.Millisecond*50, "default timeout to wait acquiring a connection from the vexec pool. zero implies no timeout")
Comment on lines +51 to +52
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@setassociative setassociative Jun 18, 2021

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we should update release notes with this and if we expect to roll out limits per call (imo) we should have a better approach than a flag for concurrency-per-call

)

var (
// ErrInvalidWorkflow is a catchall error type for conditions that should be
// impossible when operating on a workflow.
Expand All @@ -56,6 +64,10 @@ var (
// target keyspaces across different shard primaries. This should be
// impossible.
ErrMultipleTargetKeyspaces = errors.New("multiple target keyspaces for a single workflow")

// ErrVExecConnTimeout is returned if a call to acquire a server's vexecPool
// hits a deadline exceeded
ErrVExecConnTimeout = errors.New("timeout exceeded getting vexec conn")
)

// Server provides an API to work with Vitess workflows, like vreplication
Expand All @@ -66,16 +78,18 @@ var (
// actions on vreplication workflows, and schema migration workflows entirely,
// are not yet supported, but planned.
type Server struct {
ts *topo.Server
tmc tmclient.TabletManagerClient
ts *topo.Server
tmc tmclient.TabletManagerClient
vexecPool *sync2.Semaphore
}

// NewServer returns a new server instance with the given topo.Server and
// TabletManagerClient.
func NewServer(ts *topo.Server, tmc tmclient.TabletManagerClient) *Server {
return &Server{
ts: ts,
tmc: tmc,
ts: ts,
tmc: tmc,
vexecPool: sync2.NewSemaphore(int(*vExecPoolSize), *vExecPoolTimeout),
}
}

Expand All @@ -92,6 +106,8 @@ func (s *Server) CheckReshardingJournalExistsOnTablet(ctx context.Context, table
exists bool
)

// Note we do not use the s.vexecPool semaphore here, to maintain consistent
// behavior with the existing wrangler APIs this function was migrated from.
query := fmt.Sprintf("select val from _vt.resharding_journal where id=%v", migrationID)
p3qr, err := s.tmc.VReplicationExec(ctx, tablet, query)
if err != nil {
Expand Down Expand Up @@ -297,7 +313,13 @@ func (s *Server) GetWorkflows(ctx context.Context, req *vtctldatapb.GetWorkflows
)

vx := vexec.NewVExec(req.Keyspace, "", s.ts, s.tmc)

if !s.vexecPool.AcquireContext(ctx) {
return nil, ErrVExecConnTimeout
}
Comment on lines 315 to +319
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@setassociative setassociative Jun 18, 2021

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tioli:

func NewVExecThrottled(..., pool *sync2.Semaphore) *VExec

and then moving other vexec endpoints over to it is a tiiiiiiny bit less effort; also you don't have to remember to manage locking around each query

results, err := vx.QueryContext(ctx, query)
s.vexecPool.Release()

if err != nil {
return nil, err
}
Expand Down Expand Up @@ -522,7 +544,18 @@ ORDER BY
span.Annotate("keyspace", req.Keyspace)
span.Annotate("workflow", workflow.Name)

results, err := vx.WithWorkflow(workflow.Name).QueryContext(ctx, vrepLogQuery)
var (
results map[*topo.TabletInfo]*querypb.QueryResult
err error
)

if !s.vexecPool.AcquireContext(ctx) {
err = ErrVExecConnTimeout
} else {
results, err = vx.WithWorkflow(workflow.Name).QueryContext(ctx, vrepLogQuery)
s.vexecPool.Release()
}

if err != nil {
// Note that we do not return here. If there are any query results
// in the map (i.e. some tablets returned successfully), we will
Expand Down Expand Up @@ -708,7 +741,14 @@ func (s *Server) getWorkflowCopyStates(ctx context.Context, tablet *topo.TabletI
span.Annotate("vrepl_id", id)

query := fmt.Sprintf("select table_name, lastpk from _vt.copy_state where vrepl_id = %d", id)

if !s.vexecPool.AcquireContext(ctx) {
return nil, ErrVExecConnTimeout
}

qr, err := s.tmc.VReplicationExec(ctx, tablet.Tablet, query)
s.vexecPool.Release()

if err != nil {
return nil, err
}
Expand Down