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REP-6766 Compare documents using a batch cursor #148

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Merged
merged 10 commits into from
Oct 31, 2025
Merged

REP-6766 Compare documents using a batch cursor #148

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f1674d2
Rewrite compare to use batch cursor
FGasper Oct 29, 2025
ae55af2
fix testing
FGasper Oct 29, 2025
fd568f0
tweaks
FGasper Oct 29, 2025
e6f34e2
doc
FGasper Oct 29, 2025
e7841f4
more commenst
FGasper Oct 29, 2025
dc91802
comment
FGasper Oct 30, 2025
77de934
Merge branch 'main' into REP-6766-batch-cursor-compare
FGasper Oct 31, 2025
945ada3
gotta use raw after all
FGasper Oct 31, 2025
1e8c16f
no Must
FGasper Oct 31, 2025
dfcdc05
comments & rename
FGasper Oct 31, 2025
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163 changes: 111 additions & 52 deletions internal/verifier/compare.go
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@ import (
"bytes"
"context"
"fmt"
"iter"
"time"

"github.com/10gen/migration-verifier/chanutil"
Expand All @@ -12,6 +13,7 @@ import (
"github.com/10gen/migration-verifier/internal/retry"
"github.com/10gen/migration-verifier/internal/types"
"github.com/10gen/migration-verifier/internal/util"
"github.com/10gen/migration-verifier/mmongo/cursor"
"github.com/10gen/migration-verifier/option"
"github.com/pkg/errors"
"go.mongodb.org/mongo-driver/v2/bson"
Expand All @@ -30,6 +32,11 @@ const (
docKeyInHashedCompare = "k"
)

type seqWithTs struct {
seq iter.Seq2[bson.Raw, error]
ts bson.Timestamp
}

type docWithTs struct {
doc bson.Raw
ts bson.Timestamp
Expand All @@ -45,7 +52,7 @@ func (verifier *Verifier) FetchAndCompareDocuments(
types.ByteCount,
error,
) {
var srcChannel, dstChannel <-chan docWithTs
var srcChannel, dstChannel <-chan seqWithTs
var readSrcCallback, readDstCallback func(context.Context, *retry.FuncInfo) error

results := []VerificationResult{}
Expand Down Expand Up @@ -100,7 +107,7 @@ func (verifier *Verifier) compareDocsFromChannels(
workerNum int,
fi *retry.FuncInfo,
task *VerificationTask,
srcChannel, dstChannel <-chan docWithTs,
srcChannel, dstChannel <-chan seqWithTs,
) (
[]VerificationResult,
types.DocumentCount,
Expand Down Expand Up @@ -204,7 +211,7 @@ func (verifier *Verifier) compareDocsFromChannels(
for !srcClosed || !dstClosed {
simpleTimerReset(readTimer, readTimeout)

var srcDocWithTs, dstDocWithTs docWithTs
var srcDocsWithTs, dstDocsWithTs seqWithTs

eg, egCtx := contextplus.ErrGroup(ctx)

Expand All @@ -219,21 +226,13 @@ func (verifier *Verifier) compareDocsFromChannels(
"failed to read from source after %s",
readTimeout,
)
case srcDocWithTs, alive = <-srcChannel:
case srcDocsWithTs, alive = <-srcChannel:
if !alive {
srcClosed = true
break
}

fi.NoteSuccess("received document from source")

srcDocCount++
srcByteCount += types.ByteCount(len(srcDocWithTs.doc))
verifier.workerTracker.SetSrcCounts(
workerNum,
srcDocCount,
srcByteCount,
)
}

return nil
Expand All @@ -251,7 +250,7 @@ func (verifier *Verifier) compareDocsFromChannels(
"failed to read from destination after %s",
readTimeout,
)
case dstDocWithTs, alive = <-dstChannel:
case dstDocsWithTs, alive = <-dstChannel:
if !alive {
dstClosed = true
break
Expand All @@ -271,32 +270,72 @@ func (verifier *Verifier) compareDocsFromChannels(
)
}

if srcDocWithTs.doc != nil {
err := handleNewDoc(srcDocWithTs, true)
if srcDocsWithTs.seq != nil {
for doc, err := range srcDocsWithTs.seq {
if err != nil {
return nil, 0, 0, errors.Wrapf(
err,
"reading batch of docs from source (task: %s)",
task.PrimaryKey,
)
}

if err != nil {
srcDocCount++
srcByteCount += types.ByteCount(len(doc))
verifier.workerTracker.SetSrcCounts(
workerNum,
srcDocCount,
srcByteCount,
)

return nil, 0, 0, errors.Wrapf(
err,
"comparer thread failed to handle %#q's source doc (task: %s) with ID %v",
namespace,
task.PrimaryKey,
srcDocWithTs.doc.Lookup("_id"),
err := handleNewDoc(
docWithTs{
doc: doc,
ts: srcDocsWithTs.ts,
},
true,
)

if err != nil {
return nil, 0, 0, errors.Wrapf(
err,
"comparer thread failed to handle %#q's source doc (task: %s) with ID %v",
namespace,
task.PrimaryKey,
doc.Lookup("_id"),
)
}
}

}

if dstDocWithTs.doc != nil {
err := handleNewDoc(dstDocWithTs, false)
if dstDocsWithTs.seq != nil {
for doc, err := range dstDocsWithTs.seq {
if err != nil {
return nil, 0, 0, errors.Wrapf(
err,
"reading batch of docs from destination (task: %s)",
task.PrimaryKey,
)
}

if err != nil {
return nil, 0, 0, errors.Wrapf(
err,
"comparer thread failed to handle %#q's destination doc (task: %s) with ID %v",
namespace,
task.PrimaryKey,
dstDocWithTs.doc.Lookup("_id"),
err := handleNewDoc(
docWithTs{
doc: doc,
ts: dstDocsWithTs.ts,
},
false,
)

if err != nil {
return nil, 0, 0, errors.Wrapf(
err,
"comparer thread failed to handle %#q's destination doc (task: %s) with ID %v",
namespace,
task.PrimaryKey,
doc.Lookup("_id"),
)
}
}
}
}
Expand Down Expand Up @@ -427,13 +466,13 @@ func simpleTimerReset(t *time.Timer, dur time.Duration) {
func (verifier *Verifier) getFetcherChannelsAndCallbacks(
task *VerificationTask,
) (
<-chan docWithTs,
<-chan docWithTs,
<-chan seqWithTs,
<-chan seqWithTs,
func(context.Context, *retry.FuncInfo) error,
func(context.Context, *retry.FuncInfo) error,
) {
srcChannel := make(chan docWithTs)
dstChannel := make(chan docWithTs)
srcChannel := make(chan seqWithTs)
dstChannel := make(chan seqWithTs)

readSrcCallback := func(ctx context.Context, state *retry.FuncInfo) error {
// We open a session here so that we can read the session’s cluster
Expand Down Expand Up @@ -510,38 +549,44 @@ func (verifier *Verifier) getFetcherChannelsAndCallbacks(
}

func iterateCursorToChannel(
sctx context.Context,
ctx context.Context,
state *retry.FuncInfo,
cursor *mongo.Cursor,
writer chan<- docWithTs,
myCursor *cursor.BatchCursor,
writer chan<- seqWithTs,
) error {
defer close(writer)

sess := mongo.SessionFromContext(sctx)
for {
seq := myCursor.GetCurrentBatchIterator()

for cursor.Next(sctx) {
state.NoteSuccess("received a document")

clusterTime, err := util.GetClusterTimeFromSession(sess)
ct, err := myCursor.GetClusterTime()
if err != nil {
return errors.Wrap(err, "reading cluster time from session")
return errors.Wrap(err, "reading cluster time from batch")
}

err = chanutil.WriteWithDoneCheck(
sctx,
ctx,
writer,
docWithTs{
doc: slices.Clone(cursor.Current),
ts: clusterTime,
seqWithTs{
seq: seq,
ts: ct,
},
)

if err != nil {
return errors.Wrapf(err, "sending document to compare thread")
return errors.Wrapf(err, "sending iterator to compare thread")
}

if myCursor.IsFinished() {
return nil
}
}

return errors.Wrap(cursor.Err(), "failed to iterate cursor")
if err := myCursor.GetNext(ctx); err != nil {
return errors.Wrap(err, "failed to iterate cursor")
}
}
}

func getMapKey(docKeyValues []bson.RawValue) string {
Expand All @@ -555,8 +600,13 @@ func getMapKey(docKeyValues []bson.RawValue) string {
return keyBuffer.String()
}

func (verifier *Verifier) getDocumentsCursor(ctx context.Context, collection *mongo.Collection, clusterInfo *util.ClusterInfo,
startAtTs *bson.Timestamp, task *VerificationTask) (*mongo.Cursor, error) {
func (verifier *Verifier) getDocumentsCursor(
ctx context.Context,
collection *mongo.Collection,
clusterInfo *util.ClusterInfo,
startAtTs *bson.Timestamp,
task *VerificationTask,
) (*cursor.BatchCursor, error) {
var findOptions bson.D
runCommandOptions := options.RunCmd()
var andPredicates bson.A
Expand Down Expand Up @@ -673,7 +723,16 @@ func (verifier *Verifier) getDocumentsCursor(ctx context.Context, collection *mo
}
}

return collection.Database().RunCommandCursor(ctx, cmd, runCommandOptions)
c, err := cursor.New(
collection.Database(),
collection.Database().RunCommand(ctx, cmd, runCommandOptions),
)

if err == nil {
c.SetSession(mongo.SessionFromContext(ctx))
}
Comment on lines +731 to +733
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@tdq45gj tdq45gj Oct 31, 2025

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Is there a reason why SetSession is exported and called in the verifier code? Can we set the session in the cursor constructor?

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@FGasper FGasper Oct 31, 2025

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I had it that way for a bit, but then we’d need 2 constructors (one with a session & the other without).

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@FGasper FGasper Oct 31, 2025

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I’m starting to wonder, though, if it should always require a session. The driver does some funny-business under the hood to ensure that cursors always send the same LSID as the initial request.


return c, err
}

func transformPipelineForToHashedIndexKey(
Expand Down
13 changes: 8 additions & 5 deletions internal/verifier/migration_verifier_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@ import (
"github.com/10gen/migration-verifier/internal/types"
"github.com/10gen/migration-verifier/internal/util"
"github.com/10gen/migration-verifier/mbson"
"github.com/10gen/migration-verifier/mseq"
"github.com/10gen/migration-verifier/mslices"
"github.com/cespare/permute/v2"
"github.com/rs/zerolog"
Expand Down Expand Up @@ -1150,13 +1151,15 @@ func TestVerifierCompareDocs(t *testing.T) {

namespace := "testdb.testns"

makeDocChannel := func(docs []bson.D) <-chan docWithTs {
theChan := make(chan docWithTs, len(docs))
makeDocChannel := func(docs []bson.D) <-chan seqWithTs {
theChan := make(chan seqWithTs, len(docs))

for d, doc := range docs {
theChan <- docWithTs{
doc: testutil.MustMarshal(doc),
ts: bson.Timestamp{1, uint32(d)},
theChan <- seqWithTs{
seq: mseq.FromSliceWithNilErr(
mslices.Of(testutil.MustMarshal(doc)),
),
ts: bson.Timestamp{1, uint32(d)},
}
}

Expand Down
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