Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

kv: permit ExportRequest evaluation on followers #91405

Merged
merged 1 commit into from
Dec 7, 2022
Merged

kv: permit ExportRequest evaluation on followers #91405

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
27 changes: 22 additions & 5 deletions pkg/ccl/kvccl/kvfollowerreadsccl/followerreads_test.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -108,10 +108,12 @@ func TestCanSendToFollower(t *testing.T) {
txn.GlobalUncertaintyLimit = ts
return txn
}
batch := func(txn *roachpb.Transaction, req roachpb.Request) *roachpb.BatchRequest {
batch := func(txn *roachpb.Transaction, reqs ...roachpb.Request) *roachpb.BatchRequest {
ba := &roachpb.BatchRequest{}
ba.Txn = txn
ba.Add(req)
for _, req := range reqs {
ba.Add(req)
}
return ba
}
withBatchTimestamp := func(ba *roachpb.BatchRequest, ts hlc.Timestamp) *roachpb.BatchRequest {
Expand Down Expand Up @@ -146,7 +148,17 @@ func TestCanSendToFollower(t *testing.T) {
{
name: "stale non-txn export batch",
ba: withBatchTimestamp(batch(nil, &roachpb.ExportRequest{}), stale),
exp: false,
exp: true,
},
{
name: "stale non-txn multiple exports batch",
ba: withBatchTimestamp(batch(nil, &roachpb.ExportRequest{}, &roachpb.ExportRequest{}), stale),
exp: true,
},
{
name: "stale non-txn mixed export-scan batch",
ba: withBatchTimestamp(batch(nil, &roachpb.ExportRequest{}, &roachpb.ScanRequest{}), stale),
exp: true,
},
{
name: "current-time non-txn batch",
Expand All @@ -158,6 +170,11 @@ func TestCanSendToFollower(t *testing.T) {
ba: withBatchTimestamp(batch(nil, &roachpb.ExportRequest{}), current),
exp: false,
},
{
name: "current-time non-txn multiple exports batch",
ba: withBatchTimestamp(batch(nil, &roachpb.ExportRequest{}, &roachpb.ExportRequest{}), current),
exp: false,
},
{
name: "future non-txn batch",
ba: withBatchTimestamp(batch(nil, &roachpb.GetRequest{}), future),
Expand Down Expand Up @@ -275,7 +292,7 @@ func TestCanSendToFollower(t *testing.T) {
name: "stale non-txn export batch, global reads policy",
ba: withBatchTimestamp(batch(nil, &roachpb.ExportRequest{}), stale),
ctPolicy: roachpb.LEAD_FOR_GLOBAL_READS,
exp: false,
exp: true,
},
{
name: "current-time non-txn batch, global reads policy",
Expand All @@ -287,7 +304,7 @@ func TestCanSendToFollower(t *testing.T) {
name: "current-time non-txn export batch, global reads policy",
ba: withBatchTimestamp(batch(nil, &roachpb.ExportRequest{}), current),
ctPolicy: roachpb.LEAD_FOR_GLOBAL_READS,
exp: false,
exp: true,
},
{
name: "future non-txn batch, global reads policy",
Expand Down
49 changes: 35 additions & 14 deletions pkg/kv/kvserver/replica_follower_read.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -37,24 +37,45 @@ var FollowerReadsEnabled = settings.RegisterBoolSetting(
// requests that can be evaluated on a follower replica, given a sufficiently
// advanced closed timestamp.
func BatchCanBeEvaluatedOnFollower(ba *roachpb.BatchRequest) bool {
// Explanation of conditions:
// 1. the batch cannot have or intend to receive a timestamp set from a
// server-side clock. If a follower with a lagging clock sets its timestamp
// and this then allows the follower to evaluate the batch as a follower
// read, then the batch might miss past writes served at higher timestamps
// on the leaseholder.
// 2. each request in the batch needs to be "transactional", because those are
// the only ones that have clearly defined semantics when served under the
// closed timestamp.
// 3. the batch needs to be read-only, because a follower replica cannot
// propose writes to Raft.
// 4. the batch needs to be non-locking, because unreplicated locks are only
// held on the leaseholder.
// Various restrictions apply to a batch for it to be successfully considered
// for evaluation on a follower replica, which are described inline.
//
// The batch cannot have or intend to receive a timestamp set from a
// server-side clock. If follower with a lagging clock sets its timestamp
// and this then allows the follower to evaluate the batch as a follower read,
// then the batch might miss past writes served at higher timestamps on the
// leaseholder.
tsFromServerClock := ba.Txn == nil && (ba.Timestamp.IsEmpty() || ba.TimestampFromServerClock != nil)
if tsFromServerClock {
return false
}
return ba.IsAllTransactional() && ba.IsReadOnly() && !ba.IsLocking()
if len(ba.Requests) == 0 {
// No requests to evaluate.
return false
}
// Each request in the batch needs to have clearly defined semantics when
// served under the closed timestamp.
for _, ru := range ba.Requests {
r := ru.GetInner()
switch {
case roachpb.IsTransactional(r):
// Transactional requests have clear semantics when served under the
// closed timestamp. The request must be read-only, as follower replicas
// cannot propose writes to Raft. The request also needs to be
// non-locking, because unreplicated locks are only held on the
// leaseholder.
if !roachpb.IsReadOnly(r) || roachpb.IsLocking(r) {
return false
}
case r.Method() == roachpb.Export:
// Export requests also have clear semantics when served under the closed
// timestamp as well, even though they are non-transactional, as they
// define the start and end timestamp to export data over.
default:
return false
}
}
return true
}

// canServeFollowerReadRLocked tests, when a range lease could not be acquired,
Expand Down