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distsql: do not change concurrency for keep order request when @@tidb_distsql_scan_concurrency is set #60803

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Merged
merged 1 commit into from
May 16, 2025
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distsql: do not change concurrency for keep order request when @@tidb_distsql_scan_concurrency is set #60803

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8 changes: 6 additions & 2 deletions pkg/distsql/request_builder.go
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,7 @@ import (
"github.com/pingcap/tidb/pkg/kv"
"github.com/pingcap/tidb/pkg/meta/model"
"github.com/pingcap/tidb/pkg/parser/mysql"
"github.com/pingcap/tidb/pkg/sessionctx/vardef"
"github.com/pingcap/tidb/pkg/tablecodec"
"github.com/pingcap/tidb/pkg/types"
"github.com/pingcap/tidb/pkg/util/codec"
Expand Down Expand Up @@ -81,14 +82,17 @@ func (builder *RequestBuilder) Build() (*kv.Request, error) {

if dag := builder.dag; dag != nil {
if execCnt := len(dag.Executors); execCnt == 1 {
oldConcurrency := builder.Request.Concurrency
// select * from t order by id
if builder.Request.KeepOrder {
if builder.Request.KeepOrder && builder.Request.Concurrency == vardef.DefDistSQLScanConcurrency {
// When the DAG is just simple scan and keep order, set concurrency to 2.
// If a lot data are returned to client, mysql protocol is the bottleneck so concurrency 2 is enough.
// If very few data are returned to client, the speed is not optimal but good enough.
//
// If a user set @@tidb_distsql_scan_concurrency, he must be doing it by intention.
// so only rewrite concurrency when @@tidb_distsql_scan_concurrency is default value.
switch dag.Executors[0].Tp {
case tipb.ExecType_TypeTableScan, tipb.ExecType_TypeIndexScan, tipb.ExecType_TypePartitionTableScan:
oldConcurrency := builder.Request.Concurrency
builder.Request.Concurrency = 2
failpoint.Inject("testRateLimitActionMockConsumeAndAssert", func(val failpoint.Value) {
if val.(bool) {
Expand Down
8 changes: 8 additions & 0 deletions tests/integrationtest/r/executor/issues.result
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Expand Up @@ -1000,6 +1000,14 @@ Limit_11 1.00 <actRows> root NULL NULL offset:0, count:100 <memory> <disk>
└─Limit_19 1.00 <actRows> cop[tikv] NULL NULL offset:0, count:100 <memory> <disk>
└─Selection_18 1.00 <actRows> cop[tikv] NULL NULL eq(executor__issues.pt.val, 126) <memory> <disk>
└─TableFullScan_17 256.00 <actRows> cop[tikv] table:pt NULL keep order:true <memory> <disk>
explain analyze select /*+ set_var(tidb_distsql_scan_concurrency=5)*/ * from t order by id;
id estRows actRows task access object execution info operator info memory disk
TableReader_11 256.00 <actRows> root NULL max_distsql_concurrency: 5 NULL <memory> <disk>
└─TableFullScan_10 256.00 <actRows> cop[tikv] table:t NULL keep order:true <memory> <disk>
explain analyze select /*+ set_var(tidb_distsql_scan_concurrency=15)*/ * from t order by id;
id estRows actRows task access object execution info operator info memory disk
TableReader_11 256.00 <actRows> root NULL max_distsql_concurrency: 2 NULL <memory> <disk>
└─TableFullScan_10 256.00 <actRows> cop[tikv] table:t NULL keep order:true <memory> <disk>
CREATE TABLE test_55837 (col1 int(4) NOT NULL, col2 bigint(4) NOT NULL, KEY col2_index (col2));
insert into test_55837 values(0,1725292800),(0,1725292800);
select from_unixtime( if(col2 >9999999999, col2/1000, col2), '%Y-%m-%d %H:%i:%s') as result from test_55837;
Expand Down
9 changes: 9 additions & 0 deletions tests/integrationtest/t/executor/issues.test
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Expand Up @@ -763,6 +763,15 @@ explain analyze select * from pt order by id limit 100000; # expected dists
-- replace_regex /.*max_distsql_concurrency: (?P<num>[0-9]+).*/max_distsql_concurrency: $num/ /tikv_task:.*// /time:.*// /data:.*//
explain analyze select * from pt where val = 126 order by id limit 100; # expected distsql concurrency 15

-- replace_column 8 <memory> 9 <disk> 3 <actRows>
-- replace_regex /.*max_distsql_concurrency: (?P<num>[0-9]+).*/max_distsql_concurrency: $num/ /tikv_task:.*// /time:.*// /data:.*//
explain analyze select /*+ set_var(tidb_distsql_scan_concurrency=5)*/ * from t order by id; # expected distsql concurrency 5

-- replace_column 8 <memory> 9 <disk> 3 <actRows>
-- replace_regex /.*max_distsql_concurrency: (?P<num>[0-9]+).*/max_distsql_concurrency: $num/ /tikv_task:.*// /time:.*// /data:.*//
explain analyze select /*+ set_var(tidb_distsql_scan_concurrency=15)*/ * from t order by id; # expected distsql concurrency 2


# TestIssue55837
CREATE TABLE test_55837 (col1 int(4) NOT NULL, col2 bigint(4) NOT NULL, KEY col2_index (col2));
insert into test_55837 values(0,1725292800),(0,1725292800);
Expand Down