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Type: Bug
Resolution: Unresolved
Priority: Major - P3
Fix Version/s: None
Affects Version/s: 8.0.28
Component/s: None
Labels:
None

Operating System:
ALL
Steps To Reproduce:

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8.0.28:-- no longer returns results and gets stuck.
[direct: mongos] outMonitor> db.monitorOut.count({ct:{$gte:ISODate("2026-08-19T00:00:00"),$lt:ISODate("2026-08-20T00:00:00")}})
DeprecationWarning: Collection.count() is deprecated. Use countDocuments or estimatedDocumentCount.
wait 30m --can't return result
{
shard: 'shard7',
type: 'op',
desc: 'conn276941',
connectionId: 276941,
appName: 'mongosh 2.5.2',
clientMetadata: {
application:
{ name: 'mongosh 2.5.2' }
,
driver:
{ name: 'nodejs|mongosh', version: '6.16.0|2.5.2' }
,
platform: 'Node.js v20.19.2, LE',
os:
{ name: 'linux', architecture: 'x64', version: '3.10.0-327.22.2.el7.x86_64', type: 'Linux' }
,
mongos:
{ client: 'anonymous unix socket:27017', version: '8.0.28' }
},
active: true,
currentOpTime: '2026-09-02T11:54:26.500+08:00',
effectiveUsers: [
{ user: 'admin', db: 'admin' }
],
runBy: [
{ user: '__system', db: 'local' }
],
isFromUserConnection: true,
threaded: true,
opid: 'shard7:780952580',
lsid:
{ id: UUID('4e7e96f2-317a-49a0-a274-4585d5e531fe'), uid: Binary.createFromBase64('O0CMtIVItQN4IsEOsJdrPL8s7jv5xwh5a/A5Qfvs2A8=', 0) }
,
secs_running: Long('2717'),
microsecs_running: Long('2717087426'),
op: 'command',
ns: 'outMonitor.monitorOut',
redacted: false,
command: {
explain: {
find: 'monitorOut',
filter: {
ct:
{ '$gte': ISODate('2026-08-19T00:00:00.000Z'), '$lt': ISODate('2026-08-20T00:00:00.000Z') }
}
},
verbosity: 'executionStats',
readConcern:
{ level: 'local', provenance: 'implicitDefault' }
,
shardVersion: {
e: ObjectId('6a858b7c4bb33126ec6459ce'),
t: Timestamp(
{ t: 1787136892, i: 19 }
),
v: Timestamp(
{ t: 29706, i: 2 }
)
},
lsid:
{ id: UUID('4e7e96f2-317a-49a0-a274-4585d5e531fe'), uid: Binary.createFromBase64('O0CMtIVItQN4IsEOsJdrPL8s7jv5xwh5a/A5Qfvs2A8=', 0) }
,
'$clusterTime': { clusterTime: Timestamp(
{ t: 1788318544, i: 1 }
) },
'$configTime': Timestamp(
{ t: 1788318544, i: 1 }
),
'$topologyTime': Timestamp(
{ t: 1787014773, i: 10 }
),
'$audit': {
'$impersonatedUser':
{ user: 'admin', db: 'admin' }
,
'$impersonatedRoles': [
{ role: 'root', db: 'admin' }
]
},
'$client': {
application:
{ name: 'mongosh 2.5.2' }
,
driver:
{ name: 'nodejs|mongosh', version: '6.16.0|2.5.2' }
,
platform: 'Node.js v20.19.2, LE',
os:
{ name: 'linux', architecture: 'x64', version: '3.10.0-327.22.2.el7.x86_64', type: 'Linux' }
,
mongos:
{ host: 'srvmid1670.yto.cloud:21051', client: 'anonymous unix socket:27017', version: '8.0.28' }
},
mayBypassWriteBlocking: true,
'$db': 'outMonitor'
},
queryFramework: 'classic',
numYields: 16846,
numInterruptChecks: Long('33697'),
queues: {
execution:
{ admissions: 16847, totalTimeQueuedMicros: Long('0') }
,
ingress:
{ admissions: 1, totalTimeQueuedMicros: Long('0') }
},
currentQueue: null,
locks:
{ Global: 'r' }
,
waitingForLock: false,
lockStats: {
Global: { acquireCount:
{ r: Long('16847') }
},
Mutex: { acquireCount:
{ r: Long('3') }
}
},
waitingForFlowControl: false,
flowControlStats: {}
}

4.2.12:
mongos> db.monitorOut.count({ct:{$gte:ISODate("2026-08-19T00:00:00"),$lt:ISODate("2026-08-20T00:00:00")}})
86954105

5m can return result

Show
8.0.28:-- no longer returns results and gets stuck. [direct: mongos] outMonitor> db.monitorOut.count({ct:{$gte:ISODate("2026-08-19T00:00:00"),$lt:ISODate("2026-08-20T00:00:00")}}) DeprecationWarning: Collection.count() is deprecated. Use countDocuments or estimatedDocumentCount. wait 30m --can't return result { shard: 'shard7', type: 'op', desc: 'conn276941', connectionId: 276941, appName: 'mongosh 2.5.2', clientMetadata: { application: { name: 'mongosh 2.5.2' } , driver: { name: 'nodejs|mongosh', version: '6.16.0|2.5.2' } , platform: 'Node.js v20.19.2, LE', os: { name: 'linux', architecture: 'x64', version: '3.10.0-327.22.2.el7.x86_64', type: 'Linux' } , mongos: { client: 'anonymous unix socket:27017', version: '8.0.28' } }, active: true, currentOpTime: '2026-09-02T11:54:26.500+08:00', effectiveUsers: [ { user: 'admin', db: 'admin' } ], runBy: [ { user: '__system', db: 'local' } ], isFromUserConnection: true, threaded: true, opid: 'shard7:780952580', lsid: { id: UUID('4e7e96f2-317a-49a0-a274-4585d5e531fe'), uid: Binary.createFromBase64('O0CMtIVItQN4IsEOsJdrPL8s7jv5xwh5a/A5Qfvs2A8=', 0) } , secs_running: Long('2717'), microsecs_running: Long('2717087426'), op: 'command', ns: 'outMonitor.monitorOut', redacted: false, command: { explain: { find: 'monitorOut', filter: { ct: { '$gte': ISODate('2026-08-19T00:00:00.000Z'), '$lt': ISODate('2026-08-20T00:00:00.000Z') } } }, verbosity: 'executionStats', readConcern: { level: 'local', provenance: 'implicitDefault' } , shardVersion: { e: ObjectId('6a858b7c4bb33126ec6459ce'), t: Timestamp( { t: 1787136892, i: 19 } ), v: Timestamp( { t: 29706, i: 2 } ) }, lsid: { id: UUID('4e7e96f2-317a-49a0-a274-4585d5e531fe'), uid: Binary.createFromBase64('O0CMtIVItQN4IsEOsJdrPL8s7jv5xwh5a/A5Qfvs2A8=', 0) } , '$clusterTime': { clusterTime: Timestamp( { t: 1788318544, i: 1 } ) }, '$configTime': Timestamp( { t: 1788318544, i: 1 } ), '$topologyTime': Timestamp( { t: 1787014773, i: 10 } ), '$audit': { '$impersonatedUser': { user: 'admin', db: 'admin' } , '$impersonatedRoles': [ { role: 'root', db: 'admin' } ] }, '$client': { application: { name: 'mongosh 2.5.2' } , driver: { name: 'nodejs|mongosh', version: '6.16.0|2.5.2' } , platform: 'Node.js v20.19.2, LE', os: { name: 'linux', architecture: 'x64', version: '3.10.0-327.22.2.el7.x86_64', type: 'Linux' } , mongos: { host: 'srvmid1670.yto.cloud:21051', client: 'anonymous unix socket:27017', version: '8.0.28' } }, mayBypassWriteBlocking: true, '$db': 'outMonitor' }, queryFramework: 'classic', numYields: 16846, numInterruptChecks: Long('33697'), queues: { execution: { admissions: 16847, totalTimeQueuedMicros: Long('0') } , ingress: { admissions: 1, totalTimeQueuedMicros: Long('0') } }, currentQueue: null, locks: { Global: 'r' } , waitingForLock: false, lockStats: { Global: { acquireCount: { r: Long('16847') } }, Mutex: { acquireCount: { r: Long('3') } } }, waitingForFlowControl: false, flowControlStats: {} } 4.2.12: mongos> db.monitorOut.count({ct:{$gte:ISODate("2026-08-19T00:00:00"),$lt:ISODate("2026-08-20T00:00:00")}}) 86954105 5m can return result
CAR Domain/s:
None

Aha! Reference:
None
Tracking Level:
None
Risk Status:
None
Exec Notes:
None
Goal Name(s):
None
Goal Link:
None

After upgrading and expanding a sharded cluster from 6 shards on MongoDB 4.2 to 12 shards on MongoDB 8.0, a count query on a one-day time range no longer returns results and gets stuck. This query had been fast on the original 4.2 cluster. query using ct index。
db.monitorOut.count({ct:{$gte:ISODate("2026-08-19T00:00:00"),$lt:ISODate("2026-08-20T00:00:00")}})

is related to

SERVER-39191 Performance regression for counts post-sharding

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