mongodb

Connect with mongosh Open interactive shell to a MongoDB instance mongosh 'mongodb://user:pass@mongo:27017/dbname' #mongodb Replica set status Show replica set members, lag, and election status mongosh --eval 'rs.status()' mongodb://mongo:27017 #mongodb#monitoring Database stats Data size, storage size, collection count for a database mongosh --eval 'db.stats()' mongodb://mongo:27017/mydb #mongodb#monitoring Collection stats Document count, index sizes, storage for a collection mongosh --eval 'db.myCollection.stats()' mongodb://mongo:27017/mydb #mongodb Current operations Show operations running longer than 5 seconds mongosh --eval 'db.currentOp({active:true,secs_running:{$gt:5}})' mongodb://mongo:27017 #mongodb#debug#monitoring Create dump Export database to BSON files mongodump --uri='mongodb://user:pass@mongo:27017' --db=mydb --out=/backups/ #mongodb Restore dump Import BSON backup into MongoDB mongorestore --uri='mongodb://user:pass@mongo:27017' --db=mydb /backups/mydb/ #mongodb List indexes Show all indexes on a collection mongosh --eval 'db.myCollection.getIndexes()' mongodb://mongo:27017/mydb #mongodb Connect with URI Connect to Atlas or any MongoDB URI with mongosh mongosh 'mongodb+srv://user:pass@cluster.example.com/mydb' #mongodb Explain query plan Show execution stats including index usage db.orders.find({status:'new'}).explain('executionStats') #mongodb#debug Create compound index Ascending userId + descending createdAt index db.orders.createIndex({userId: 1, createdAt: -1}, {background: true}) #mongodb Aggregation pipeline example Top 10 users by paid order amount db.orders.aggregate([{$match:{status:'paid'}},{$group:{_id:'$userId',total:{$sum:'$amount'}}},{$sort:{total:-1}},{$limit:10}]) #mongodb Check replication lag Show secondary lag and oplog window rs.printSecondaryReplicationInfo() #mongodb#monitoring Current operations (slow queries) List operations running longer than 5 seconds db.currentOp({active:true, secs_running:{$gt:5}}) #mongodb#debug Dump a database Dump all collections in a database to BSON files mongodump --uri='mongodb://localhost:27017' --db=mydb --out=/backup/$(date +%F) #mongodb Replica set status Per-member state and last applied optime; spot lagging or unhealthy secondaries mongosh --eval 'rs.status().members.forEach(m=>print(m.name,m.stateStr,m.optimeDate))' #mongodb#monitoring#troubleshooting#observability Kill long-running ops List queries running >5s with ns then killOp each; note: killOp is async, verify after mongosh --eval 'db.currentOp({secs_running:{$gt:5},op:{$ne:"none"}}).inprog.forEach(o=>{print(o.opid,o.secs_running,o.ns); db.killOp(o.opid)})' #mongodb#troubleshooting#performance#debug Query plan with stats Show docs examined vs returned and index usage; COLLSCAN means missing index mongosh --eval 'db.<name>.find({status:"active"}).explain("executionStats").executionStats' #mongodb#performance#troubleshooting#debug Unused index detection Access count per index; zero ops = candidate to drop and reclaim write cost mongosh --eval 'db.<name>.aggregate([{$indexStats:{}}]).forEach(i=>print(i.name,i.accesses.ops))' #mongodb#performance#disk#monitoring Profile slow queries Capture ops slower than 100ms then read top offenders from system.profile mongosh --eval 'db.setProfilingLevel(1,{slowms:100}); db.system.profile.find().sort({millis:-1}).limit(5)' #mongodb#performance#troubleshooting#observability