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1 .MongoDB cool administration tips
Gabriel Ciciliani - Percona Live Europe 2018
2 .#1 db.currentOps() flat output
3 .db.currentOps() flat output
mongo> db. currentOp(<filters>).inprog.forEach(
function(d){
var q = {};
print('ConnectionId: '+d.connectionId
+' Operation: '+d.op
+' Namespace: '+d.ns
+' Client:'+d.client
+' Seconds_running: '+d.secs_running
+' NumYields: '+d.numYields
+' Query:'+JSON.stringify (d.command))
}
)
Filters: {"ns":/^customers\./,"op":"insert","secs_running":{$gt:60}}
4 .db.currentOps() flat output
ConnectionId:88 Operation:command Namespace:sbtest.$cmd Client:172.19.0.1:59782 Seconds_running:53 NumYields:0
Query:{"createIndexes":"sbtest3","indexes":[{"name":"k_1","ns":"sbtest.sbtest3","background":false,"key":{"k":1}}],"$db":"sbtest"}
ConnectionId:86 Operation:command Namespace:sbtest.$cmd Client:172.19.0.1:59774 Seconds_running:53 NumYields:0
Query:{"createIndexes":"sbtest1","indexes":[{"name":"k_1","ns":"sbtest.sbtest1","background":false,"key":{"k":1}}],"$db":"sbtest"}
ConnectionId:87 Operation:command Namespace:sbtest.$cmd Client:172.19.0.1:59778 Seconds_running:53 NumYields:0
Query:{"createIndexes":"sbtest2","indexes":[{"name":"k_1","ns":"sbtest.sbtest2","background":false,"key":{"k":1}}],"$db":"sbtest"}
6 .Massive document update / removal
If the condition retrieves too many documents or there is no index
for the condition key:
● Determine lowest and highest _id for the condition specified
● Split the above range in fixed size chunks, by storing the chunk’s
boundaries in a list.
● Iterate through the chunks and execute the update operation for each
one
7 .Massive document removal
If the condition key is indexed
● use limit(), specify a chunksize and a delay. Iterate until no
documents matching the condition are found
8 .Database drop
● db.dropDatabase() requires a global write lock, blocking
other operations until it has completed.
● db.collection.drop() only requires a database level lock
● Drop all collections first, then drop the database
10 .Plan Cache Filters
db.runCommand(
{
planCacheSetFilter: <collection>,
query: <query>,
sort: <sort>,
projection: <projection>,
indexes: [ <index1>, <index2>, ...]
}
)
* query + sort + projection = query shape
11 .Unused Indexes
● db.orders.aggregate( [ { $indexStats: { } } ] )
...
"host" : "myhost:30008",
"accesses" : {
"ops" : NumberLong(4),
"since" : ISODate("2018-07-25T10:12:59.106Z")
}
...
● Needs to be executed for each collection => script!
12 .mtools
Written in python. For when the profiler is disabled.
● mlogfilter
○ --operation OP
○ --pattern P
○ --slow MS
○ --scan
○ --from FROM --to TO
● mplotqueries
14 .#4 SSL troubleshooting
15 .SSL troubleshooting
## Validate certificate - PK correspondence
$ openssl rsa -in mongo.key -noout -modulus | openssl md5
(stdin)= 45921d92f81d32ce48f02bcd904bdfb3
$ openssl x509 -in mongo.crt -noout -modulus | openssl md5
(stdin)= 45921d92f81d32ce48f02bcd904bdfb3
## Verifying alternate DNS names within the certificate
$ openssl x509 -in mongo.crt -text | grep DNS
## Verifying certificate against the CA certificates
$ openssl verify -CAfile /etc/ssl/mongo-rootAndChain.crt /etc/ssl/server.pem
/etc/ssl/server.pem: OK
16 .SSL troubleshooting
## Configuration
ssl:
mode:[ allowSSL | preferSSL | requireSSL | ]
allowConnectionsWithoutCertificates: true
17 .#5 Replicasets and Sharding
18 .Sharded clusters maintenance
● Dealing with Jumbo chunks
○ Divide the chunk using sh.splitAt()
○ Manually clear the flag updating config.chunks
● Remember that explain()can be used to verify chunk migration
operations
● Update mongoS cache after a manual chunks migration, clearing a jumbo
chunk flag, removing a shard or issuing movePrimary
○ db.adminCommand({ flushRouterConfig: 1 } )
● Query config.mongos to obtain a list of mongoS nodes that ever
connected to the cluster. Useful when migrating config servers
19 .Preventing cross-region traffic
● Hide a replicaset member to make it invisible to
applications
● Use tags to prioritize traffic on one region over the
other
>>> from pymongo.read_preferences import Secondary
>>> db = client.get_database(
... 'test', read_preference=Secondary([{'dc': 'ny'}, {'dc': 'sf'}]))
20 .Example scripts
Example script to process updates in chunks
https://github.com/gabocic/mongodb/blob/master/chunksfinder.js
Example to drop a database by dropping all collections first
https://github.com/gabocic/mongodb/blob/master/dropDatabasesLowImpact.js
Simple collection pruning example
https://github.com/gabocic/mongodb/blob/master/simpleCollectionPruning.js
Full collection pruning example including emergency halt and logging
https://github.com/gabocic/mongodb/blob/master/pruneDropCollections.js
Flat currentOps()
https://github.com/gabocic/mongodb/blob/master/flatcurrentops.js
Unused indexes
https://github.com/gabocic/mongodb/blob/master/unusedidx.js
21 . Thanks!
Gabriel Ciciliani
ciciliani@pythian.com
www.linkedin.com/in/gabrielciciliani
@gabocic
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