Copy Set Principle
The role of replication sets
In order to achieve high availability of mongodb services, there is a master-slave relationship between replica sets
- Quickly copy data to other nodes when data is written
- Automatically select a new node to replace the primary node when it fails
With the above features, if we know redis, we can quickly associate Sentinel mode
In addition to the above two major features of data synchronization and fault node substitution, replication sets have the following roles
Data distribution: Distribute data to different areas to reduce latency in reading
For example, the company has data centers in Beijing, Shanghai and Guangzhou, but only Beijing is a writable center, which can distribute data in different places to improve the reading efficiency of users in Shanghai and Guangzhou.
- Read-Write Separation
- Disaster tolerance in different places: Switch to different places quickly when the data center fails.
The structure of the replica set
The structure of the replica set is similar to that of other middleware.
A typical replica set consists of three or more nodes with votes:
- Primary node: There is only one, responsible for writing and reading data, and voting during elections.
- From Node: There are at least two responsible for data reading and voting.
Principle of data replication
- When the data (primary node) is modified (added or deleted), its operations on the data are recorded in an oplog file.
- Consistent with the data on the primary node, the slave node continuously obtains new oplog s from the primary node by opening a tailable cursor on the primary node and reproduces these operations on its own node.
Principle of primary node election
- Two or two nodes with voting rights send heartbeats to each other.
- Nodes are disconnected when five heartbeats are not received.
- If the primary node is disconnected, a new primary node is selected from the secondary node, but the disconnected secondary node will not participate in the election.
- Elections are based on the RAFT consistency algorithm, and the necessary condition for a successful election is that most voting nodes survive.
- A replica set can have up to 50 nodes, but a maximum of 7 nodes with voting rights.
- Nodes selected as primary nodes must be able to establish connections with most nodes, have newer oplog s, have higher priority (if any in the configuration)
Build a replica set
Here's how to create a mongodb replica set under linux
Create three directories
mkdir -p /data/mongodb/db{1,2,3}configuration file
#Node 1 systemLog: destination: file path: /data/mongodb/db1/mongod.log #Log Path logAppend: true storage: dbPath: /data/mongodb/db1 #data file net: bindIp: 0.0.0.0 #Listen on all network cards for external network access port: 28017 replication: #Copy set, if not a single node replSetName: rs0 #Copy Set Name processManagement: fork: true #Make the process a stand-alone background process #Node 2 systemLog: destination: file path: /data/mongodb/db2/mongod.log #Log Path logAppend: true storage: dbPath: /data/mongodb/db2 #data file net: bindIp: 0.0.0.0 #Listen on all network cards for external network access port: 28018 replication: #Copy set, if not a single node replSetName: rs0 #Copy Set Name processManagement: fork: true #Make the process a stand-alone background process #Node 3 systemLog: destination: file path: /data/mongodb/db3/mongod.log #Log Path logAppend: true storage: dbPath: /data/mongodb/db3 #data file net: bindIp: 0.0.0.0 #Listen on all network cards for external network access port: 28019 replication: #Copy set, if not a single node replSetName: rs0 #Copy Set Name processManagement: fork: true #Make the process a stand-alone background process
Start process
mongod -f db1/mongod.conf mongod -f db2/mongod.conf mongod -f db3/mongod.conf
Configure replica sets
Enter the primary node
mongo --port 28017
Set Primary Node
rs.initiate()
{ "info2" : "no configuration specified. Using a default configuration for the set", "me" : "supman:28017", "ok" : 1 }View node status
rs.status()
{ "set" : "rs0", "date" : ISODate("2021-11-30T15:33:30.616Z"), "myState" : 1, "term" : NumberLong(1), "syncSourceHost" : "", "syncSourceId" : -1, "heartbeatIntervalMillis" : NumberLong(2000), "majorityVoteCount" : 1, "writeMajorityCount" : 1, "votingMembersCount" : 1, "writableVotingMembersCount" : 1, "optimes" : { "lastCommittedOpTime" : { "ts" : Timestamp(1638286404, 1), "t" : NumberLong(1) }, "lastCommittedWallTime" : ISODate("2021-11-30T15:33:24.656Z"), "readConcernMajorityOpTime" : { "ts" : Timestamp(1638286404, 1), "t" : NumberLong(1) }, "readConcernMajorityWallTime" : ISODate("2021-11-30T15:33:24.656Z"), "appliedOpTime" : { "ts" : Timestamp(1638286404, 1), "t" : NumberLong(1) }, "durableOpTime" : { "ts" : Timestamp(1638286404, 1), "t" : NumberLong(1) }, "lastAppliedWallTime" : ISODate("2021-11-30T15:33:24.656Z"), "lastDurableWallTime" : ISODate("2021-11-30T15:33:24.656Z") }, "lastStableRecoveryTimestamp" : Timestamp(1638286364, 1), "electionCandidateMetrics" : { "lastElectionReason" : "electionTimeout", "lastElectionDate" : ISODate("2021-11-30T15:27:54.614Z"), "electionTerm" : NumberLong(1), "lastCommittedOpTimeAtElection" : { "ts" : Timestamp(0, 0), "t" : NumberLong(-1) }, "lastSeenOpTimeAtElection" : { "ts" : Timestamp(1638286074, 1), "t" : NumberLong(-1) }, "numVotesNeeded" : 1, "priorityAtElection" : 1, "electionTimeoutMillis" : NumberLong(10000), "newTermStartDate" : ISODate("2021-11-30T15:27:54.637Z"), "wMajorityWriteAvailabilityDate" : ISODate("2021-11-30T15:27:54.660Z") }, "members" : [ { "_id" : 0, "name" : "supman:28017", "health" : 1, "state" : 1, "stateStr" : "PRIMARY", "uptime" : 1227, "optime" : { "ts" : Timestamp(1638286404, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2021-11-30T15:33:24Z"), "syncSourceHost" : "", "syncSourceId" : -1, "infoMessage" : "", "electionTime" : Timestamp(1638286074, 2), "electionDate" : ISODate("2021-11-30T15:27:54Z"), "configVersion" : 1, "configTerm" : 1, "self" : true, "lastHeartbeatMessage" : "" } ], "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1638286404, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1638286404, 1) }Find the members.name field in the status information
"name" : "supman:28017"
Add slave node
rs.add("supman:28018")
{ "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1638286626, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1638286626, 1) }rs.add("supman:28019")
{ "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1638286660, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1638286660, 1) }View status again
{ "set" : "rs0", "date" : ISODate("2021-11-30T15:44:29.903Z"), "myState" : 1, "term" : NumberLong(1), "syncSourceHost" : "", "syncSourceId" : -1, "heartbeatIntervalMillis" : NumberLong(2000), "majorityVoteCount" : 2, "writeMajorityCount" : 2, "votingMembersCount" : 3, "writableVotingMembersCount" : 3, "optimes" : { "lastCommittedOpTime" : { "ts" : Timestamp(1638287064, 1), "t" : NumberLong(1) }, "lastCommittedWallTime" : ISODate("2021-11-30T15:44:24.673Z"), "readConcernMajorityOpTime" : { "ts" : Timestamp(1638287064, 1), "t" : NumberLong(1) }, "readConcernMajorityWallTime" : ISODate("2021-11-30T15:44:24.673Z"), "appliedOpTime" : { "ts" : Timestamp(1638287064, 1), "t" : NumberLong(1) }, "durableOpTime" : { "ts" : Timestamp(1638287064, 1), "t" : NumberLong(1) }, "lastAppliedWallTime" : ISODate("2021-11-30T15:44:24.673Z"), "lastDurableWallTime" : ISODate("2021-11-30T15:44:24.673Z") }, "lastStableRecoveryTimestamp" : Timestamp(1638287034, 1), "electionCandidateMetrics" : { "lastElectionReason" : "electionTimeout", "lastElectionDate" : ISODate("2021-11-30T15:27:54.614Z"), "electionTerm" : NumberLong(1), "lastCommittedOpTimeAtElection" : { "ts" : Timestamp(0, 0), "t" : NumberLong(-1) }, "lastSeenOpTimeAtElection" : { "ts" : Timestamp(1638286074, 1), "t" : NumberLong(-1) }, "numVotesNeeded" : 1, "priorityAtElection" : 1, "electionTimeoutMillis" : NumberLong(10000), "newTermStartDate" : ISODate("2021-11-30T15:27:54.637Z"), "wMajorityWriteAvailabilityDate" : ISODate("2021-11-30T15:27:54.660Z") }, "members" : [ { "_id" : 0, "name" : "supman:28017", "health" : 1, "state" : 1, "stateStr" : "PRIMARY", "uptime" : 1886, "optime" : { "ts" : Timestamp(1638287064, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2021-11-30T15:44:24Z"), "syncSourceHost" : "", "syncSourceId" : -1, "infoMessage" : "", "electionTime" : Timestamp(1638286074, 2), "electionDate" : ISODate("2021-11-30T15:27:54Z"), "configVersion" : 3, "configTerm" : 1, "self" : true, "lastHeartbeatMessage" : "" }, { "_id" : 1, "name" : "supman:28018", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 442, "optime" : { "ts" : Timestamp(1638287064, 1), "t" : NumberLong(1) }, "optimeDurable" : { "ts" : Timestamp(1638287064, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2021-11-30T15:44:24Z"), "optimeDurableDate" : ISODate("2021-11-30T15:44:24Z"), "lastHeartbeat" : ISODate("2021-11-30T15:44:28.545Z"), "lastHeartbeatRecv" : ISODate("2021-11-30T15:44:28.566Z"), "pingMs" : NumberLong(0), "lastHeartbeatMessage" : "", "syncSourceHost" : "supman:28017", "syncSourceId" : 0, "infoMessage" : "", "configVersion" : 3, "configTerm" : 1 }, { "_id" : 2, "name" : "supman:28019", "health" : 1, "state" : 2, "stateStr" : "SECONDARY", "uptime" : 409, "optime" : { "ts" : Timestamp(1638287064, 1), "t" : NumberLong(1) }, "optimeDurable" : { "ts" : Timestamp(1638287064, 1), "t" : NumberLong(1) }, "optimeDate" : ISODate("2021-11-30T15:44:24Z"), "optimeDurableDate" : ISODate("2021-11-30T15:44:24Z"), "lastHeartbeat" : ISODate("2021-11-30T15:44:28.565Z"), "lastHeartbeatRecv" : ISODate("2021-11-30T15:44:29.316Z"), "pingMs" : NumberLong(0), "lastHeartbeatMessage" : "", "syncSourceHost" : "supman:28018", "syncSourceId" : 1, "infoMessage" : "", "configVersion" : 3, "configTerm" : 1 } ], "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1638287064, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1638287064, 1) }Configure Readable from Node
Enter From Node
mongo --port 28018 mongo --port 28019
Set Readable From Node
rs.slaveOk()
- Finally, add a user to the primary node, create a database and collection, and view the data from the node after inserting the data