Setting up replication

Manticore can replicate a write transaction (INSERT, REPLACE, DELETE, TRUNCATE, UPDATE, etc) in an index to other nodes in the cluster. Currently percolate and rt indexes are supported. Only Linux packages and builds support replication, Windows and MacOS packages do not support replication.

Manticore's replication is based on Galera library and features the following:

  • true multi-master - read and write to any node at any time
  • synchronous replication - no slave lag, no data is lost after a node crash
  • hot standby - no downtime during failover (since there is no failover)
  • tightly coupled - all the nodes hold the same state. No diverged data between nodes allowed
  • automatic node provisioning - no need to manually back up the database and restore it on a new node
  • easy to use and deploy
  • detection and automatic eviction of unreliable nodes
  • certification based replication

To use replication in Manticore Search:

  • data_dir option should be set in section "searchd" of the configuration file. Replication is not supported in the plain mode
  • there should be either:
    • a listen directive specified (without specifying a protocol) containing an IP address accessible by other nodes
    • or node_address with an accessible IP address
  • optionally set unique values for server_id on each cluster node. If no value set, the node will try to use the MAC address (or a random number if that fails) to generate the server_id.

If there is no replication listen directive set Manticore will use first couple of free ports in a range of 200 ports after the port at which the daemon is listening (default protocol) for each cluster created. For manual declaration of replication ports the listen directive port range should be defined and these "address - port range" pairs should be different for all Manticore instances on the same host. As a rule of thumb, the port range should specify no less than two ports per cluster.

Replication cluster

Replication cluster is a set of nodes among which a write transaction gets replicated. Replication is configured on the per-index basis. One index can be assigned to only one cluster. There is no restriction on how many indexes a cluster may have. All transactions such as INSERT, REPLACE, DELETE, TRUNCATE in any percolate index belonging to a cluster are replicated to all the other nodes in the cluster. Replication is multi-master, so writes to any particular node or to multiple nodes simultaneously work equally well.

Replication cluster configuration options are:

name

Specifies a name for the cluster. Should be unique.

path

Data directory for a write-set cache replication and incoming indexes from other nodes. Should be unique among the other clusters in the node. Default is data_dir.

nodes

A list of address:port pairs for all the nodes in the cluster (comma separated). A node's API interface should be used for this option. It can contain the current node's address too. This list is used to join a node to the cluster and rejoin it after restart.

options

Options passed directly to Galera replication plugin as described here Galera Documentation Parameters

Write statements

For SQL interface all write statements such as INSERT, REPLACE, DELETE, TRUNCATE, UPDATE that change the content of a cluster's index should use cluster_name:index_name expression in place of an index name to make sure the change is propagated to all replicas in the cluster. An error will be triggered otherwise.

All write statements for HTTP interface to a cluster's index should set cluster property along with index name. An error will be triggered otherwise.

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INSERT INTO posts:weekly_index VALUES ( 'iphone case' )
TRUNCATE RTINDEX click_query:weekly_index
UPDATE INTO posts:rt_tags SET tags=(101, 302, 304) WHERE MATCH ('use') AND id IN (1,101,201)
DELETE FROM clicks:rt WHERE MATCH ('dumy') AND gid>206

Read statements such as CALL PQ, SELECT or DESCRIBE can use either regular index names not prepended with a cluster name or cluster_name:index_name. cluster_name:index_name syntax ignores the cluster name and may be used on an index that doesn't belong to the cluster.

HTTP endpoint json/search could use either a cluster property or not.

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SELECT * FROM weekly_index
CALL PQ('posts:weekly_index', 'document is here')

ID auto generation uses UUID_SHORT similar to MySQL function. It is valid cluster wide UUID when server_id properly configured.

Note: UpdateAttributes statement from API interface to specific index always set proper cluster at server and there is no way to know is update to index got propagated into cluster properly or node diverged and statement updated only local index.

Cluster parameters

Replication plugin options can be changed using SET statement (see the example).

See Galera Documentation Parameters for a list of available options.

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SET CLUSTER click_query GLOBAL 'pc.bootstrap' = 1

Cluster with diverged nodes

Sometimes replicated nodes can diverge from each other. The state of all the nodes might turn into non-primary due to a network split between nodes, a cluster crash, or if the replication plugin hits an exception when determining the primary component. Then it's necessary to select a node and promote it to the primary component.

To determine which node needs to be a reference, compare the last_committed cluster status variable value on all nodes. If all the servers are already running there's no need to start the cluster again. You just need to promote the most advanced node to the primary component with SET statement (see the example).

All other nodes will reconnect to the node and resync their data based on this node.

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SET CLUSTER posts GLOBAL 'pc.bootstrap' = 1

Replication and cluster

To use replication define one listen port for SphinxAPI protocol and one listen for replication address and port range in the config. Define data_dir folder for incoming indexes.

ini
📋
searchd {
  listen   = 9312
  listen   = 192.168.1.101:9360-9370:replication
  data_dir = /var/lib/manticore/
  ...
 }

Create a cluster at the server that has local indexes that need to be replicated

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CREATE CLUSTER posts

Add these local indexes to cluster

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ALTER CLUSTER posts ADD pq_title
ALTER CLUSTER posts ADD pq_clicks

All other nodes that want replica of cluster's indexes should join cluster as

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JOIN CLUSTER posts AT '192.168.1.101:9312'

When running queries for SQL prepend the index name with the cluster name posts: or use cluster property for HTTP request object.

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INSERT INTO posts:pq_title VALUES ( 3, 'test me' )

Now all such queries that modify indexes in the cluster are replicated to all nodes in the cluster.

Creating a replication cluster

To create a replication cluster you should set at least its name.

In case of a single cluster or if the cluster you are creating is the first one path option may be omitted, in this case data_dir option will be used as the cluster path. For all subsequent clusters you need to specify path and this path should be available. nodes option may be also set to enumerate all the nodes in the cluster.

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CREATE CLUSTER posts
CREATE CLUSTER click_query '/var/data/click_query/' as path
CREATE CLUSTER click_query '/var/data/click_query/' as path, 'clicks_mirror1:9312,clicks_mirror2:9312,clicks_mirror3:9312' as nodes

If a cluster is created without the nodes option, the first node that gets joined to the cluster will be saved as nodes.

Joining a replication cluster

To join an existing cluster name and any working node should be set. In case of a single cluster path might be omitted, data_dir will be used as the cluster path. For all subsequent clusters path needs to be set and it should be available.

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JOIN CLUSTER posts AT '10.12.1.35:9312'

A node joins a cluster by getting the data from the node provided and, if successful, it updates node lists in all the other cluster nodes similar to ALTER CLUSTER ... UPDATE nodes. This list is used to rejoin nodes to the cluster on restart.

There are two lists of nodes. One is used to rejoin nodes to the cluster on restart, it is updated across all nodes same way as ALTER CLUSTER ... UPDATE nodes does. Join cluster does the same update automatically. Cluster status shows this list as cluster_post_nodes_set. The second list is a list of all active nodes used for replication. This list doesn't require manual management. ALTER CLUSTER ... UPDATE nodes actually copies this list of nodes to the list of nodes used to rejoin on restart. Cluster status shows this list as cluster_post_nodes_view.

When nodes are located at different network segments or in different datacenters nodes option may be set explicitly. That allows to minimize traffic between nodes and to use gateway nodes for datacenters intercommunication. The following command joins an existing cluster using the nodes option.

Note: that when this syntax is used, cluster_post_nodes_set list is not updated automatically. Use ALTER CLUSTER ... UPDATE nodes to update it.

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JOIN CLUSTER click_query 'clicks_mirror1:9312;clicks_mirror2:9312;clicks_mirror3:9312' as nodes

JOIN CLUSTER completes when a node receives all the necessary data to be in sync with all the other nodes in the cluster.