In the event that the Manticore search daemon stops with no remaining nodes in the cluster to serve requests, recovery is necessary. Due to the multi-master nature of the Galera library used for replication, Manticore replication cluster is a single logical entity that maintains the consistency of its nodes and data, and the status of the entire cluster. This allows for safe writes on multiple nodes simultaneously and ensures the integrity of the cluster.

However, this also poses challenges. Let's examine several scenarios, using a cluster of nodes A, B, and C, to see what needs to be done when some or all nodes become unavailable.

When node A is stopped, the other nodes receive a "normal shutdown" message. The cluster size is reduced, and a quorum re-calculation takes place.

Upon starting node A, it joins the cluster and will not serve any write transactions until it is fully synchronized with the cluster. If the writeset cache on donor nodes B or C (which can be controlled with the Galera cluster's gcache.size) still contains all of the transactions missed at node A, node A will receive a fast incremental state transfer (IST), that is, a transfer of only missed transactions. If not, a snapshot state transfer (SST) will occur, which involves the transfer of table files.

In the scenario where nodes A and B are stopped, the cluster size is reduced to one, with node C forming the primary component to handle write transactions.

Nodes A and B can then be started as usual and will join the cluster after start-up. Node C acts as the donor, providing the state transfer to nodes A and B.

All nodes are stopped as usual and the cluster is off.

The problem now is how to initialize the cluster. It's important that on a clean shutdown of searchd the nodes write the number of last executed transaction into the cluster directory grastate.dat file along with flag safe_to_bootstrap. The node which was stopped last will have option safe_to_bootstrap: 1 and the most advanced seqno number.

It is important that this node starts first to form the cluster. To bootstrap a cluster the server should be started on this node with flag --new-cluster. On Linux you can also run manticore_new_cluster which will start Manticore in --new-cluster mode via systemd.

If another node starts first and bootstraps the cluster, then the most advanced node joins that cluster, performs full SST and receives a table file where some transactions are missed in comparison with the table files it got before. That is why it is important to start first the node which was shut down last, it should have flag safe_to_bootstrap: 1 in grastate.dat.

In the event of a crash or network failure causing Node A to disappear from the cluster, nodes B and C will attempt to reconnect with Node A. Upon failure, they will remove Node A from the cluster. With two out of the three nodes still running, the cluster maintains its quorum and continues to operate normally.

When Node A is restarted, it will join the cluster automatically, as outlined in Case 1.

Nodes A and B have gone offline. Node C is unable to form a quorum on its own as 1 node is less than half of the total nodes (3). As a result, the cluster on node C is shifted to a non-primary state and rejects any write transactions with an error message.

Meanwhile, node C waits for the other nodes to connect and also tries to connect to them. If this happens, and the network is restored and nodes A and B are back online, the cluster will automatically reform. If nodes A and B are just temporarily disconnected from node C but can still communicate with each other, they will continue to operate as normal, as they still form the quorum.

SET CLUSTER posts GLOBAL 'pc.bootstrap' = 1

POST /cli -d "
SET CLUSTER posts GLOBAL 'pc.bootstrap' = 1
"

t's important to note that before executing this command, you must confirm that the other nodes are truly unreachable. Otherwise, a split-brain scenario may occur and separate clusters may form.

All nodes have crashed. In this situation, the grastate.dat file in the cluster directory has not been updated and does not contain a valid seqnosequence number.

If this occurs, someone needs to locate the node with the most recent data and start the server on it using the --new-cluster-force command line key. All other nodes will start as normal, as described in Case 3). On Linux, you can also use the manticore_new_cluster --force, command, which will start Manticore in --new-cluster-force mode via systemd.

Split-brain can cause the cluster to transition into a non-primary state. For example, consider a cluster comprised of an even number of nodes (four), such as two pairs of nodes located in different data centers. If a network failure interrupts the connection between the data centers, split-brain occurs as each group of nodes holds exactly half of the quorum. As a result, both groups stop handling write transactions, since the Galera replication model prioritizes data consistency, and the cluster cannot accept write transactions without a quorum. However, nodes in both groups attempt to reconnect with the nodes from the other group in an effort to restore the cluster.

SET CLUSTER posts GLOBAL 'pc.bootstrap' = 1

POST /cli -d "
SET CLUSTER posts GLOBAL 'pc.bootstrap' = 1
"

However, it's important to note that if the statement is issued at both groups, it will result in the formation of two separate clusters, and the subsequent network recovery will not result in the groups rejoining.

Manticore Search implements an SQL interface using the MySQL protocol, allowing any MySQL library or connector and many MySQL clients to be used to connect to Manticore Search and work with it as if it were a MySQL server, not Manticore.

However, the SQL dialect is different and implements only a subset of the SQL commands or functions available in MySQL. Additionally, there are clauses and functions that are specific to Manticore Search, such as the MATCH() clause for full-text search.

Manticore Search does not support server-side prepared statements, but client-side prepared statements can be used. It is important to note that Manticore implements the multi-value (MVA) data type, which has no equivalent in MySQL or libraries implementing prepared statements. In these cases, the MVA values must be crafted in the raw query.

Some MySQL clients/connectors require values for user/password and/or database name. Since Manticore Search does not have the concept of databases and there is no user access control implemented, these values can be set arbitrarily as Manticore will simply ignore them.

The default port for the SQL interface is 9306 and it's enabled by default.

You can configure the MySQL port in the searchd section of the configuration file using the listen directive like this:

searchd {
...
   listen = 127.0.0.1:9306:mysql
...
}

Keep in mind that Manticore doesn't have user authentication, so make sure that the MySQL port is not accessible to anyone outside of your network.

A separate MySQL port can be used for performing "VIP" connections. When connecting to this port, the thread pool is bypassed, and a new dedicated thread is always created. This is useful in cases of severe overload, where the server would either stall or prevent a connection through the regular port.

searchd {
...
   listen = 127.0.0.1:9306:mysql
   listen = 127.0.0.1:9307:mysql_vip
...
}

The easiest way to connect to Manticore is by using a standard MySQL client:

mysql -P9306 -h0

The MySQL protocol supports SSL encryption. Secure connections can be made on the same mysql listening port.

Compression can be used with MySQL connections and is available to clients by default. The client just needs to specify that the connection should use compression.

An example using the MySQL client:

mysql -P9306 -h0 -C

Compression can be used in both secured and non-secured connections.

The official MySQL connectors can be used to connect to Manticore Search, however they might require certain settings passed in the DSN string as the connector can try running certain SQL commands not implemented yet in Manticore.

JDBC Connector 6.x and above require Manticore Search 2.8.2 or greater and the DSN string should contain the following options:

jdbc:mysql://IP:PORT/DB/?characterEncoding=utf8&maxAllowedPacket=512000&serverTimezone=XXX

By default Manticore Search will report it's own version to the connector, however this may cause some troubles. To overcome that mysql_version_string directive in searchd section of the configuration should be set to a version lower than 5.1.1:

searchd {
...
   mysql_version_string = 5.0.37
...
}

.NET MySQL connector uses connection pools by default. To correctly get the statistics of SHOW META, queries along with SHOW META command should be sent as a single multistatement (SELECT ...;SHOW META). If pooling is enabled option Allow Batch=True is required to be added to the connection string to allow multistatements:

Server=127.0.0.1;Port=9306;Database=somevalue;Uid=somevalue;Pwd=;Allow Batch=True;

Manticore can be accessed using ODBC. It's recommended to set charset=UTF8 in the ODBC string. Some ODBC drivers will not like the reported version by the Manticore server as they will see it as a very old MySQL server. This can be overridden with mysql_version_string option.

Manticore SQL over MySQL supports C-style comment syntax. Everything from an opening /* sequence to a closing */ sequence is ignored. Comments can span multiple lines, can not nest, and should not get logged. MySQL specific /*! ... */ comments are also currently ignored. (As the comments support was rather added for better compatibility with mysqldump produced dumps, rather than improving general query interoperability between Manticore and MySQL.)

SELECT /*! SQL_CALC_FOUND_ROWS */ col1 FROM table1 WHERE ...