501 lines
22 KiB
PHP
501 lines
22 KiB
PHP
<?php
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/**
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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* http://www.gnu.org/copyleft/gpl.html
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*
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* @file
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*/
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namespace Wikimedia\Rdbms;
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/**
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* This class is a delegate to ILBFactory for a given database cluster
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*
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* ILoadBalancer tracks the database connections and transactions for a given database cluster.
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* A "cluster" is considered to be the set of database servers that manage a given dataset.
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* Within a given cluster, each database server can have one of the following roles:
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* - sole-primary: the server used by this datacenter for writes from the application
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* - co-primary: one of several servers used by this datacenter for writes from the application,
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* relying on asynchronous replication to synchronize their copies of the dataset
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* - replica: a server used only for reads from the application, relying on asynchronous
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* replication to apply writes from the primary server or co-primary servers
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* - static clone: a server that only accepts reads from the application, does not replicate,
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* and has a copy of the final dataset, which must be static (all the servers reject writes)
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*
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* Single-datacenter database clusters consist of either:
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* - A sole-primary server and zero or more replica servers
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* - A set of static clone servers
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*
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* Multi-datacenter database clusters either consist of either:
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* - A sole-primary server and zero or more replica servers in the "primary datacenter"
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* (the one datacenter meant to handle requests/jobs that mutate the database), and zero or
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* more replica servers in each "secondary datacenter" (all the other datacenters)
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* - A co-primary server and zero or more replica servers within each datacenter
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* - A set of static clone servers in each datacenter
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*
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* The term "primary" refers to the server used by this datacenter for handling writes,
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* whether it is a sole-primary or co-primary.
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*
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* The "servers" configuration array contains the list of database servers to use for operations
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* originating from the the local datacenter. The first entry must refer to the server to use for
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* write and read-for-write operations (e.g. the "writer server"):
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* - If there is a primary server, then the first entry must refer to it, even if the primary
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* server resides in a remote datacenter
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* - If there are co-primary servers, then the first entry must refer to the one in the local
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* datacenter
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* - If the servers are static clones, then the first entry can refer to any of them, since the
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* concept of a "writer server" is merely nominal
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*
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* On an infrastructure level, circular replication setups can have more than one database server
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* act as a replication "source" within the same datacenter, provided that no more than one of the
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* servers are writable at any time, namely the "writer server". The other source servers will be
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* treated as replicas by the load balancer, but can be quickly promoted to the "writer server" by
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* the site admin as needed.
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*
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* Likewise, Galera Cluster setups still require the choice of a single "writer server" for each
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* datacenter. Limiting the number of servers that initiate transactions helps reduce the rate of
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* aborted transactions due to wsrep conflicts.
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*
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* By default, each DB server uses DBO_DEFAULT for its 'flags' setting, unless explicitly set
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* otherwise in configuration. DBO_DEFAULT behavior depends on whether 'cliMode' is set:
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* - In CLI mode, the flag has no effect with regards to LoadBalancer.
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* - In non-CLI mode, the flag causes implicit transactions to be used; the first query on
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* a database starts a transaction on that database. The transactions are meant to remain
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* pending until either commitPrimaryChanges() or rollbackPrimaryChanges() is called. The
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* application must have some point where it calls commitPrimaryChanges() near the end of
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* the PHP request.
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* Every iteration of beginPrimaryChanges()/commitPrimaryChanges() is called a "transaction round".
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* Rounds are useful on the primary DB connections because they make single-DB (and by and large
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* multi-DB) updates in web requests all-or-nothing. Also, transactions on replica DBs are useful
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* when REPEATABLE-READ or SERIALIZABLE isolation is used because all foreign keys and constraints
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* hold across separate queries in the DB transaction since the data appears within a consistent
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* point-in-time snapshot.
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*
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* The typical caller will use LoadBalancer::getConnection( DB_* ) to yield a database
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* connection handle. The choice of which DB server to use is based on pre-defined loads for
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* weighted random selection, adjustments thereof by LoadMonitor, and the amount of replication
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* lag on each DB server. Lag checks might cause problems in certain setups, so they should be
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* tuned in the server configuration maps as follows:
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* - Sole-primary + N Replica(s): set 'max lag' to an appropriate threshold for avoiding any
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* replica database lagged by this much or more. If all replicas are this lagged, then the
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* load balancer considers the cluster to be read-only.
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* - Per-datacenter co-primary + N Replica(s): set 'max lag' to an appropriate threshold for
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* avoiding any replica database lagged by this much or more. If all replicas are this
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* lagged, then the load balancer considers the cluster to be read-only.
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* - Read-only archive clones: set 'is static' in the server configuration maps. This will
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* treat all such DBs as having 0 lag.
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* - Externally updated dataset clones: set 'is static' in the server configuration maps.
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* This will treat all such DBs as having 0 lag.
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* - SQL load balancing proxy: any proxy should handle lag checks on its own, so the 'max lag'
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* parameter should probably be set to INF in the server configuration maps. This will make
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* the load balancer ignore whatever it detects as the lag of the logical replica is (which
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* would probably just randomly bounce around).
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*
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* If using a SQL proxy service, it would probably be best to have two proxy hosts for the load
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* balancer to talk to. One would be the 'host' of the "writer server" entry and another for the
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* (logical) replica server entry. The proxy could map the load balancer's "replica" DB to any
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* number of physical replica DBs.
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*
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* @since 1.28
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* @ingroup Database
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*/
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interface ILoadBalancer {
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/**
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* Request a replica DB connection. Can't be used as a binary flag with bitwise operators!
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*/
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public const DB_REPLICA = -1;
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/**
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* Request a primary, write-enabled DB connection. Can't be used as a binary flag with bitwise
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* operators!
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* @since 1.36
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*/
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public const DB_PRIMARY = -2;
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/** Domain specifier when no specific database needs to be selected */
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public const DOMAIN_ANY = '';
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/** The generic query group */
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public const GROUP_GENERIC = '';
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/** Yield a tracked autocommit-mode handle (reuse existing ones) */
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public const CONN_TRX_AUTOCOMMIT = 1;
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/**
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* Yield an untracked, low-timeout, autocommit-mode handle (to gauge server health)
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* @internal
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*/
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public const CONN_UNTRACKED_GAUGE = 2;
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/**
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* Yield null on connection failure instead of throwing an exception
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* @internal
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*/
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public const CONN_SILENCE_ERRORS = 4;
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/**
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* Get the name of the overall cluster of database servers managing the dataset
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*
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* Note that the cluster might contain servers in multiple datacenters.
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* The load balancer instance only needs to be aware of the local replica servers,
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* along with either the sole-primary server or the local co-primary server.
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*
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* This is useful for identifying a cluster or replicated dataset, even when:
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* - The primary server is sometimes swapped with another one
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* - The cluster/dataset is replicated among multiple datacenters, with one "primary"
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* datacenter having the writable primary server and the other datacenters having a
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* read-only replica in the "primary" server slot
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* - The dataset is replicated among multiple datacenters, via circular replication,
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* with each datacenter having its own "co-primary" server
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*
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* @return string
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* @since 1.36
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*/
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public function getClusterName(): string;
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/**
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* Get the local (and default) database domain ID of connection handles
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*
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* @see DatabaseDomain
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* @return string Database domain ID; this specifies DB name, schema, and table prefix
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* @since 1.31
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*/
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public function getLocalDomainID(): string;
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/**
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* @param DatabaseDomain|string|false $domain Database domain
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* @return string Value of $domain if it is foreign or the local domain otherwise
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* @since 1.32
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*/
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public function resolveDomainID( $domain ): string;
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/**
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* Indicate whether the tables on this domain are only temporary tables for testing
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*
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* In "temporary tables mode", the CONN_TRX_AUTOCOMMIT flag is ignored
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*
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* @param bool $value
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* @param string $domain
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* @return bool Whether "temporary tables mode" was active
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* @since 1.34
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*/
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public function setTempTablesOnlyMode( $value, $domain );
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/**
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* Get the specific server index of the reader connection for a given group
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*
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* This takes into account load ratios and lag times. It should return a consistent
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* index during the life time of the load balancer. This initially checks replica DBs
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* for connectivity to avoid returning an unusable server. This means that connections
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* might be attempted by calling this method (usually one at the most but possibly more).
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* Subsequent calls with the same $group will not need to make new connection attempts
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* since the acquired connection for each group is preserved.
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*
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* @param string|false $group Query group or false for the generic group
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* @return int|false Specific server index, or false if no DB handle can be obtained
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*/
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public function getReaderIndex( $group = false );
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/**
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* Get a lazy-connecting database handle for a specific or virtual (DB_PRIMARY/DB_REPLICA) server index
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*
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* The server index, $i, can be one of the following:
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* - DB_REPLICA: a server index will be selected by the load balancer based on read
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* weight, connectivity, and replication lag. Note that the primary server might be
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* configured with read weight. If $groups is empty then it means "the generic group",
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* in which case all servers defined with read weight will be considered. Additional
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* query groups can be configured, having their own list of server indexes and read
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* weights. If a query group list is provided in $groups, then each recognized group
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* will be tried, left-to-right, until server index selection succeeds or all groups
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* have been tried, in which case the generic group will be tried.
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* - DB_PRIMARY: the primary server index will be used; the same as ServerInfo::WRITER_INDEX.
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* The value of $groups should be [] when using this server index.
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* - Specific server index: a positive integer can be provided to use the server with
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* that index. An error will be thrown in no such server index is recognized. This
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* server selection method is usually only useful for internal load balancing logic.
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* The value of $groups should be [] when using a specific server index.
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*
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* Handle sharing is very useful when callers get DB_PRIMARY handles that are transaction
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* round aware (the default). All such callers will operate within a single transaction as
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* a consequence. The same applies to DB_REPLICA that are samely query grouped (the default)
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* and transaction round aware (the default).
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*
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* Use CONN_TRX_AUTOCOMMIT to use a separate pool of only autocommit handles. This flag is
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* ignored for databases with ATTR_DB_LEVEL_LOCKING (e.g. sqlite) in order to avoid deadlocks.
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* getServerAttributes() can be used to check this attribute beforehand. Avoid using begin()
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* and commit() on such handles. If handle methods like startAtomic() and endAtomic() must be
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* used on the handles, callers should at least make sure that the atomic sections are closed
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* on failure via try/catch and cancelAtomic().
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*
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* Use CONN_UNTRACKED_GAUGE to get a new, untracked, handle, that uses a low connection timeout, a low
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* read timeout, and autocommit mode. This flag is intended for use only be internal callers.
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*
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* CONN_UNTRACKED_GAUGE and CONN_TRX_AUTOCOMMIT are incompatible.
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*
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* @see ILoadBalancer::getServerAttributes()
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*
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* @param int $i Specific (overrides $groups) or virtual (DB_PRIMARY/DB_REPLICA) server index
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* @param string[]|string $groups Query group(s) in preference order; [] for the default group
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* @param string|false $domain DB domain ID or false for the local domain
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* @param int $flags Bitfield of CONN_* class constants
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* @return IDatabase|false This returns false on failure if CONN_SILENCE_ERRORS is set
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*/
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public function getConnection( $i, $groups = [], $domain = false, $flags = 0 );
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/**
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* Get a DB handle for a specific server index
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*
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* This is an internal utility method for methods like LoadBalancer::getConnectionInternal()
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* and DBConnRef to create the underlying connection to a concrete server.
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*
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* The following is the responsibility of the caller:
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*
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* - translate any virtual server indexes (DB_PRIMARY/DB_REPLICA) to a real server index.
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* - enforce read-only mode on primary DB handle if there is high replication lag.
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*
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* @see ILoadBalancer::getConnection()
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*
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* @internal Only for use within ILoadBalancer/ILoadMonitor
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* @param int $i Specific server index
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* @param string $domain Resolved DB domain
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* @param int $flags Bitfield of class CONN_* constants
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* @return IDatabaseForOwner|false This returns false on failure if CONN_SILENCE_ERRORS is set
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* @throws DBError If no DB handle could be obtained and CONN_SILENCE_ERRORS is not set
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*/
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public function getServerConnection( $i, $domain, $flags = 0 );
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/**
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* @deprecated since 1.39, use ILoadBalancer::getConnection() instead.
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* @param int $i Specific or virtual (DB_PRIMARY/DB_REPLICA) server index
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* @param string[]|string $groups Query group(s) in preference order; [] for the default group
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* @param string|false $domain DB domain ID or false for the local domain
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* @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT)
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* @return DBConnRef
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*/
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public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ): DBConnRef;
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/**
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* @internal Only to be used by DBConnRef
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* @param int $i Specific (overrides $groups) or virtual (DB_PRIMARY/DB_REPLICA) server index
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* @param string[]|string $groups Query group(s) in preference order; [] for the default group
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* @param string|false $domain DB domain ID or false for the local domain
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* @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT)
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* @return IDatabase
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*/
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public function getConnectionInternal( $i, $groups = [], $domain = false, $flags = 0 ): IDatabase;
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/**
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* Get a DB handle, suitable for migrations and schema changes, for a server index
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*
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* The DBConnRef methods simply proxy an underlying IDatabase object which
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* takes care of the actual connection and query logic.
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*
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* The CONN_TRX_AUTOCOMMIT flag is ignored for databases with ATTR_DB_LEVEL_LOCKING
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* (e.g. sqlite) in order to avoid deadlocks. getServerAttributes()
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* can be used to check such flags beforehand. Avoid the use of begin() or startAtomic()
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* on any CONN_TRX_AUTOCOMMIT connections.
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*
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* @see ILoadBalancer::getConnection() for parameter information
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* @param int $i Specific or virtual (DB_PRIMARY/DB_REPLICA) server index
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* @param string[]|string $groups Query group(s) in preference order; [] for the default group
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* @param string|false $domain DB domain ID or false for the local domain
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* @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT)
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* @return DBConnRef
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*/
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public function getMaintenanceConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ): DBConnRef;
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/**
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* Get the number of servers defined in configuration
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*
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* @return int
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*/
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public function getServerCount();
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/**
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* Whether there are any replica servers configured
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*
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* This scans the list of servers defined in configuration, checking for:
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* - Servers that are listed after the primary and not flagged with "is static";
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* such servers are assumed to be typical streaming replicas
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* - Servers that are listed after the primary and flagged with "is static";
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* such servers are assumed to have a clone of the static dataset (matching the primary)
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*
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* @return bool
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* @since 1.34
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*/
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public function hasReplicaServers();
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/**
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* Whether any replica servers use streaming replication from the primary server
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*
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* This scans the list of servers defined in configuration, checking for:
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* - Servers that are listed after the primary and not flagged with "is static";
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* such servers are assumed to be typical streaming replicas
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*
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* It is possible for some replicas to be configured with "is static" but not
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* others, though it generally should either be set for all or none of the replicas.
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*
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* If this returns false, this means that there is generally no reason to execute
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* replication wait logic for session consistency and lag reduction.
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*
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* @return bool
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* @since 1.34
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*/
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public function hasStreamingReplicaServers();
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/**
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* Get the readable name of the server with the specified index
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*
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* @param int $i Specific server index
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* @return string Readable server name, falling back to the hostname or IP address
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*/
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public function getServerName( $i ): string;
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/**
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* Return the server configuration map for the server with the specified index
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*
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* @param int $i Specific server index
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* @return array|false Server configuration map; false if the index is invalid
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* @since 1.31
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*/
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public function getServerInfo( $i );
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/**
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* Get the RDBMS type of the server with the specified index (e.g. "mysql", "sqlite")
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*
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* @param int $i Specific server index
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* @return string One of (mysql,postgres,sqlite,...) or "unknown" for bad indexes
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* @since 1.30
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*/
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public function getServerType( $i );
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/**
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* Get basic attributes of the server with the specified index without connecting
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*
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* @param int $i Specific server index
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* @return array (Database::ATTRIBUTE_* constant => value) for all such constants
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* @since 1.31
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*/
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public function getServerAttributes( $i );
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/**
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* Get the current primary replication position
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*
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* @return DBPrimaryPos|false Returns false if not applicable
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* @throws DBError
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* @since 1.37
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*/
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public function getPrimaryPos();
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/**
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* Whether there are pending changes or callbacks in a transaction by this thread
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* @return bool
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* @since 1.37
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*/
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public function hasPrimaryChanges();
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/**
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* Determine whether an explicit transaction is active on any open primary
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* connection.
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* @return bool
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* @since 1.39
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*/
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public function explicitTrxActive();
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/**
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* Check if this load balancer object had any recent or still
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* pending writes issued against it by this PHP thread
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*
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* @param float|null $age How many seconds ago is "recent" [defaults to mWaitTimeout]
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* @return bool
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* @since 1.37
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*/
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public function hasOrMadeRecentPrimaryChanges( $age = null );
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/**
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* @note This method may trigger a DB connection if not yet done
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* @return string|false Reason the primary is read-only or false if it is not
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*/
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public function getReadOnlyReason();
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/**
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* @return bool
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*/
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public function pingAll();
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/**
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* Get the name and lag time of the most-lagged replica server
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*
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* This is useful for maintenance scripts that need to throttle their updates.
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* May attempt to open connections to replica DBs on the default DB. If there is
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* no lag, the maximum lag will be reported as -1.
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*
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* @return array{0:string,1:float|int|false,2:int} (host, max lag, index of max lagged host)
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*/
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public function getMaxLag();
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/**
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* Get an estimate of replication lag (in seconds) for each server
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*
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* Results are cached for a short time in memcached/process cache
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*
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* Values may be "false" if replication is too broken to estimate
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*
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* @return float[]|int[]|false[] Map of (server index => lag) in order of server index
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*/
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public function getLagTimes();
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/**
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* Wait for a replica DB to reach a specified primary position
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*
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* If $conn is not a replica server connection, then this will return true.
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* Otherwise, if $pos is not provided, this will connect to the primary server
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* to get an accurate position.
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*
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* @param IDatabase $conn Replica DB
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* @return bool Success
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* @since 1.37
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*/
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public function waitForPrimaryPos( IDatabase $conn );
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/**
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* Set a callback via IDatabase::setTransactionListener() on
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* all current and future primary connections of this load balancer
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*
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* @param string $name Callback name
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* @param callable|null $callback
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*/
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public function setTransactionListener( $name, ?callable $callback = null );
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/**
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* Make certain table names use their own database, schema, and table prefix
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* when passed into SQL queries pre-escaped and without a qualified database name
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*
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* For example, "user" can be converted to "myschema.mydbname.user" for convenience.
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* Appearances like `user`, somedb.user, somedb.someschema.user will used literally.
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*
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* Calling this twice will completely clear any old table aliases. Also, note that
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* callers are responsible for making sure the schemas and databases actually exist.
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*
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* @param array[] $aliases Map of (table => (dbname, schema, prefix) map)
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*/
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public function setTableAliases( array $aliases );
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/**
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* Convert certain database domains to alternative ones.
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*
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* This can be used for backwards compatibility logic.
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*
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* @param DatabaseDomain[]|string[] $aliases Map of (domain alias => domain)
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* @since 1.35
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*/
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public function setDomainAliases( array $aliases );
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}
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