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LBFactoryMulti.php
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LBFactoryMulti.php
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<?php
/**
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
* http://www.gnu.org/copyleft/gpl.html
*
* @file
*/
namespace Wikimedia\Rdbms;
use InvalidArgumentException;
use LogicException;
use UnexpectedValueException;
/**
* LoadBalancer manager for sites with several "main" database clusters
*
* Each database cluster consists of a "primary" server and any number of replica servers,
* all of which converge, as soon as possible, to contain the same schemas and records. If
* a replication topology has multiple primaries, then the "primary" is merely the preferred
* co-primary for the current context (e.g. datacenter).
*
* For single-primary topologies, the schemas and records of the primary define the "dataset".
* For multiple-primary topologies, the "dataset" is the convergent result of applying/merging
* all committed events (regardless of the co-primary they originated on); it possible that no
* co-primary has yet converged upon this state at any given time (especially when there are
* frequent writes and co-primaries are geographically distant).
*
* A "main" cluster contain a "main" dataset, which consists of data that is compact, highly
* relational (e.g. read by JOIN queries), and essential to one or more sites. The "external"
* clusters each store an "external" dataset, which consists of data that is non-relational
* (e.g. key/value pairs), self-contained (e.g. JOIN queries and transactions thereof never
* involve a main dataset), or too bulky to reside in a main dataset (e.g. text blobs).
*
* The class allows for large site farms to split up their data in the following ways:
* - Vertically shard compact site-specific data by site (e.g. page/comment metadata)
* - Vertically shard compact global data by module (e.g. account/notification data)
* - Horizontally shard any bulk data by blob key (e.g. page/comment content blobs)
*
* @ingroup Database
*/
class LBFactoryMulti extends LBFactory {
/** @var array<string,LoadBalancer> Map of (main section => tracked LoadBalancer) */
private $mainLBs = [];
/** @var array<string,LoadBalancer> Map of (external cluster => tracked LoadBalancer) */
private $externalLBs = [];
/** @var string[] Map of (server name => IP address) */
private $hostsByServerName;
/** @var string[] Map of (database name => main section) */
private $sectionsByDB;
/** @var int[][][] Map of (main section => group => server name => load ratio) */
private $groupLoadsBySection;
/** @var int[][] Map of (external cluster => server name => load ratio) */
private $externalLoadsByCluster;
/** @var array Server config map ("host", "serverName", "load", and "groupLoads" ignored) */
private $serverTemplate;
/** @var array Server config map overriding "serverTemplate" for all external servers */
private $externalTemplateOverrides;
/** @var array[] Map of (main section => server config map overrides) */
private $templateOverridesBySection;
/** @var array[] Map of (external cluster => server config map overrides) */
private $templateOverridesByCluster;
/** @var array Server config override map for all main/external primary DB servers */
private $masterTemplateOverrides;
/** @var array[] Map of (server name => server config map overrides) for all servers */
private $templateOverridesByServer;
/** @var string[]|bool[] A map of (main section => read-only message) */
private $readOnlyBySection;
/** @var array Configuration for the LoadMonitor to use within LoadBalancer instances */
private $loadMonitorConfig;
/** @var DatabaseDomain[] Map of (domain ID => domain instance) */
private $nonLocalDomainCache = [];
/**
* Template override precedence (highest => lowest):
* - templateOverridesByServer
* - masterTemplateOverrides
* - templateOverridesBySection/templateOverridesByCluster
* - externalTemplateOverrides
* - serverTemplate
* Overrides only work on top level keys (so nested values will not be merged).
*
* Server config maps should be of the format Database::factory() requires.
* Additionally, a 'max lag' key should also be set on server maps, indicating how stale the
* data can be before the load balancer tries to avoid using it. The map can have 'is static'
* set to disable blocking replication sync checks (intended for archive servers with
* unchanging data).
*
* @see LBFactory::__construct()
* @param array $conf Additional parameters include:
* - hostsByName: map of (server name => IP address). [optional]
* - sectionsByDB: map of (database => main section). The database name "DEFAULT" is
* interpreted as a catch-all for all databases not otherwise mentioned. If no section
* name is specified for "DEFAULT", then the catch-all section is assumed to be named
* "DEFAULT". [optional]
* - sectionLoads: map of (main section => server name => load ratio); the first host
* listed in each section is the primary DB server for that section. [optional]
* - groupLoadsBySection: map of (main section => group => server name => group load ratio).
* Any ILoadBalancer::GROUP_GENERIC group will be ignored. [optional]
* - externalLoads: map of (cluster => server name => load ratio) map. [optional]
* - serverTemplate: server config map for Database::factory().
* Note that "host", "serverName" and "load" entries will be overridden by
* "groupLoadsBySection" and "hostsByName". [optional]
* - externalTemplateOverrides: server config map overrides for external stores;
* respects the override precedence described above. [optional]
* - templateOverridesBySection: map of (main section => server config map overrides);
* respects the override precedence described above. [optional]
* - templateOverridesByCluster: map of (external cluster => server config map overrides);
* respects the override precedence described above. [optional]
* - masterTemplateOverrides: server config map overrides for masters;
* respects the override precedence described above. [optional]
* - templateOverridesByServer: map of (server name => server config map overrides);
* respects the override precedence described above and applies to both core
* and external storage. [optional]
* - loadMonitor: LoadMonitor::__construct() parameters with "class" field. [optional]
* - readOnlyBySection: map of (main section => message text or false).
* String values make sections read only, whereas anything else does not
* restrict read/write mode. [optional]
* - configCallback: A callback that returns a conf array that can be passed to
* the reconfigure() method. This will be used to autoReconfigure() to load
* any updated configuration.
*/
public function __construct( array $conf ) {
parent::__construct( $conf );
$this->hostsByServerName = $conf['hostsByName'] ?? [];
$this->sectionsByDB = $conf['sectionsByDB'];
$this->sectionsByDB += [ self::CLUSTER_MAIN_DEFAULT => self::CLUSTER_MAIN_DEFAULT ];
$this->groupLoadsBySection = $conf['groupLoadsBySection'] ?? [];
foreach ( ( $conf['sectionLoads'] ?? [] ) as $section => $loadsByServerName ) {
$this->groupLoadsBySection[$section][ILoadBalancer::GROUP_GENERIC] = $loadsByServerName;
}
$this->externalLoadsByCluster = $conf['externalLoads'] ?? [];
$this->serverTemplate = $conf['serverTemplate'] ?? [];
$this->externalTemplateOverrides = $conf['externalTemplateOverrides'] ?? [];
$this->templateOverridesBySection = $conf['templateOverridesBySection'] ?? [];
$this->templateOverridesByCluster = $conf['templateOverridesByCluster'] ?? [];
$this->masterTemplateOverrides = $conf['masterTemplateOverrides'] ?? [];
$this->templateOverridesByServer = $conf['templateOverridesByServer'] ?? [];
$this->readOnlyBySection = $conf['readOnlyBySection'] ?? [];
if ( isset( $conf['loadMonitor'] ) ) {
$this->loadMonitorConfig = $conf['loadMonitor'];
} elseif ( isset( $conf['loadMonitorClass'] ) ) { // b/c
$this->loadMonitorConfig = [ 'class' => $conf['loadMonitorClass'] ];
} else {
$this->loadMonitorConfig = [ 'class' => LoadMonitor::class ];
}
foreach ( $this->externalLoadsByCluster as $cluster => $_ ) {
if ( isset( $this->groupLoadsBySection[$cluster] ) ) {
throw new LogicException(
"External cluster '$cluster' has the same name as a main section/cluster"
);
}
}
}
public function newMainLB( $domain = false ): ILoadBalancerForOwner {
$domainInstance = $this->resolveDomainInstance( $domain );
$database = $domainInstance->getDatabase();
$section = $this->getSectionFromDatabase( $database );
if ( !isset( $this->groupLoadsBySection[$section][ILoadBalancer::GROUP_GENERIC] ) ) {
throw new UnexpectedValueException( "Section '$section' has no hosts defined." );
}
return $this->newLoadBalancer(
$section,
array_merge(
$this->serverTemplate,
$this->templateOverridesBySection[$section] ?? []
),
$this->groupLoadsBySection[$section],
// Use the LB-specific read-only reason if everything isn't already read-only
is_string( $this->readOnlyReason )
? $this->readOnlyReason
: ( $this->readOnlyBySection[$section] ?? false )
);
}
/**
* @param DatabaseDomain|string|false $domain
* @return DatabaseDomain
*/
private function resolveDomainInstance( $domain ) {
if ( $domain instanceof DatabaseDomain ) {
return $domain; // already a domain instance
} elseif ( $domain === false || $domain === $this->localDomain->getId() ) {
return $this->localDomain;
} elseif ( isset( $this->domainAliases[$domain] ) ) {
// This array acts as both the original map and as instance cache.
// Instances pass-through DatabaseDomain::newFromId as-is.
$this->domainAliases[$domain] =
DatabaseDomain::newFromId( $this->domainAliases[$domain] );
return $this->domainAliases[$domain];
}
$cachedDomain = $this->nonLocalDomainCache[$domain] ?? null;
if ( $cachedDomain === null ) {
$cachedDomain = DatabaseDomain::newFromId( $domain );
$this->nonLocalDomainCache = [ $domain => $cachedDomain ];
}
return $cachedDomain;
}
public function getMainLB( $domain = false ): ILoadBalancer {
$domainInstance = $this->resolveDomainInstance( $domain );
$section = $this->getSectionFromDatabase( $domainInstance->getDatabase() );
if ( !isset( $this->mainLBs[$section] ) ) {
$this->mainLBs[$section] = $this->newMainLB( $domain );
}
return $this->mainLBs[$section];
}
public function newExternalLB( $cluster ): ILoadBalancerForOwner {
if ( !isset( $this->externalLoadsByCluster[$cluster] ) ) {
throw new InvalidArgumentException( "Unknown cluster '$cluster'" );
}
return $this->newLoadBalancer(
$cluster,
array_merge(
$this->serverTemplate,
$this->externalTemplateOverrides,
$this->templateOverridesByCluster[$cluster] ?? []
),
[ ILoadBalancer::GROUP_GENERIC => $this->externalLoadsByCluster[$cluster] ],
$this->readOnlyReason
);
}
public function getExternalLB( $cluster ): ILoadBalancer {
if ( !isset( $this->externalLBs[$cluster] ) ) {
$this->externalLBs[$cluster] = $this->newExternalLB(
$cluster
);
}
return $this->externalLBs[$cluster];
}
public function getAllMainLBs(): array {
$lbs = [];
foreach ( $this->sectionsByDB as $db => $section ) {
if ( !isset( $lbs[$section] ) ) {
$lbs[$section] = $this->getMainLB( $db );
}
}
return $lbs;
}
public function getAllExternalLBs(): array {
$lbs = [];
foreach ( $this->externalLoadsByCluster as $cluster => $unused ) {
$lbs[$cluster] = $this->getExternalLB( $cluster );
}
return $lbs;
}
protected function getLBsForOwner() {
foreach ( $this->mainLBs as $lb ) {
yield $lb;
}
foreach ( $this->externalLBs as $lb ) {
yield $lb;
}
}
/**
* Make a new load balancer object based on template and load array
*
* @param string $clusterName
* @param array $serverTemplate
* @param array $groupLoads
* @param string|false $readOnlyReason
* @return LoadBalancer
*/
private function newLoadBalancer(
string $clusterName,
array $serverTemplate,
array $groupLoads,
$readOnlyReason
) {
$lb = new LoadBalancer( array_merge(
$this->baseLoadBalancerParams(),
[
'servers' => $this->makeServerConfigArrays( $serverTemplate, $groupLoads ),
'loadMonitor' => $this->loadMonitorConfig,
'readOnlyReason' => $readOnlyReason,
'clusterName' => $clusterName
]
) );
$this->initLoadBalancer( $lb );
return $lb;
}
/**
* Make a server array as expected by LoadBalancer::__construct()
*
* @param array $serverTemplate Server config map
* @param int[][] $groupLoads Map of (group => server name => load)
* @return array[] List of server config maps
*/
private function makeServerConfigArrays( array $serverTemplate, array $groupLoads ) {
// The primary DB server is the first host explicitly listed in the generic load group
if ( !$groupLoads[ILoadBalancer::GROUP_GENERIC] ) {
throw new UnexpectedValueException( "Empty generic load array; no primary DB defined." );
}
$groupLoadsByServerName = [];
foreach ( $groupLoads as $group => $loadByServerName ) {
foreach ( $loadByServerName as $serverName => $load ) {
$groupLoadsByServerName[$serverName][$group] = $load;
}
}
// Get the ordered map of (server name => load); the primary DB server is first
$genericLoads = $groupLoads[ILoadBalancer::GROUP_GENERIC];
// Implicitly append any hosts that only appear in custom load groups
$genericLoads += array_fill_keys( array_keys( $groupLoadsByServerName ), 0 );
$servers = [];
foreach ( $genericLoads as $serverName => $load ) {
$servers[] = array_merge(
$serverTemplate,
$servers ? [] : $this->masterTemplateOverrides,
$this->templateOverridesByServer[$serverName] ?? [],
[
'host' => $this->hostsByServerName[$serverName] ?? $serverName,
'serverName' => $serverName,
'load' => $load,
'groupLoads' => $groupLoadsByServerName[$serverName] ?? []
]
);
}
return $servers;
}
/**
* @param string $database
* @return string Main section name
*/
private function getSectionFromDatabase( $database ) {
return $this->sectionsByDB[$database]
?? $this->sectionsByDB[self::CLUSTER_MAIN_DEFAULT]
?? self::CLUSTER_MAIN_DEFAULT;
}
public function reconfigure( array $conf ): void {
if ( !$conf ) {
return;
}
foreach ( $this->mainLBs as $lb ) {
// Approximate what LBFactoryMulti::__construct does (T346365)
$groupLoads = $conf['groupLoadsBySection'][$lb->getClusterName()] ?? [];
$groupLoads[ILoadBalancer::GROUP_GENERIC] = $conf['sectionLoads'][$lb->getClusterName()];
$config = [
'servers' => $this->makeServerConfigArrays( $conf['serverTemplate'] ?? [], $groupLoads )
];
$lb->reconfigure( $config );
}
foreach ( $this->externalLBs as $lb ) {
$groupLoads = [
ILoadBalancer::GROUP_GENERIC => $conf['externalLoads'][$lb->getClusterName()]
];
$config = [
'servers' => $this->makeServerConfigArrays( $conf['serverTemplate'] ?? [], $groupLoads )
];
$lb->reconfigure( $config );
}
}
}

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