368 lines
11 KiB
C++
368 lines
11 KiB
C++
/*
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* Copyright (c) 2016 MariaDB Corporation Ab
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*
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* Use of this software is governed by the Business Source License included
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* in the LICENSE.TXT file and at www.mariadb.com/bsl11.
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*
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* Change Date: 2020-01-01
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*
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* On the date above, in accordance with the Business Source License, use
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* of this software will be governed by version 2 or later of the General
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* Public License.
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*/
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#include "readwritesplit.hh"
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#include <stdio.h>
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#include <strings.h>
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#include <string.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <maxscale/router.h>
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using namespace maxscale;
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/**
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* The functions that implement back end selection for the read write
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* split router. All of these functions are internal to that router and
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* not intended to be called from elsewhere.
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*/
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/**
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* Check whether it's possible to use this server as a slave
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*
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* @param server The slave candidate
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* @param master The master server or NULL if no master is available
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*
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* @return True if this server is a valid slave candidate
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*/
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static bool valid_for_slave(const SRWBackend& backend, const SRWBackend& master)
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{
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return (backend->is_slave() || backend->is_relay()) &&
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(!master || backend != master);
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}
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/**
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* @brief Find the best slave candidate
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*
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* This function iterates through @c backend and tries to find the best backend
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* reference that is not in use. @c cmpfun will be called to compare the backends.
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*
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* @param rses Router client session
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* @param master The master server
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* @param cmpfun qsort() compatible comparison function
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*
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* @return The best slave backend reference or NULL if no candidates could be found
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*/
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static SRWBackend get_slave_candidate(const SRWBackendList& backends, const SRWBackend& master,
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int (*cmpfun)(const SRWBackend&, const SRWBackend&))
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{
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SRWBackend candidate;
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for (SRWBackendList::const_iterator it = backends.begin();
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it != backends.end(); it++)
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{
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const SRWBackend& backend = *it;
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if (!backend->in_use() && backend->can_connect() &&
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valid_for_slave(backend, master))
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{
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if (candidate)
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{
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if (cmpfun(candidate, backend) > 0)
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{
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candidate = backend;
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}
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}
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else
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{
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candidate = backend;
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}
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}
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}
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return candidate;
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}
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/** Compare number of connections from this router in backend servers */
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static int backend_cmp_router_conn(const SRWBackend& a, const SRWBackend& b)
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{
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SERVER_REF *first = a->backend();
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SERVER_REF *second = b->backend();
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if (first->weight == 0 && second->weight == 0)
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{
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return first->connections - second->connections;
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}
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else if (first->weight == 0)
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{
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return 1;
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}
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else if (second->weight == 0)
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{
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return -1;
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}
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return ((1000 + 1000 * first->connections) / first->weight) -
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((1000 + 1000 * second->connections) / second->weight);
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}
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/** Compare number of global connections in backend servers */
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static int backend_cmp_global_conn(const SRWBackend& a, const SRWBackend& b)
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{
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SERVER_REF *first = a->backend();
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SERVER_REF *second = b->backend();
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if (first->weight == 0 && second->weight == 0)
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{
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return first->server->stats.n_current -
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second->server->stats.n_current;
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}
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else if (first->weight == 0)
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{
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return 1;
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}
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else if (second->weight == 0)
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{
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return -1;
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}
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return ((1000 + 1000 * first->server->stats.n_current) / first->weight) -
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((1000 + 1000 * second->server->stats.n_current) / second->weight);
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}
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/** Compare replication lag between backend servers */
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static int backend_cmp_behind_master(const SRWBackend& a, const SRWBackend& b)
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{
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SERVER_REF *first = a->backend();
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SERVER_REF *second = b->backend();
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if (first->weight == 0 && second->weight == 0)
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{
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return first->server->rlag -
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second->server->rlag;
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}
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else if (first->weight == 0)
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{
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return 1;
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}
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else if (second->weight == 0)
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{
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return -1;
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}
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return ((1000 + 1000 * first->server->rlag) / first->weight) -
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((1000 + 1000 * second->server->rlag) / second->weight);
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}
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/** Compare number of current operations in backend servers */
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static int backend_cmp_current_load(const SRWBackend& a, const SRWBackend& b)
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{
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SERVER_REF *first = a->backend();
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SERVER_REF *second = b->backend();
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if (first->weight == 0 && second->weight == 0)
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{
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return first->server->stats.n_current_ops - second->server->stats.n_current_ops;
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}
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else if (first->weight == 0)
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{
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return 1;
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}
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else if (second->weight == 0)
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{
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return -1;
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}
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return ((1000 + 1000 * first->server->stats.n_current_ops) / first->weight) -
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((1000 + 1000 * second->server->stats.n_current_ops) / second->weight);
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}
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/**
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* The order of functions _must_ match with the order the select criteria are
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* listed in select_criteria_t definition in readwritesplit.h
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*/
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int (*criteria_cmpfun[LAST_CRITERIA])(const SRWBackend&, const SRWBackend&) =
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{
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NULL,
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backend_cmp_global_conn,
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backend_cmp_router_conn,
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backend_cmp_behind_master,
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backend_cmp_current_load
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};
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/**
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* @brief Log server connections
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*
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* @param criteria Slave selection criteria
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* @param rses Router client session
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*/
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static void log_server_connections(select_criteria_t criteria, const SRWBackendList& backends)
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{
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MXS_INFO("Servers and %s connection counts:",
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criteria == LEAST_GLOBAL_CONNECTIONS ? "all MaxScale" : "router");
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for (SRWBackendList::const_iterator it = backends.begin(); it != backends.end(); it++)
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{
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SERVER_REF* b = (*it)->backend();
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switch (criteria)
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{
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case LEAST_GLOBAL_CONNECTIONS:
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MXS_INFO("MaxScale connections : %d in \t[%s]:%d %s",
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b->server->stats.n_current, b->server->name,
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b->server->port, STRSRVSTATUS(b->server));
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break;
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case LEAST_ROUTER_CONNECTIONS:
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MXS_INFO("RWSplit connections : %d in \t[%s]:%d %s",
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b->connections, b->server->name,
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b->server->port, STRSRVSTATUS(b->server));
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break;
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case LEAST_CURRENT_OPERATIONS:
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MXS_INFO("current operations : %d in \t[%s]:%d %s",
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b->server->stats.n_current_ops,
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b->server->name, b->server->port,
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STRSRVSTATUS(b->server));
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break;
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case LEAST_BEHIND_MASTER:
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MXS_INFO("replication lag : %d in \t[%s]:%d %s",
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b->server->rlag, b->server->name,
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b->server->port, STRSRVSTATUS(b->server));
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break;
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default:
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ss_dassert(!true);
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break;
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}
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}
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}
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SRWBackend get_root_master(const SRWBackendList& backends)
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{
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SRWBackend master;
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for (auto it = backends.begin(); it != backends.end(); it++)
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{
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auto b = *it;
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if (b->is_master() && (!master || b->server()->depth < master->server()->depth))
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{
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master = b;
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}
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}
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return master;
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}
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std::pair<int, int> get_slave_counts(SRWBackendList& backends, SRWBackend& master)
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{
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int slaves_found = 0;
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int slaves_connected = 0;
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/** Calculate how many connections we already have */
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for (SRWBackendList::const_iterator it = backends.begin(); it != backends.end(); it++)
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{
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const SRWBackend& backend = *it;
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if (backend->can_connect() && valid_for_slave(backend, master))
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{
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slaves_found += 1;
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if (backend->in_use())
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{
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slaves_connected += 1;
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}
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}
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}
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return std::make_pair(slaves_found, slaves_connected);
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}
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/**
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* Select and connect to backend servers
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*
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* @param inst Router instance
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* @param session Client session
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* @param backends List of backend servers
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* @param current_master The current master server
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* @param sescmd_list List of session commands to execute
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* @param expected_responses Pointer where number of expected responses are written
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* @param type Connection type, ALL for all types, SLAVE for slaves only
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*
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* @return True if session can continue
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*/
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bool RWSplit::select_connect_backend_servers(MXS_SESSION *session,
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SRWBackendList& backends,
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SRWBackend& current_master,
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SessionCommandList* sescmd_list,
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int* expected_responses,
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connection_type type)
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{
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SRWBackend master = get_root_master(backends);
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if (!master && config().master_failure_mode == RW_FAIL_INSTANTLY)
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{
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MXS_ERROR("Couldn't find suitable Master from %lu candidates.", backends.size());
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return false;
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}
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/** Check slave selection criteria and set compare function */
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select_criteria_t select_criteria = config().slave_selection_criteria;
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auto cmpfun = criteria_cmpfun[select_criteria];
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ss_dassert(cmpfun);
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if (MXS_LOG_PRIORITY_IS_ENABLED(LOG_INFO))
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{
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log_server_connections(select_criteria, backends);
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}
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if (type == ALL)
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{
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/** Find a master server */
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for (SRWBackendList::const_iterator it = backends.begin(); it != backends.end(); it++)
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{
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const SRWBackend& backend = *it;
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if (backend->can_connect() && master && backend == master)
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{
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if (backend->connect(session))
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{
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MXS_INFO("Selected Master: %s", backend->name());
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current_master = backend;
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}
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break;
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}
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}
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}
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auto counts = get_slave_counts(backends, master);
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int slaves_connected = counts.second;
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int max_nslaves = max_slave_count();
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ss_dassert(slaves_connected < max_nslaves || max_nslaves == 0);
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/** Connect to all possible slaves */
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for (SRWBackend backend(get_slave_candidate(backends, master, cmpfun));
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backend && slaves_connected < max_nslaves;
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backend = get_slave_candidate(backends, master, cmpfun))
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{
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if (backend->can_connect() && backend->connect(session, sescmd_list))
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{
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MXS_INFO("Selected Slave: %s", backend->name());
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if (sescmd_list && sescmd_list->size() && expected_responses)
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{
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(*expected_responses)++;
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}
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slaves_connected++;
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}
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}
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return true;
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}
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