532 lines
15 KiB
C
532 lines
15 KiB
C
/*
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* This file is distributed as part of the SkySQL Gateway. It is free
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* software: you can redistribute it and/or modify it under the terms of the
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* GNU General Public License as published by the Free Software Foundation,
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* version 2.
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*
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* This program is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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* FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
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* details.
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*
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* You should have received a copy of the GNU General Public License along with
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* this program; if not, write to the Free Software Foundation, Inc., 51
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* Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Copyright SkySQL Ab 2013
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*/
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/**
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* @file readconnroute.c - Read Connection Load Balancing Query Router
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*
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* This is the implementation of a simple query router that balances
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* read connections. It assumes the service is configured with a set
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* of slaves and that the application clients already split read and write
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* queries. It offers a service to balance the client read connections
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* over this set of slave servers. It does this once only, at the time
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* the connection is made. It chooses the server that currently has the least
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* number of connections by keeping a count for each server of how
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* many connections the query router has made to the server.
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*
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* When two servers have the same number of current connections the one with
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* the least number of connections since startup will be used.
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*
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* The router may also have options associated to it that will limit the
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* choice of backend server. Currently two options are supported, the "master"
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* option will cause the router to only connect to servers marked as masters
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* and the "slave" option will limit connections to routers that are marked
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* as slaves. If neither option is specified the router will connect to either
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* masters or slaves.
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*
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* @verbatim
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* Revision History
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*
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* Date Who Description
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* 14/06/2013 Mark Riddoch Initial implementation
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* 25/06/2013 Mark Riddoch Addition of checks for current server state
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* 26/06/2013 Mark Riddoch Use server with least connections since
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* startup if the number of current
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* connections is the same for two servers
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* Addition of master and slave options
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* 27/06/2013 Vilho Raatikka Added skygw_log_write command as an example
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* and necessary headers.
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* 17/07/2013 Massimiliano Pinto Added clientReply routine:
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* called by backend server to send data to client
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* Included mysql_client_server_protocol.h
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* with macros and MySQL commands with MYSQL_ prefix
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* avoiding any conflict with the standard ones
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* in mysql.h
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* 22/07/2013 Mark Riddoch Addition of joined router option for Galera
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* clusters
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* 31/07/2013 Massimiliano Pinto Added a check for candidate server, if NULL return
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* 12/08/2013 Mark Riddoch Log unsupported router options
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*
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* @endverbatim
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <service.h>
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#include <server.h>
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#include <router.h>
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#include <atomic.h>
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#include <spinlock.h>
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#include <readconnection.h>
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#include <dcb.h>
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#include <spinlock.h>
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#include <skygw_types.h>
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#include <skygw_utils.h>
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#include <log_manager.h>
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#include <mysql_client_server_protocol.h>
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static char *version_str = "V1.0.2";
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/* The router entry points */
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static ROUTER *createInstance(SERVICE *service, char **options);
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static void *newSession(ROUTER *instance, SESSION *session);
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static void closeSession(ROUTER *instance, void *router_session);
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static int routeQuery(ROUTER *instance, void *router_session, GWBUF *queue);
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static void diagnostics(ROUTER *instance, DCB *dcb);
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static void clientReply(
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ROUTER *instance,
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void *router_session,
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GWBUF *queue,
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DCB *backend_dcb);
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/** The module object definition */
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static ROUTER_OBJECT MyObject = {
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createInstance,
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newSession,
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closeSession,
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routeQuery,
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diagnostics,
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clientReply
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};
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static SPINLOCK instlock;
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static INSTANCE *instances;
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/**
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* Implementation of the mandatory version entry point
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*
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* @return version string of the module
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*/
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char *
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version()
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{
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return version_str;
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}
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/**
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* The module initialisation routine, called when the module
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* is first loaded.
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*/
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void
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ModuleInit()
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{
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skygw_log_write(
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LOGFILE_MESSAGE,
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"Initialise readconnroute router module %s.\n", version_str);
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spinlock_init(&instlock);
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instances = NULL;
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}
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/**
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* The module entry point routine. It is this routine that
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* must populate the structure that is referred to as the
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* "module object", this is a structure with the set of
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* external entry points for this module.
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*
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* @return The module object
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*/
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ROUTER_OBJECT *
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GetModuleObject()
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{
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return &MyObject;
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}
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/**
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* Create an instance of the router for a particular service
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* within the gateway.
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*
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* @param service The service this router is being create for
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* @param options An array of options for this query router
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*
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* @return The instance data for this new instance
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*/
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static ROUTER *
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createInstance(SERVICE *service, char **options)
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{
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INSTANCE *inst;
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SERVER *server;
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int i, n;
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if ((inst = malloc(sizeof(INSTANCE))) == NULL)
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return NULL;
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memset(&inst->stats, 0, sizeof(ROUTER_STATS));
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inst->service = service;
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spinlock_init(&inst->lock);
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inst->connections = NULL;
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/*
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* We need an array of the backend servers in the instance structure so
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* that we can maintain a count of the number of connections to each
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* backend server.
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*/
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for (server = service->databases, n = 0; server; server = server->nextdb)
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n++;
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inst->servers = (BACKEND **)calloc(n + 1, sizeof(BACKEND *));
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if (!inst->servers)
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{
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free(inst);
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return NULL;
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}
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for (server = service->databases, n = 0; server; server = server->nextdb)
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{
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if ((inst->servers[n] = malloc(sizeof(BACKEND))) == NULL)
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{
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for (i = 0; i < n; i++)
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free(inst->servers[i]);
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free(inst->servers);
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free(inst);
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return NULL;
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}
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inst->servers[n]->server = server;
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inst->servers[n]->current_connection_count = 0;
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n++;
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}
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inst->servers[n] = NULL;
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/*
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* Process the options
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*/
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inst->bitmask = 0;
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inst->bitvalue = 0;
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if (options)
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{
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for (i = 0; options[i]; i++)
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{
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if (!strcasecmp(options[i], "master"))
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{
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inst->bitmask |= (SERVER_MASTER|SERVER_SLAVE);
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inst->bitvalue |= SERVER_MASTER;
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}
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else if (!strcasecmp(options[i], "slave"))
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{
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inst->bitmask |= (SERVER_MASTER|SERVER_SLAVE);
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inst->bitvalue |= SERVER_SLAVE;
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}
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else if (!strcasecmp(options[i], "joined"))
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{
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inst->bitmask |= (SERVER_JOINED);
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inst->bitvalue |= SERVER_JOINED;
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}
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else
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{
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skygw_log_write(LOGFILE_ERROR,
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"Unsupported router option %s for "
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"readconnroute\n",
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options[i]);
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}
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}
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}
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/*
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* We have completed the creation of the instance data, so now
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* insert this router instance into the linked list of routers
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* that have been created with this module.
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*/
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spinlock_acquire(&instlock);
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inst->next = instances;
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instances = inst;
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spinlock_release(&instlock);
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return (ROUTER *)inst;
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}
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/**
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* Associate a new session with this instance of the router.
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*
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* @param instance The router instance data
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* @param session The session itself
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* @return Session specific data for this session
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*/
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static void *
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newSession(ROUTER *instance, SESSION *session)
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{
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INSTANCE *inst = (INSTANCE *)instance;
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CLIENT_SESSION *client_ses;
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BACKEND *candidate = NULL;
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int i;
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skygw_log_write_flush(
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LOGFILE_TRACE,
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"%lu [newSession] new router session with session "
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"%p, and inst %p.",
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pthread_self(),
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session,
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inst);
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if ((client_ses = (CLIENT_SESSION *)malloc(sizeof(CLIENT_SESSION))) == NULL) {
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return NULL;
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}
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/*
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* Find a backend server to connect to. This is the extent of the
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* load balancing algorithm we need to implement for this simple
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* connection router.
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*/
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/*
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* Loop over all the servers and find any that have fewer connections than our
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* candidate server.
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*
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* If a server has less connections than the current candidate we mark this
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* as the new candidate to connect to.
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*
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* If a server has the same number of connections currently as the candidate
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* and has had less connections over time than the candidate it will also
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* become the new candidate. This has the effect of spreading the connections
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* over different servers during periods of very low load.
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*/
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for (i = 0; inst->servers[i]; i++) {
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if(inst->servers[i]) {
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skygw_log_write(
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LOGFILE_TRACE,
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"Examine server in port %d with %d connections. "
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"Status is %d, "
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"inst->bitvalue is %d",
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inst->servers[i]->server->port,
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inst->servers[i]->current_connection_count,
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inst->servers[i]->server->status,
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inst->bitmask);
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}
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if (inst->servers[i] &&
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SERVER_IS_RUNNING(inst->servers[i]->server) &&
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(inst->servers[i]->server->status & inst->bitmask) == inst->bitvalue)
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{
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/* If no candidate set, set first running server as
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our initial candidate server */
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if (candidate == NULL)
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{
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candidate = inst->servers[i];
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}
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else if (inst->servers[i]->current_connection_count <
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candidate->current_connection_count)
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{
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/* This running server has fewer
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connections, set it as a new candidate */
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candidate = inst->servers[i];
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}
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else if (inst->servers[i]->current_connection_count ==
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candidate->current_connection_count &&
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inst->servers[i]->server->stats.n_connections <
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candidate->server->stats.n_connections)
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{
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/* This running server has the same number
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of connections currently as the candidate
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but has had fewer connections over time
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than candidate, set this server to candidate*/
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candidate = inst->servers[i];
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}
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}
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}
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/* no candidate server here, clean and return NULL */
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if (!candidate) {
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skygw_log_write_flush(
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LOGFILE_ERROR,
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"%lu [newSession] Couldn't find eligible candidate "
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"server. Exiting.",
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pthread_self());
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free(client_ses);
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return NULL;
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}
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/*
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* We now have the server with the least connections.
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* Bump the connection count for this server
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*/
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atomic_add(&candidate->current_connection_count, 1);
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client_ses->backend = candidate;
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skygw_log_write(
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LOGFILE_TRACE,
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"%lu [newSession] Selected server in port %d. "
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"Connections : %d\n",
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pthread_self(),
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candidate->server->port,
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candidate->current_connection_count);
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/*
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* Open a backend connection, putting the DCB for this
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* connection in the client_ses->dcb
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*/
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if ((client_ses->dcb = dcb_connect(candidate->server, session,
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candidate->server->protocol)) == NULL)
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{
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atomic_add(&candidate->current_connection_count, -1);
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skygw_log_write(
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LOGFILE_ERROR,
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"%lu [newSession] Failed to establish connection to "
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"server in port %d. Exiting.",
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pthread_self(),
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candidate->server->port);
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free(client_ses);
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return NULL;
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}
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inst->stats.n_sessions++;
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/* Add this session to the list of active sessions */
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spinlock_acquire(&inst->lock);
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client_ses->next = inst->connections;
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inst->connections = client_ses;
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spinlock_release(&inst->lock);
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return (void *)client_ses;
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}
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/**
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* Close a session with the router, this is the mechanism
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* by which a router may cleanup data structure etc.
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*
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* @param instance The router instance data
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* @param router_session The session being closed
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*/
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static void
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closeSession(ROUTER *instance, void *router_session)
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{
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INSTANCE *inst = (INSTANCE *)instance;
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CLIENT_SESSION *client_ses = (CLIENT_SESSION *)router_session;
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bool succp = FALSE;
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/*
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* Close the connection to the backend
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*/
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skygw_log_write_flush(
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LOGFILE_TRACE,
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"%lu [closeSession] closing session with "
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"router_session "
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"%p, and inst %p.",
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pthread_self(),
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client_ses,
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inst);
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succp = client_ses->dcb->func.close(client_ses->dcb);
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if (succp) {
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client_ses->dcb = NULL;
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}
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atomic_add(&client_ses->backend->current_connection_count, -1);
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atomic_add(&client_ses->backend->server->stats.n_current, -1);
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spinlock_acquire(&inst->lock);
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if (inst->connections == client_ses)
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inst->connections = client_ses->next;
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else
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{
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CLIENT_SESSION *ptr = inst->connections;
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while (ptr && ptr->next != client_ses)
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ptr = ptr->next;
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if (ptr)
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ptr->next = client_ses->next;
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}
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spinlock_release(&inst->lock);
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/*
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* We are no longer in the linked list, free
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* all the memory and other resources associated
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* to the client session.
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*/
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free(client_ses);
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}
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/**
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* We have data from the client, we must route it to the backend.
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* This is simply a case of sending it to the connection that was
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* chosen when we started the client session.
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*
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* @param instance The router instance
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* @param router_session The router session returned from the newSession call
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* @param queue The queue of data buffers to route
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* @return The number of bytes sent
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*/
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static int
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routeQuery(ROUTER *instance, void *router_session, GWBUF *queue)
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{
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INSTANCE *inst = (INSTANCE *)instance;
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CLIENT_SESSION *session = (CLIENT_SESSION *)router_session;
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uint8_t *payload = GWBUF_DATA(queue);
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int mysql_command = -1;
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inst->stats.n_queries++;
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mysql_command = MYSQL_GET_COMMAND(payload);
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switch(mysql_command) {
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case MYSQL_COM_CHANGE_USER:
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return session->dcb->func.auth(session->dcb, NULL, session->dcb->session, queue);
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default:
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return session->dcb->func.write(session->dcb, queue);
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}
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}
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/**
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* Display router diagnostics
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*
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* @param instance Instance of the router
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* @param dcb DCB to send diagnostics to
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*/
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static void
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diagnostics(ROUTER *instance, DCB *dcb)
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{
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INSTANCE *inst = (INSTANCE *)instance;
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CLIENT_SESSION *session;
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int i = 0;
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spinlock_acquire(&inst->lock);
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session = inst->connections;
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while (session)
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{
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i++;
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session = session->next;
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}
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spinlock_release(&inst->lock);
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dcb_printf(dcb, "\tNumber of router sessions: %d\n", inst->stats.n_sessions);
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dcb_printf(dcb, "\tCurrent no. of router sessions: %d\n", i);
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dcb_printf(dcb, "\tNumber of queries forwarded: %d\n", inst->stats.n_queries);
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}
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/**
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* Client Reply routine
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*
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* The routine will reply to client data from backend server
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*
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* @param instance The router instance
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* @param router_session The router session
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* @param backend_dcb The backend DCB
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* @param queue The GWBUF with reply data
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*/
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static void
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clientReply(ROUTER* instance, void* router_session, GWBUF* queue, DCB *backend_dcb)
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{
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INSTANCE* inst = NULL;
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DCB *client = NULL;
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CLIENT_SESSION* session = NULL;
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inst = (INSTANCE *)instance;
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session = (CLIENT_SESSION *)router_session;
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client = backend_dcb->session->client;
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client->func.write(client, queue);
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}
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///
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