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Move MXS-807 refactor read-write split into develop.

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counterpoint
2016-09-20 11:55:02 +01:00
parent 3992135325
commit 923761159f
8 changed files with 4066 additions and 3620 deletions
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server/modules/routing/readwritesplit/rwsplit_select_backends.c Normal file
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/*
* Copyright (c) 2016 MariaDB Corporation Ab
*
* Use of this software is governed by the Business Source License included
* in the LICENSE.TXT file and at www.mariadb.com/bsl.
*
* Change Date: 2019-01-01
*
* On the date above, in accordance with the Business Source License, use
* of this software will be governed by version 2 or later of the General
* Public License.
*/
#include <stdio.h>
#include <strings.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <router.h>
#include <readwritesplit.h>
#include <rwsplit_internal.h>
/**
* @file rwsplit_select_backends.c The functions that implement back end
* selection for the read write split router. All of these functions are
* internal to that router and not intended to be called from elsewhere.
*
* @verbatim
* Revision History
*
* Date Who Description
* 08/08/2016 Martin Brampton Initial implementation
*
* @endverbatim
*/
static bool connect_server(backend_ref_t *bref, SESSION *session, bool execute_history);
static void log_server_connections(select_criteria_t select_criteria,
backend_ref_t *backend_ref, int router_nservers);
static BACKEND *get_root_master(backend_ref_t *servers, int router_nservers);
static int bref_cmp_global_conn(const void *bref1, const void *bref2);
static int bref_cmp_router_conn(const void *bref1, const void *bref2);
static int bref_cmp_behind_master(const void *bref1, const void *bref2);
static int bref_cmp_current_load(const void *bref1, const void *bref2);
/**
* The order of functions _must_ match with the order the select criteria are
* listed in select_criteria_t definition in readwritesplit.h
*/
int (*criteria_cmpfun[LAST_CRITERIA])(const void *, const void *) =
{
NULL,
bref_cmp_global_conn,
bref_cmp_router_conn,
bref_cmp_behind_master,
bref_cmp_current_load
};
/*
* The following function is the only one that is called from elsewhere in
* the read write split router. It is not intended for use from outside this
* router. Other functions in this module are internal and are called
* directly or indirectly by this function.
*/
/**
* @brief Search suitable backend servers from those of router instance
*
* It is assumed that there is only one master among servers of a router instance.
* As a result, the first master found is chosen. There will possibly be more
* backend references than connected backends because only those in correct state
* are connected to.
*
* @param p_master_ref Pointer to location where master's backend reference is to be stored
* @param backend_ref Pointer to backend server reference object array
* @param router_nservers Number of backend server pointers pointed to by @p backend_ref
* @param max_nslaves Upper limit for the number of slaves
* @param max_slave_rlag Maximum allowed replication lag for any slave
* @param select_criteria Slave selection criteria
* @param session Client session
* @param router Router instance
* @return true, if at least one master and one slave was found.
*/
bool select_connect_backend_servers(backend_ref_t **p_master_ref,
backend_ref_t *backend_ref,
int router_nservers, int max_nslaves,
int max_slave_rlag,
select_criteria_t select_criteria,
SESSION *session,
ROUTER_INSTANCE *router)
{
if (p_master_ref == NULL || backend_ref == NULL)
{
MXS_ERROR("Master reference (%p) or backend reference (%p) is NULL.",
p_master_ref, backend_ref);
ss_dassert(false);
return false;
}
/* get the root Master */
BACKEND *master_host = get_root_master(backend_ref, router_nservers);
if (router->rwsplit_config.rw_master_failure_mode == RW_FAIL_INSTANTLY &&
(master_host == NULL || SERVER_IS_DOWN(master_host->backend_server)))
{
MXS_ERROR("Couldn't find suitable Master from %d candidates.", router_nservers);
return false;
}
/**
* Existing session : master is already chosen and connected.
* The function was called because new slave must be selected to replace
* failed one.
*/
bool master_connected = *p_master_ref != NULL;
/** Check slave selection criteria and set compare function */
int (*p)(const void *, const void *) = criteria_cmpfun[select_criteria];
ss_dassert(p);
/** Sort the pointer list to servers according to slave selection criteria.
* The servers that match the criteria the best are at the beginning of
* the list. */
qsort(backend_ref, (size_t) router_nservers, sizeof(backend_ref_t), p);
if (MXS_LOG_PRIORITY_IS_ENABLED(LOG_INFO))
{
log_server_connections(select_criteria, backend_ref, router_nservers);
}
int slaves_found = 0;
int slaves_connected = 0;
const int min_nslaves = 0; /*< not configurable at the time */
bool succp = false;
/**
* Choose at least 1+min_nslaves (master and slave) and at most 1+max_nslaves
* servers from the sorted list. First master found is selected.
*/
for (int i = 0; i < router_nservers &&
(slaves_connected < max_nslaves || !master_connected); i++)
{
SERVER *serv = backend_ref[i].bref_backend->backend_server;
if (!BREF_HAS_FAILED(&backend_ref[i]) && SERVER_IS_RUNNING(serv))
{
/* check also for relay servers and don't take the master_host */
if (slaves_found < max_nslaves &&
(max_slave_rlag == MAX_RLAG_UNDEFINED ||
(serv->rlag != MAX_RLAG_NOT_AVAILABLE &&
serv->rlag <= max_slave_rlag)) &&
(SERVER_IS_SLAVE(serv) || SERVER_IS_RELAY_SERVER(serv)) &&
(master_host == NULL || (serv != master_host->backend_server)))
{
slaves_found += 1;
if (BREF_IS_IN_USE((&backend_ref[i])) ||
connect_server(&backend_ref[i], session, true))
{
slaves_connected += 1;
}
}
/* take the master_host for master */
else if (master_host && (serv == master_host->backend_server))
{
/** p_master_ref must be assigned with this backend_ref pointer
* because its original value may have been lost when backend
* references were sorted with qsort. */
*p_master_ref = &backend_ref[i];
if (!master_connected)
{
if (connect_server(&backend_ref[i], session, false))
{
master_connected = true;
}
}
}
}
} /*< for */
/**
* Successful cases
*/
if (slaves_connected >= min_nslaves && slaves_connected <= max_nslaves)
{
succp = true;
if (MXS_LOG_PRIORITY_IS_ENABLED(LOG_INFO))
{
if (slaves_connected < max_nslaves)
{
MXS_INFO("Couldn't connect to maximum number of "
"slaves. Connected successfully to %d slaves "
"of %d of them.", slaves_connected, slaves_found);
}
for (int i = 0; i < router_nservers; i++)
{
if (BREF_IS_IN_USE((&backend_ref[i])))
{
MXS_INFO("Selected %s in \t%s:%d",
STRSRVSTATUS(backend_ref[i].bref_backend->backend_server),
backend_ref[i].bref_backend->backend_server->name,
backend_ref[i].bref_backend->backend_server->port);
}
} /* for */
}
}
/** Failure cases */
else
{
if (slaves_connected < min_nslaves)
{
MXS_ERROR("Couldn't establish required amount of "
"slave connections for router session.");
}
/** Clean up connections */
for (int i = 0; i < router_nservers; i++)
{
if (BREF_IS_IN_USE((&backend_ref[i])))
{
ss_dassert(backend_ref[i].bref_backend->backend_conn_count > 0);
/** disconnect opened connections */
bref_clear_state(&backend_ref[i], BREF_IN_USE);
/** Decrease backend's connection counter. */
atomic_add(&backend_ref[i].bref_backend->backend_conn_count, -1);
dcb_close(backend_ref[i].bref_dcb);
}
}
}
return succp;
}
/** Compare number of connections from this router in backend servers */
static int bref_cmp_router_conn(const void *bref1, const void *bref2)
{
BACKEND *b1 = ((backend_ref_t *)bref1)->bref_backend;
BACKEND *b2 = ((backend_ref_t *)bref2)->bref_backend;
if (b1->weight == 0 && b2->weight == 0)
{
return b1->backend_server->stats.n_current -
b2->backend_server->stats.n_current;
}
else if (b1->weight == 0)
{
return 1;
}
else if (b2->weight == 0)
{
return -1;
}
return ((1000 + 1000 * b1->backend_conn_count) / b1->weight) -
((1000 + 1000 * b2->backend_conn_count) / b2->weight);
}
/** Compare number of global connections in backend servers */
static int bref_cmp_global_conn(const void *bref1, const void *bref2)
{
BACKEND *b1 = ((backend_ref_t *)bref1)->bref_backend;
BACKEND *b2 = ((backend_ref_t *)bref2)->bref_backend;
if (b1->weight == 0 && b2->weight == 0)
{
return b1->backend_server->stats.n_current -
b2->backend_server->stats.n_current;
}
else if (b1->weight == 0)
{
return 1;
}
else if (b2->weight == 0)
{
return -1;
}
return ((1000 + 1000 * b1->backend_server->stats.n_current) / b1->weight) -
((1000 + 1000 * b2->backend_server->stats.n_current) / b2->weight);
}
/** Compare replication lag between backend servers */
static int bref_cmp_behind_master(const void *bref1, const void *bref2)
{
BACKEND *b1 = ((backend_ref_t *)bref1)->bref_backend;
BACKEND *b2 = ((backend_ref_t *)bref2)->bref_backend;
return ((b1->backend_server->rlag < b2->backend_server->rlag) ? -1
: ((b1->backend_server->rlag > b2->backend_server->rlag) ? 1 : 0));
}
/** Compare number of current operations in backend servers */
static int bref_cmp_current_load(const void *bref1, const void *bref2)
{
SERVER *s1 = ((backend_ref_t *)bref1)->bref_backend->backend_server;
SERVER *s2 = ((backend_ref_t *)bref2)->bref_backend->backend_server;
BACKEND *b1 = ((backend_ref_t *)bref1)->bref_backend;
BACKEND *b2 = ((backend_ref_t *)bref2)->bref_backend;
if (b1->weight == 0 && b2->weight == 0)
{
return b1->backend_server->stats.n_current -
b2->backend_server->stats.n_current;
}
else if (b1->weight == 0)
{
return 1;
}
else if (b2->weight == 0)
{
return -1;
}
return ((1000 * s1->stats.n_current_ops) - b1->weight) -
((1000 * s2->stats.n_current_ops) - b2->weight);
}
/**
* @brief Connect a server
*
* Connects to a server, adds callbacks to the created DCB and updates
* router statistics. If @p execute_history is true, the session command
* history will be executed on this server.
*
* @param b Router's backend structure for the server
* @param session Client's session object
* @param execute_history Execute session command history
* @return True if successful, false if an error occurred
*/
static bool connect_server(backend_ref_t *bref, SESSION *session, bool execute_history)
{
SERVER *serv = bref->bref_backend->backend_server;
bool rval = false;
bref->bref_dcb = dcb_connect(serv, session, serv->protocol);
if (bref->bref_dcb != NULL)
{
if (!execute_history || execute_sescmd_history(bref))
{
/** Add a callback for unresponsive server */
dcb_add_callback(bref->bref_dcb, DCB_REASON_NOT_RESPONDING,
&router_handle_state_switch, (void *) bref);
bref->bref_state = 0;
bref_set_state(bref, BREF_IN_USE);
atomic_add(&bref->bref_backend->backend_conn_count, 1);
rval = true;
}
else
{
MXS_ERROR("Failed to execute session command in %s (%s:%d). See earlier "
"errors for more details.",
bref->bref_backend->backend_server->unique_name,
bref->bref_backend->backend_server->name,
bref->bref_backend->backend_server->port);
dcb_close(bref->bref_dcb);
bref->bref_dcb = NULL;
}
}
else
{
MXS_ERROR("Unable to establish connection with server %s:%d",
serv->name, serv->port);
}
return rval;
}
/**
* @brief Log server connections
*
* @param select_criteria Slave selection criteria
* @param backend_ref Backend reference array
* @param router_nservers Number of backends in @p backend_ref
*/
static void log_server_connections(select_criteria_t select_criteria,
backend_ref_t *backend_ref, int router_nservers)
{
if (select_criteria == LEAST_GLOBAL_CONNECTIONS ||
select_criteria == LEAST_ROUTER_CONNECTIONS ||
select_criteria == LEAST_BEHIND_MASTER ||
select_criteria == LEAST_CURRENT_OPERATIONS)
{
MXS_INFO("Servers and %s connection counts:",
select_criteria == LEAST_GLOBAL_CONNECTIONS ? "all MaxScale"
: "router");
for (int i = 0; i < router_nservers; i++)
{
BACKEND *b = backend_ref[i].bref_backend;
switch (select_criteria)
{
case LEAST_GLOBAL_CONNECTIONS:
MXS_INFO("MaxScale connections : %d in \t%s:%d %s",
b->backend_server->stats.n_current, b->backend_server->name,
b->backend_server->port, STRSRVSTATUS(b->backend_server));
break;
case LEAST_ROUTER_CONNECTIONS:
MXS_INFO("RWSplit connections : %d in \t%s:%d %s",
b->backend_conn_count, b->backend_server->name,
b->backend_server->port, STRSRVSTATUS(b->backend_server));
break;
case LEAST_CURRENT_OPERATIONS:
MXS_INFO("current operations : %d in \t%s:%d %s",
b->backend_server->stats.n_current_ops,
b->backend_server->name, b->backend_server->port,
STRSRVSTATUS(b->backend_server));
break;
case LEAST_BEHIND_MASTER:
MXS_INFO("replication lag : %d in \t%s:%d %s",
b->backend_server->rlag, b->backend_server->name,
b->backend_server->port, STRSRVSTATUS(b->backend_server));
default:
break;
}
}
}
}
/********************************
* This routine returns the root master server from MySQL replication tree
* Get the root Master rule:
*
* find server with the lowest replication depth level
* and the SERVER_MASTER bitval
* Servers are checked even if they are in 'maintenance'
*
* @param servers The list of servers
* @param router_nservers The number of servers
* @return The Master found
*
*/
static BACKEND *get_root_master(backend_ref_t *servers, int router_nservers)
{
int i = 0;
BACKEND *master_host = NULL;
for (i = 0; i < router_nservers; i++)
{
BACKEND *b;
if (servers[i].bref_backend == NULL)
{
continue;
}
b = servers[i].bref_backend;
if ((b->backend_server->status & (SERVER_MASTER | SERVER_MAINT)) ==
SERVER_MASTER)
{
if (master_host == NULL ||
(b->backend_server->depth < master_host->backend_server->depth))
{
master_host = b;
}
}
}
return master_host;
}