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MXS-1503: Refactor slave selection

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Refactored and cleaned up the slave selection in preparation of
reconnection code unification.
This commit is contained in:
Markus Mäkelä 2018-03-28 12:22:11 +03:00
parent 876187b340
commit 9c7578272c
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GPG Key ID: 72D48FCE664F7B19
1 changed files with 33 additions and 69 deletions
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102
server/modules/routing/readwritesplit/rwsplit_route_stmt.cc
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@ -343,6 +343,16 @@ bool route_session_write(RWSplitSession *rses, GWBUF *querybuf,
return nsucc;
}
/**
* Check if replication lag is below acceptable levels
*/
static inline bool rpl_lag_is_ok(SRWBackend& backend, int max_rlag)
{
return max_rlag == MAX_RLAG_UNDEFINED ||
(backend->server()->rlag != MAX_RLAG_NOT_AVAILABLE &&
backend->server()->rlag <= max_rlag);
}
/**
* Provide the router with a reference to a suitable backend
*
@ -396,84 +406,38 @@ SRWBackend get_target_backend(RWSplitSession *rses, backend_type_t btype,
if (btype == BE_SLAVE)
{
for (SRWBackendList::iterator it = rses->backends.begin();
it != rses->backends.end(); it++)
for (auto it = rses->backends.begin(); it != rses->backends.end(); it++)
{
SRWBackend& backend = *it;
auto& backend = *it;
/**
* Unused backend or backend which is not master nor
* slave can't be used
*/
if (!backend->in_use() ||
(!backend->is_master() && !backend->is_slave()))
if (backend->in_use() && // Backend is in use
(backend->is_master() || backend->is_slave()) && // Either a master or a slave
rpl_lag_is_ok(backend, max_rlag)) // Not lagging too much
{
continue;
}
/**
* If there are no candidates yet accept both master or
* slave.
*/
else if (!rval)
{
/**
* Ensure that master has not changed during
* session and abort if it has.
*/
if (backend->is_master() && backend == rses->current_master)
if (!rval)
{
/** found master */
rval = backend;
}
/**
* Ensure that max replication lag is not set
* or that candidate's lag doesn't exceed the
* maximum allowed replication lag.
*/
else if (max_rlag == MAX_RLAG_UNDEFINED ||
(backend->server()->rlag != MAX_RLAG_NOT_AVAILABLE &&
backend->server()->rlag <= max_rlag))
{
/** found slave */
rval = backend;
}
}
/**
* If candidate is master, any slave which doesn't break
* replication lag limits replaces it.
*/
else if (rval->is_master() && backend->is_slave() &&
(max_rlag == MAX_RLAG_UNDEFINED ||
(backend->server()->rlag != MAX_RLAG_NOT_AVAILABLE &&
backend->server()->rlag <= max_rlag)) &&
!rses->rses_config.master_accept_reads)
{
/** found slave */
rval = backend;
}
/**
* When candidate exists, compare it against the current
* backend and update assign it to new candidate if
* necessary.
*/
else if (backend->is_slave() ||
(rses->rses_config.master_accept_reads &&
backend->is_master()))
{
if (max_rlag == MAX_RLAG_UNDEFINED ||
(backend->server()->rlag != MAX_RLAG_NOT_AVAILABLE &&
backend->server()->rlag <= max_rlag))
{
rval = compare_backends(rval, backend, rses->rses_config.slave_selection_criteria);
// No previous candidate, accept any valid server (includes master)
if ((backend->is_master() && backend == rses->current_master) ||
backend->is_slave())
{
rval = backend;
}
}
else
{
MXS_INFO("Server %s is too much behind the master "
"(%d seconds) and can't be chosen",
backend->uri(), backend->server()->rlag);
if (!rses->rses_config.master_accept_reads && rval->is_master())
{
// Pick slaves over masters with master_accept_reads=false
rval = backend;
}
else
{
// Compare the two servers and pick the best one
rval = compare_backends(rval, backend, rses->rses_config.slave_selection_criteria);
}
}
}
} /*< for */
}
}
/**
* If target was originally master only then the execution jumps