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Readwritesplit: Graceful maintenance mode

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By allowing transactions to the master to end even if the server is in
maintenance mode makes it possible to terminate connections at a known
point. This helps prevent interrupted transactions which can help reduce
errors that are visible to the clients.
This commit is contained in:
Markus Mäkelä 2019-04-02 10:18:33 +03:00
parent 319d9fa1c5
commit 5242cd5ebf
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GPG Key ID: 72D48FCE664F7B19
4 changed files with 33 additions and 5 deletions
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19
server/modules/routing/readwritesplit/readwritesplit.hh
View File

@ -386,6 +386,25 @@ static inline const char* failure_mode_to_str(enum failure_mode type)
void closed_session_reply(GWBUF* querybuf);
bool send_readonly_error(DCB* dcb);
/**
* See if the current master is still a valid TARGET_MASTER candidate
*
* The master is valid if it's in `Master, Running` state or if it is still in but in maintenance mode while a
* transaction is open. If a transaction is open to a master in maintenance mode, the connection is closed on
* the next COMMIT or ROLLBACK.
*
* @see RWSplitSession::close_stale_connections()
*/
inline bool can_continue_using_master(const mxs::RWBackend* current_master)
{
constexpr uint64_t bits = SERVER_MASTER | SERVER_RUNNING | SERVER_MAINT;
auto server = current_master->server();
return server->is_master() || (current_master->in_use()
&& (server->status & bits) == bits
&& session_trx_is_active(current_master->dcb()->session));
}
mxs::RWBackend* get_root_master(const mxs::PRWBackends& backends, mxs::RWBackend* current_master,
const BackendSelectFunction& func);

2
server/modules/routing/readwritesplit/rwsplit_route_stmt.cc
View File

@ -638,7 +638,7 @@ RWBackend* RWSplitSession::get_master_backend()
{
if (master->in_use() || (m_config.master_reconnection && master->can_connect()))
{
if (master->is_master())
if (can_continue_using_master(master))
{
rval = master;
}

2
server/modules/routing/readwritesplit/rwsplit_select_backends.cc
View File

@ -395,7 +395,7 @@ static void log_server_connections(select_criteria_t criteria, const PRWBackends
RWBackend* get_root_master(const PRWBackends& backends, RWBackend* current_master,
const BackendSelectFunction& func)
{
if (current_master && current_master->in_use() && current_master->is_master())
if (current_master && current_master->in_use() && can_continue_using_master(current_master))
{
return current_master;
}

15
server/modules/routing/readwritesplit/rwsplitsession.cc
View File

@ -541,7 +541,7 @@ void RWSplitSession::close_stale_connections()
{
auto current_rank = get_current_rank();
for (auto& backend : m_backends)
for (auto& backend : m_raw_backends)
{
if (backend->in_use())
{
@ -549,8 +549,17 @@ void RWSplitSession::close_stale_connections()
if (!server->is_usable())
{
MXS_INFO("Discarding connection to '%s': Server is in maintenance", backend->name());
backend->close();
if (backend == m_current_master
&& can_continue_using_master(m_current_master)
&& !session_trx_is_ending(m_client->session))
{
MXS_INFO("Keeping connection to '%s' open until transaction ends", backend->name());
}
else
{
MXS_INFO("Discarding connection to '%s': Server is in maintenance", backend->name());
backend->close();
}
}
else if (server->rank() != current_rank)
{