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MXS-2464: Retry failed session commands

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If the execution of a session command fails on a master, it is retried
again. If the master is not available, the response will be returned from
one of the slaves.
This commit is contained in:
Markus Mäkelä 2019-05-31 09:01:39 +03:00
parent 6d089e3283
commit 220fea3546
No known key found for this signature in database
GPG Key ID: 72D48FCE664F7B19
2 changed files with 42 additions and 3 deletions
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44
server/modules/routing/readwritesplit/rwsplitsession.cc
View File

@ -747,6 +747,7 @@ void RWSplitSession::clientReply(GWBUF* writebuf, DCB* backend_dcb)
// Backend is still in use and has more session commands to execute
if (backend->execute_session_command() && backend->is_waiting_result())
{
MXS_INFO("%lu session commands left on '%s'", backend->session_command_count(), backend->name());
m_expected_responses++;
}
}
@ -881,6 +882,44 @@ bool RWSplitSession::start_trx_replay()
return rval;
}
bool RWSplitSession::retry_master_query(SRWBackend& backend)
{
bool can_continue = false;
if (backend->has_session_commands())
{
// Try to route the session command again. If the master is not available, the response will be
// returned from one of the slaves.
mxb_assert(!m_current_query.get());
mxb_assert(!m_sescmd_list.empty());
mxb_assert(m_sescmd_count >= 2);
MXS_INFO("Retrying session command due to master failure: %s",
backend->next_session_command()->to_string().c_str());
// Before routing it, pop the failed session command off the list and decrement the number of
// executed session commands. This "overwrites" the existing command and prevents history duplication.
m_sescmd_list.pop_back();
--m_sescmd_count;
retry_query(backend->next_session_command()->deep_copy_buffer());
can_continue = true;
}
else if (m_current_query.get())
{
retry_query(m_current_query.release());
can_continue = true;
}
else
{
// This should never happen
mxb_assert_message(!true, "m_current_query is empty and no session commands being executed");
MXS_ERROR("Current query unexpectedly empty when trying to retry query on master");
}
return can_continue;
}
/**
* @brief Router error handling routine
*
@ -945,10 +984,9 @@ void RWSplitSession::handleError(GWBUF* errmsgbuf,
m_expected_responses--;
errmsg += " Lost connection to master server while waiting for a result.";
if (m_current_query.get() && can_retry_query())
if (can_retry_query())
{
can_continue = true;
retry_query(m_current_query.release());
can_continue = retry_master_query(backend);
}
else if (m_config.master_failure_mode == RW_ERROR_ON_WRITE)
{

1
server/modules/routing/readwritesplit/rwsplitsession.hh
View File

@ -225,6 +225,7 @@ private:
int get_max_replication_lag();
mxs::SRWBackend& get_backend_from_dcb(DCB* dcb);
bool retry_master_query(mxs::SRWBackend& backend);
void handle_error_reply_client(DCB* backend_dcb, GWBUF* errmsg);
bool handle_error_new_connection(DCB* backend_dcb, GWBUF* errmsg);
void manage_transactions(mxs::SRWBackend& backend, GWBUF* writebuf);