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MXS-1507: Retry interrupted queries in transactions

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As the current query was added to the transaction log before it finished,
the m_current_query contained a duplicate of the latest transaction log
entry. To correctly log only successful transactions, the statement should
be added only after it has successfully completed. This change also
removed the unnecessary cloning that took place when the statement was
added to the log before it finished.

With the fixed transaction logging, the value of m_current_query can be
stashed for later retrying while the replay process is happening. If the
replay completes successfully and the checksums match, the interrupted
query is retried.

Also added a clarifying comment to can_retry_query to explain why a query
inside a transaction cannot be retried.
This commit is contained in:
Markus Mäkelä
2018-04-19 16:10:10 +03:00
parent 01bf5cc8b0
commit c1c942a058
3 changed files with 29 additions and 27 deletions
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27
server/modules/routing/readwritesplit/rwsplitsession.cc
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@ -387,6 +387,12 @@ void RWSplitSession::handle_trx_replay()
if (chksum == m_replayed_trx.checksum())
{
MXS_INFO("Checksums match, replay successful.");
if (m_interrupted_query.get())
{
MXS_INFO("Resuming execution: %s", mxs::extract_sql(m_interrupted_query.get()).c_str());
retry_query(m_interrupted_query.release(), 0);
}
}
else
{
@ -431,12 +437,15 @@ void RWSplitSession::clientReply(GWBUF *writebuf, DCB *backend_dcb)
return;
}
m_current_query.reset();
if (session_trx_is_active(m_client->session))
{
m_trx.add_stmt(m_current_query.release());
m_trx.add_result(writebuf);
}
else
{
m_current_query.reset();
}
if (backend->reply_is_complete(writebuf))
{
@ -622,16 +631,10 @@ void RWSplitSession::handleError(GWBUF *errmsgbuf, DCB *problem_dcb,
}
else if (session_trx_is_active(session))
{
if (m_current_query.get())
{
// TODO: Re-execute interrupted queries in transactions
can_continue = false;
}
else
{
can_continue = true;
start_trx_replay();
}
// Stash any interrupted queries while we replay the transaction
m_interrupted_query.reset(m_current_query.release());
can_continue = true;
start_trx_replay();
}
*succp = can_continue;