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HintRouter: Support various hint types, round-robin rotate slaves

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Supports hint types:
-master
-slave
-named server
-all

A default action, which is performed when no hint exists or on error,
can be set. The different actions are analogous to the hint types.

A maximum connection number for slaves can be set. If more slaves are
configured for the service, the filter will rotate slaves for new sessions.

Within a session with multiple slaves, the "route_to_slave"-hint will
also rotate among the slave backends.
This commit is contained in:
Esa Korhonen
2017-03-27 10:07:51 +03:00
parent ddcd1f960c
commit 90c249a8b2
5 changed files with 377 additions and 93 deletions
Download Patch File Download Diff File Expand all files Collapse all files

251
server/modules/routing/hintrouter/hintroutersession.cc
View File

@ -13,19 +13,25 @@
#define MXS_MODULE_NAME "hintrouter"
#include "hintroutersession.hh"
#include <algorithm>
#include <functional>
#include <maxscale/alloc.h>
#include "hintrouter.hh"
HintRouterSession::HintRouterSession(MXS_SESSION* pSession,
HintRouter* pRouter,
const Backends& backends)
const BackendMap& backends)
: maxscale::RouterSession(pSession)
, m_pRouter(pRouter)
, m_router(pRouter)
, m_backends(backends)
, m_master(NULL)
, m_n_routed_to_slave(0)
, m_surplus_replies(0)
{
HR_ENTRY();
update_connections();
}
@ -38,6 +44,8 @@ HintRouterSession::~HintRouterSession()
void HintRouterSession::close()
{
HR_ENTRY();
m_master = Dcb(NULL);
m_slaves.clear();
m_backends.clear();
}
@ -48,18 +56,17 @@ namespace
* Writer is a function object that writes a clone of a provided GWBUF,
* to each dcb it is called with.
*/
class Writer : std::unary_function<Dcb, bool>
class Writer : std::unary_function<HintRouterSession::MapElement, bool>
{
public:
Writer(GWBUF* pPacket)
: m_pPacket(pPacket)
{
}
{}
bool operator()(Dcb& dcb)
bool operator()(HintRouterSession::MapElement& elem)
{
bool rv = false;
Dcb& dcb = elem.second;
GWBUF* pPacket = gwbuf_clone(m_pPacket);
if (pPacket)
@ -77,7 +84,6 @@ private:
GWBUF* m_pPacket;
};
/**
* HintMatcher is a function object that when invoked with a dcb, checks
* whether the dcb matches the hint(s) that was given when the HintMatcher
@ -88,8 +94,7 @@ class HintMatcher : std::unary_function<const Dcb, bool>
public:
HintMatcher(HINT* pHint)
: m_pHint(pHint)
{
}
{}
bool operator()(const Dcb& dcb)
{
@ -151,61 +156,178 @@ private:
}
bool HintRouterSession::route_to_slave(GWBUF* pPacket)
{
bool success = false;
// Find a valid slave
size_type size = m_slaves.size();
size_type begin = m_n_routed_to_slave % size;
size_type limit = begin + size;
for (size_type curr = begin; curr != limit; curr++)
{
Dcb& candidate = m_slaves.at(curr % size);
if (SERVER_IS_SLAVE(candidate.server()))
{
success = candidate.write(pPacket);
if (success)
{
break;
}
}
}
/* It is (in theory) possible, that none of the slaves in the slave-array are
* working (or have been promoted to master) and the previous master is now
* a slave. In this situation, re-arranging the dcb:s will help. */
if (!success)
{
update_connections();
for (size_type curr = begin; curr != limit; curr++)
{
Dcb& candidate = m_slaves.at(curr % size);
success = candidate.write(pPacket);
if (success)
{
break;
}
}
}
if (success)
{
m_n_routed_to_slave++;
}
return success;
}
bool HintRouterSession::route_by_hint(GWBUF* pPacket, HINT* hint, bool ignore_errors)
{
bool success = false;
switch (hint->type)
{
case HINT_ROUTE_TO_MASTER:
if (m_master.get())
{
// The master server should be already known, but may have changed
if (SERVER_IS_MASTER(m_master.server()))
{
success = m_master.write(pPacket);
}
else
{
update_connections();
if (m_master.get())
{
HR_DEBUG("Writing packet to %s.", m_master.server()->name);
success = m_master.write(pPacket);
}
}
}
else if (!ignore_errors)
{
MXS_ERROR("Hint suggests routing to master when no master connected.");
}
break;
case HINT_ROUTE_TO_SLAVE:
if (m_slaves.size())
{
success = route_to_slave(pPacket);
}
else if (!ignore_errors)
{
MXS_ERROR("Hint suggests routing to slave when no slave connected.");
}
break;
case HINT_ROUTE_TO_NAMED_SERVER:
{
string backend_name((hint->data) ? (const char*)(hint->data) : "");
BackendMap::const_iterator iter = m_backends.find(backend_name);
if (iter != m_backends.end())
{
HR_DEBUG("Writing packet to %s.", iter->second.server()->unique_name);
success = iter->second.write(pPacket);
}
else if (!ignore_errors)
{
MXS_ERROR("Hint suggests routing to backend '%s' when no such backend connected.",
backend_name.c_str());
}
}
break;
case HINT_ROUTE_TO_ALL:
{
HR_DEBUG("Writing packet to %lu backends.", m_backends.size());
size_type n_writes =
std::count_if(m_backends.begin(), m_backends.end(), Writer(pPacket));
if (n_writes != 0)
{
m_surplus_replies = n_writes - 1;
}
else if (!ignore_errors)
{
MXS_ERROR("Nothing could be written, terminating session.");
}
success = (n_writes == m_backends.size()); // Is this too strict?
if (success)
{
gwbuf_free(pPacket);
}
}
break;
default:
MXS_ERROR("Unsupported hint type '%d'", hint->type);
break;
}
return success;
}
int32_t HintRouterSession::routeQuery(GWBUF* pPacket)
{
HR_ENTRY();
int32_t continue_routing = 1;
bool success = false;
if (pPacket->hint)
{
// At least one hint => look for match.
/* At least one hint => look for match. Only use the later hints if the
* first is unsuccessful. */
HINT* current_hint = pPacket->hint;
HR_DEBUG("Hint, looking for match.");
Backends::iterator i = std::find_if(m_backends.begin(),
m_backends.end(),
HintMatcher(pPacket->hint));
if (i != m_backends.end())
while (!success && current_hint)
{
Dcb& dcb = *i;
HR_DEBUG("Writing packet to %s.", dcb.server()->name);
dcb.write(pPacket);
// Rotate dcbs so that we get round robin as far as the slaves are concerned.
m_backends.push_front(m_backends.back()); // Push last to first
m_backends.pop_back(); // Remove last element
m_surplus_replies = 0;
}
else
{
MXS_ERROR("No backend to write to.");
continue_routing = 0;
success = route_by_hint(pPacket, current_hint, true);
current_hint = current_hint->next;
}
}
else
if (!success)
{
// No hint => all.
HR_DEBUG("No hints, writing to all.");
size_t n_writes = std::count_if(m_backends.begin(), m_backends.end(), Writer(pPacket));
gwbuf_free(pPacket);
if (n_writes != 0)
// No hint => default action.
HR_DEBUG("No hints or hint-based routing failed, falling back to default action.");
HINT fake_hint = {};
fake_hint.type = m_router->get_default_action();
if (fake_hint.type == HINT_ROUTE_TO_NAMED_SERVER)
{
m_surplus_replies = n_writes - 1;
fake_hint.data = MXS_STRDUP(m_router->get_default_server().c_str());
// Ignore allocation error, it will just result in an error later on
}
else
success = route_by_hint(pPacket, &fake_hint, false);
if (fake_hint.type == HINT_ROUTE_TO_NAMED_SERVER)
{
MXS_ERROR("Nothing could be written, terminating session.");
continue_routing = 0;
MXS_FREE(fake_hint.data);
}
}
return continue_routing;
if (!success)
{
gwbuf_free(pPacket);
}
return success;
}
@ -217,20 +339,19 @@ void HintRouterSession::clientReply(GWBUF* pPacket, DCB* pBackend)
if (m_surplus_replies == 0)
{
HR_DEBUG("Returning packet from %s.", pServer ? pServer->name : "(null)");
HR_DEBUG("Returning packet from %s.", pServer ? pServer->unique_name : "(null)");
MXS_SESSION_ROUTE_REPLY(pBackend->session, pPacket);
}
else
{
HR_DEBUG("Ignoring reply packet from %s.", pServer ? pServer->name : "(null)");
HR_DEBUG("Ignoring reply packet from %s.", pServer ? pServer->unique_name : "(null)");
--m_surplus_replies;
gwbuf_free(pPacket);
}
}
void HintRouterSession::handleError(GWBUF* pMessage,
DCB* pProblem,
mxs_error_action_t action,
@ -274,3 +395,33 @@ void HintRouterSession::handleError(GWBUF* pMessage,
*pSuccess = false;
}
}
void HintRouterSession::update_connections()
{
/* Attempt to rearrange the dcb:s in the session such that the master and
* slave containers are correct again. Do not try to make new connections,
* since those would not have the correct session state anyways. */
m_master = Dcb(NULL);
m_slaves.clear();
for (BackendMap::const_iterator iter = m_backends.begin();
iter != m_backends.end(); iter++)
{
SERVER* server = iter->second.get()->server;
if (SERVER_IS_MASTER(server))
{
if (!m_master.get())
{
m_master = iter->second;
}
else
{
MXS_WARNING("Found multiple master servers when updating connections.");
}
}
else if (SERVER_IS_SLAVE(server))
{
m_slaves.push_back(iter->second);
}
}
}