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MXS-1777 Turn server weights to their inverses, and make them doubles.

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The math becomes simpler when the weight is inverted, i.e. a simple multiplication
to get the (inverse) score. Inverse weights are normalized to the range [0..1] where a lower
number is a higher weight,
The enum select_criteria_t is used to provide a std::function that takes the backends
as vector  (rather than the prior pairwise compares) and returns the best backend.
This commit is contained in:
Niclas Antti
2018-08-28 11:01:11 +03:00
parent 105bd7195f
commit 91acbc0994
7 changed files with 278 additions and 289 deletions
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33
server/modules/routing/readconnroute/readconnroute.cc
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@ -358,23 +358,30 @@ newSession(MXS_ROUTER *instance, MXS_SESSION *session)
{
candidate = ref;
}
else if (ref->weight == 0 || candidate->weight == 0)
else if (candidate->connections == 0)
{
candidate = ref->weight ? ref : candidate;
/* The candidate is already as good as it gets. */
}
else if (((ref->connections + 1) * 1000) / ref->weight <
((candidate->connections + 1) * 1000) / candidate->weight)
else if (ref->connections == 0)
{
/* This running server has fewer connections, set it as a new candidate */
candidate = ref;
}
else if (((ref->connections + 1) * 1000) / ref->weight ==
((candidate->connections + 1) * 1000) / candidate->weight &&
else if (ref->inv_weight * ref->connections <
candidate->inv_weight * candidate->connections)
{
/* ref has a better score. */
candidate = ref;
}
else if (almost_equal_server_scores(ref->inv_weight * ref->connections,
candidate->inv_weight * candidate->connections) &&
ref->server->stats.n_connections < candidate->server->stats.n_connections)
{
/* This running server has the same number of connections currently as the candidate
but has had fewer connections over time than candidate, set this server to
candidate*/
/* The servers are about equally good, but ref has had fewer connections over time.
* TODO: On second thought, if the servers are currently about equally good,
* should selection not favor the one that has had more connections over time,
* since load balancing has previously found it to be better? Or perhaps
* this check has very little effect anyway.
*/
candidate = ref;
}
}
@ -686,7 +693,7 @@ diagnostics(MXS_ROUTER *router, DCB *dcb)
{
dcb_printf(dcb, "\t\t%-20s %3.1f%% %d\n",
ref->server->name,
(float) ref->weight / 10,
(1.0-ref->inv_weight) * 100,
ref->connections);
}
}
@ -854,8 +861,8 @@ static SERVER_REF *get_root_master(SERVER_REF *servers)
{
if (ref->active && server_is_master(ref->server))
{
// No master found yet or this one has higher weight.
if (master_host == NULL || ref->weight > master_host->weight)
// No master found yet or this one has better weight.
if (master_host == NULL || ref->inv_weight < master_host->inv_weight)
{
master_host = ref;
}