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Remove unnecessary memory allocations

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Given the fact that there exist only three possible categories, the map
can be replaced with a static array that needs no memory
allocations. Making this array thread-local allows it to be reused which
places an upper limit on the number of memory allocations.
This commit is contained in:
Markus Mäkelä
2019-03-05 10:47:56 +02:00
parent e7f739e95d
commit a7be3c527c
1 changed files with 16 additions and 5 deletions
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21
server/modules/routing/readwritesplit/rwsplit_select_backends.cc
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@ -22,6 +22,7 @@
#include <functional>
#include <random>
#include <iostream>
#include <array>
#include <maxbase/stopwatch.hh>
#include <maxscale/router.h>
@ -201,6 +202,11 @@ BackendSelectFunction get_backend_select_function(select_criteria_t sc)
return backend_cmp_current_load;
}
namespace
{
// Buffers for sorting the servers, thread_local to avoid repeated memory allocations
thread_local std::array<SRWBackendVector, 3> priority_map;
}
/**
* @brief Find the best slave candidate for routing reads.
@ -216,7 +222,6 @@ SRWBackendVector::iterator find_best_backend(SRWBackendVector& backends,
bool masters_accepts_reads)
{
// Group backends by priority. The set of highest priority backends will then compete.
std::map<int, SRWBackendVector> priority_map;
int best_priority {INT_MAX}; // low numbers are high priority
for (auto& psBackend : backends)
@ -230,16 +235,16 @@ SRWBackendVector::iterator find_best_backend(SRWBackendVector& backends,
{
if (!is_busy)
{
priority = 1; // highest priority, idle servers
priority = 0; // highest priority, idle servers
}
else
{
priority = 13; // lowest priority, busy servers
priority = 2; // lowest priority, busy servers
}
}
else
{
priority = 2; // idle masters with masters_accept_reads==false
priority = 1; // idle masters with masters_accept_reads==false
}
priority_map[priority].push_back(psBackend);
@ -247,8 +252,14 @@ SRWBackendVector::iterator find_best_backend(SRWBackendVector& backends,
}
auto best = select(priority_map[best_priority]);
auto rval = std::find(backends.begin(), backends.end(), *best);
return std::find(backends.begin(), backends.end(), *best);
for (auto& a : priority_map)
{
a.clear();
}
return rval;
}
/**