mirror of https://github.com/yandex/odyssey.git
94 lines
2.1 KiB
C
94 lines
2.1 KiB
C
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/*
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* Odyssey.
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*
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* Scalable PostgreSQL connection pooler.
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*
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* Implementation of reservoir sampling algorithm
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*/
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#include <stdlib.h>
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#include <stdarg.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <string.h>
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#include <ctype.h>
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#include <inttypes.h>
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#include <assert.h>
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#include <machinarium.h>
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#include <kiwi.h>
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#include <odyssey.h>
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void
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od_hgram_init(od_hgram_t *hgram)
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{
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memset(hgram, 0, sizeof(*hgram));
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}
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// Probablisticaly add data point, return 1 is point was actually added to data
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// set, 0 otherwise
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int
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od_hgram_add_data_point(od_hgram_t *hgram, uint64_t point)
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{
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uint64_t next_position = __sync_fetch_and_add(&hgram->estimated_size, 1);
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if (next_position < OD_HGRAM_DATA_POINTS) {
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hgram->data[next_position] = point;
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return 1;
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}
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next_position = machine_lrand48() % next_position;
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if (next_position < OD_HGRAM_DATA_POINTS) {
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hgram->data[next_position] = point;
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return 1;
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}
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return 0;
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}
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static int
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cmpfunc_ui32(const void *a, const void *b)
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{
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if (*(uint32_t *)a < *(uint32_t *)b)
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return 1;
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if (*(uint32_t *)a > *(uint32_t *)b)
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return -1;
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return 0;
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}
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// Create static copy of reservoir for analysis
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void
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od_hgram_freeze(od_hgram_t *hgram,
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od_hgram_frozen_t *hgram_tmp,
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od_hgram_freeze_type_t type)
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{
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if (hgram == NULL) {
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hgram_tmp->estimated_size = 0;
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return;
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}
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memcpy(hgram_tmp, hgram, sizeof(*hgram));
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if (type == OD_HGRAM_FREEZ_RESET) {
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hgram->estimated_size = 0;
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} else if (type == OD_HGRAM_FREEZ_REDUCE &&
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hgram_tmp->estimated_size > OD_HGRAM_DATA_POINTS) {
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hgram->estimated_size = OD_HGRAM_DATA_POINTS;
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}
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qsort(
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&hgram_tmp->data, OD_HGRAM_DATA_POINTS, sizeof(uint32_t), cmpfunc_ui32);
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if (hgram_tmp->estimated_size > OD_HGRAM_DATA_POINTS) {
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hgram_tmp->estimated_size = OD_HGRAM_DATA_POINTS;
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}
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}
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// Compute quantile withing static copy of reservoir
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uint64_t
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od_hgram_quantile(od_hgram_frozen_t *frozen, double quantile)
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{
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assert(quantile > 0);
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assert(quantile <= 1);
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if (frozen->estimated_size == 0)
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return 0;
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return frozen->data[(size_t)(frozen->estimated_size * (1 - quantile))];
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}
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