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PFSELFTEST improved to test the approximation error.

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This commit is contained in:
antirez 2014-04-03 10:17:39 +02:00
parent cf34507b87
commit be9860d0e9
1 changed files with 35 additions and 6 deletions
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41
src/hyperloglog.c
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@ -628,18 +628,17 @@ void pfmergeCommand(redisClient *c) {
}
/* This command performs a self-test of the HLL registers implementation.
* Something that is not easy to test from within the outside.
*
* The test is conceived to test that the different counters of our data
* structure are accessible and that setting their values both result in
* the correct value to be retained and not affect adjacent values. */
* Something that is not easy to test from within the outside. */
#define REDIS_HLL_TEST_CYCLES 1000
void pfselftestCommand(redisClient *c) {
int j, i;
sds bitcounters = sdsnewlen(NULL,REDIS_HLL_SIZE);
uint8_t bytecounters[REDIS_HLL_REGISTERS];
/* Test 1: access registers.
* The test is conceived to test that the different counters of our data
* structure are accessible and that setting their values both result in
* the correct value to be retained and not affect adjacent values. */
for (j = 0; j < REDIS_HLL_TEST_CYCLES; j++) {
/* Set the HLL counters and an array of unsigned byes of the
* same size to the same set of random values. */
@ -663,6 +662,36 @@ void pfselftestCommand(redisClient *c) {
}
}
/* Test 2: approximation error.
* The test is adds unique elements and check that the estimated value
* is always reasonable bounds.
*
* We check that the error is smaller than 4 times than the expected
* standard error, to make it very unlikely for the test to fail because
* of a "bad" run. */
memset(bitcounters,0,REDIS_HLL_SIZE);
double relerr = 1.04/sqrt(REDIS_HLL_REGISTERS);
int64_t checkpoint = 1000;
uint64_t seed = (uint64_t)rand() | (uint64_t)rand() << 32;
uint64_t ele;
for (j = 1; j <= 10000000; j++) {
ele = j ^ seed;
hllAdd((uint8_t*)bitcounters,(unsigned char*)&ele,sizeof(ele));
if (j == checkpoint) {
int64_t abserr = checkpoint-
(int64_t)hllCount((uint8_t*)bitcounters);
if (abserr < 0) abserr = -abserr;
if (abserr > (uint64_t)(relerr*4*checkpoint)) {
addReplyErrorFormat(c,
"TESTFAILED Too big error. card:%llu abserr:%llu",
(unsigned long long) checkpoint,
(unsigned long long) abserr);
goto cleanup;
}
checkpoint *= 10;
}
}
/* Success! */
addReply(c,shared.ok);