Line data    Source code

       1             : /*--------------------------------------------------------------------------
       2             :  *
       3             :  * test_bloomfilter.c
       4             :  *      Test false positive rate of Bloom filter.
       5             :  *
       6             :  * Copyright (c) 2018-2024, PostgreSQL Global Development Group
       7             :  *
       8             :  * IDENTIFICATION
       9             :  *      src/test/modules/test_bloomfilter/test_bloomfilter.c
      10             :  *
      11             :  * -------------------------------------------------------------------------
      12             :  */
      13             : #include "postgres.h"
      14             : 
      15             : #include "common/pg_prng.h"
      16             : #include "fmgr.h"
      17             : #include "lib/bloomfilter.h"
      18             : #include "miscadmin.h"
      19             : 
      20           2 : PG_MODULE_MAGIC;
      21             : 
      22             : /* Fits decimal representation of PG_INT64_MIN + 2 bytes: */
      23             : #define MAX_ELEMENT_BYTES       21
      24             : /* False positive rate WARNING threshold (1%): */
      25             : #define FPOSITIVE_THRESHOLD     0.01
      26             : 
      27             : 
      28             : /*
      29             :  * Populate an empty Bloom filter with "nelements" dummy strings.
      30             :  */
      31             : static void
      32           2 : populate_with_dummy_strings(bloom_filter *filter, int64 nelements)
      33             : {
      34             :     char        element[MAX_ELEMENT_BYTES];
      35             :     int64       i;
      36             : 
      37     1677724 :     for (i = 0; i < nelements; i++)
      38             :     {
      39     1677722 :         CHECK_FOR_INTERRUPTS();
      40             : 
      41     1677722 :         snprintf(element, sizeof(element), "i" INT64_FORMAT, i);
      42     1677722 :         bloom_add_element(filter, (unsigned char *) element, strlen(element));
      43             :     }
      44           2 : }
      45             : 
      46             : /*
      47             :  * Returns number of strings that are indicated as probably appearing in Bloom
      48             :  * filter that were in fact never added by populate_with_dummy_strings().
      49             :  * These are false positives.
      50             :  */
      51             : static int64
      52           2 : nfalsepos_for_missing_strings(bloom_filter *filter, int64 nelements)
      53             : {
      54             :     char        element[MAX_ELEMENT_BYTES];
      55           2 :     int64       nfalsepos = 0;
      56             :     int64       i;
      57             : 
      58     1677724 :     for (i = 0; i < nelements; i++)
      59             :     {
      60     1677722 :         CHECK_FOR_INTERRUPTS();
      61             : 
      62     1677722 :         snprintf(element, sizeof(element), "M" INT64_FORMAT, i);
      63     1677722 :         if (!bloom_lacks_element(filter, (unsigned char *) element,
      64             :                                  strlen(element)))
      65       13568 :             nfalsepos++;
      66             :     }
      67             : 
      68           2 :     return nfalsepos;
      69             : }
      70             : 
      71             : static void
      72           2 : create_and_test_bloom(int power, int64 nelements, int callerseed)
      73             : {
      74             :     int         bloom_work_mem;
      75             :     uint64      seed;
      76             :     int64       nfalsepos;
      77             :     bloom_filter *filter;
      78             : 
      79           2 :     bloom_work_mem = (1L << power) / 8L / 1024L;
      80             : 
      81           2 :     elog(DEBUG1, "bloom_work_mem (KB): %d", bloom_work_mem);
      82             : 
      83             :     /*
      84             :      * Generate random seed, or use caller's.  Seed should always be a
      85             :      * positive value less than or equal to PG_INT32_MAX, to ensure that any
      86             :      * random seed can be recreated through callerseed if the need arises.
      87             :      */
      88           2 :     seed = callerseed < 0 ? pg_prng_int32p(&pg_global_prng_state) : callerseed;
      89             : 
      90             :     /* Create Bloom filter, populate it, and report on false positive rate */
      91           2 :     filter = bloom_create(nelements, bloom_work_mem, seed);
      92           2 :     populate_with_dummy_strings(filter, nelements);
      93           2 :     nfalsepos = nfalsepos_for_missing_strings(filter, nelements);
      94             : 
      95           2 :     ereport((nfalsepos > nelements * FPOSITIVE_THRESHOLD) ? WARNING : DEBUG1,
      96             :             (errmsg_internal("seed: " UINT64_FORMAT " false positives: " INT64_FORMAT " (%.6f%%) bitset %.2f%% set",
      97             :                              seed, nfalsepos, (double) nfalsepos / nelements,
      98             :                              100.0 * bloom_prop_bits_set(filter))));
      99             : 
     100           2 :     bloom_free(filter);
     101           2 : }
     102             : 
     103           4 : PG_FUNCTION_INFO_V1(test_bloomfilter);
     104             : 
     105             : /*
     106             :  * SQL-callable entry point to perform all tests.
     107             :  *
     108             :  * If a 1% false positive threshold is not met, emits WARNINGs.
     109             :  *
     110             :  * See README for details of arguments.
     111             :  */
     112             : Datum
     113           2 : test_bloomfilter(PG_FUNCTION_ARGS)
     114             : {
     115           2 :     int         power = PG_GETARG_INT32(0);
     116           2 :     int64       nelements = PG_GETARG_INT64(1);
     117           2 :     int         seed = PG_GETARG_INT32(2);
     118           2 :     int         tests = PG_GETARG_INT32(3);
     119             :     int         i;
     120             : 
     121           2 :     if (power < 23 || power > 32)
     122           0 :         elog(ERROR, "power argument must be between 23 and 32 inclusive");
     123             : 
     124           2 :     if (tests <= 0)
     125           0 :         elog(ERROR, "invalid number of tests: %d", tests);
     126             : 
     127           2 :     if (nelements < 0)
     128           0 :         elog(ERROR, "invalid number of elements: %d", tests);
     129             : 
     130           4 :     for (i = 0; i < tests; i++)
     131             :     {
     132           2 :         elog(DEBUG1, "beginning test #%d...", i + 1);
     133             : 
     134           2 :         create_and_test_bloom(power, nelements, seed);
     135             :     }
     136             : 
     137           2 :     PG_RETURN_VOID();
     138             : }