Hi,
I noticed a bug in src/test/modules/test_bloomfilter/test_bloomfilter.c
where the false positive rate is displayed incorrectly in
create_and_test_bloom().
The issue is in the ereport() call:
errmsg_internal("seed: " UINT64_FORMAT " false positives: "
INT64_FORMAT " (%.6f%%) bitset %.2f%% set",
seed, nfalsepos, (double) nfalsepos / nelements,
100.0 * bloom_prop_bits_set(filter))
The format specifier %.6f%% expects a value already scaled to a percentage,
but (double) nfalsepos / nelements produces a raw fraction. This means a
true false positive rate of 0.5% is displayed as 0.005000% — 100x smaller
than the actual value.
This is inconsistent with the very next argument, bloom_prop_bits_set(),
which is correctly multiplied by 100.0 before being passed to its %.2f%%
format specifier.
The fix is straightforward — multiply the ratio by 100.0:
- seed, nfalsepos, (double) nfalsepos / nelements,
+ seed, nfalsepos, 100.0 * (double) nfalsepos / nelements,
Patch is attached.
Thanks & Regards,
*Jhon k*
Postgres Specialist
Project & IT Department
Cybrosys Technologies
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From f4ca602e7c902ec34028d0a3a7fded39a9d8669e Mon Sep 17 00:00:00 2001
From: postgress cybrosys <[email protected]>
Date: Wed, 25 Mar 2026 12:17:16 +0530
Subject: [PATCH] Fix incorrect false positive rate formatting in
create_and_test_bloom()
The false positive rate was reported as a raw fraction (e.g., 0.005000%) instead of a percentage (0.500000%). The "%.6f%%" format specifier expects a value already scaled to percentage, but the computed ratio was not multiplied by 100.0.
This is inconsistent with bloom_prop_bits_set(), which correctly scales its value by 100.0 before passing it to a "%.2f%%" format specifier.
Fix by multiplying (nfalsepos / nelements) by 100.0 to ensure correct percentage output.
---
src/test/modules/test_bloomfilter/test_bloomfilter.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/test/modules/test_bloomfilter/test_bloomfilter.c b/src/test/modules/test_bloomfilter/test_bloomfilter.c
index df41066138c..268e1938cad 100644
--- a/src/test/modules/test_bloomfilter/test_bloomfilter.c
+++ b/src/test/modules/test_bloomfilter/test_bloomfilter.c
@@ -94,7 +94,7 @@ create_and_test_bloom(int power, int64 nelements, int callerseed)
ereport((nfalsepos > nelements * FPOSITIVE_THRESHOLD) ? WARNING : DEBUG1,
(errmsg_internal("seed: " UINT64_FORMAT " false positives: " INT64_FORMAT " (%.6f%%) bitset %.2f%% set",
- seed, nfalsepos, (double) nfalsepos / nelements,
+ seed, nfalsepos, 100.0 * (double) nfalsepos / nelements,
100.0 * bloom_prop_bits_set(filter))));
bloom_free(filter);
--
2.34.1
