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* [PATCH v8 1/1] pg_lfind32(): add "overlap" code for remaining elements
@ 2024-03-20 19:20 Nathan Bossart <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Nathan Bossart @ 2024-03-20 19:20 UTC (permalink / raw)
---
src/include/port/pg_lfind.h | 109 ++++++++++++++++++++++++------------
1 file changed, 74 insertions(+), 35 deletions(-)
diff --git a/src/include/port/pg_lfind.h b/src/include/port/pg_lfind.h
index b8dfa66eef..f746aabbf9 100644
--- a/src/include/port/pg_lfind.h
+++ b/src/include/port/pg_lfind.h
@@ -80,6 +80,51 @@ pg_lfind8_le(uint8 key, uint8 *base, uint32 nelem)
return false;
}
+#ifndef USE_NO_SIMD
+/*
+ * pg_lfind32_helper
+ *
+ * Searches one 4-register-block of integers. The caller is responsible for
+ * ensuring that there are at least 4-registers-worth of integers remaining.
+ */
+static inline bool
+pg_lfind32_helper(const Vector32 keys, uint32 *base)
+{
+ const uint32 nelem_per_vector = sizeof(Vector32) / sizeof(uint32);
+ Vector32 vals1,
+ vals2,
+ vals3,
+ vals4,
+ result1,
+ result2,
+ result3,
+ result4,
+ tmp1,
+ tmp2,
+ result;
+
+ /* load the next block into 4 registers */
+ vector32_load(&vals1, base);
+ vector32_load(&vals2, &base[nelem_per_vector]);
+ vector32_load(&vals3, &base[nelem_per_vector * 2]);
+ vector32_load(&vals4, &base[nelem_per_vector * 3]);
+
+ /* compare each value to the key */
+ result1 = vector32_eq(keys, vals1);
+ result2 = vector32_eq(keys, vals2);
+ result3 = vector32_eq(keys, vals3);
+ result4 = vector32_eq(keys, vals4);
+
+ /* combine the results into a single variable */
+ tmp1 = vector32_or(result1, result2);
+ tmp2 = vector32_or(result3, result4);
+ result = vector32_or(tmp1, tmp2);
+
+ /* return whether there was a match */
+ return vector32_is_highbit_set(result);
+}
+#endif /* ! USE_NO_SIMD */
+
/*
* pg_lfind32
*
@@ -109,9 +154,9 @@ pg_lfind32(uint32 key, uint32 *base, uint32 nelem)
bool assert_result = false;
/* pre-compute the result for assert checking */
- for (i = 0; i < nelem; i++)
+ for (int j = 0; j < nelem; j++)
{
- if (key == base[i])
+ if (key == base[j])
{
assert_result = true;
break;
@@ -119,46 +164,40 @@ pg_lfind32(uint32 key, uint32 *base, uint32 nelem)
}
#endif
- for (i = 0; i < tail_idx; i += nelem_per_iteration)
+ /*
+ * If there aren't enough elements for the SIMD code, jump to the standard
+ * one-by-one linear search code.
+ */
+ if (nelem <= nelem_per_iteration)
+ goto one_by_one;
+
+ /*
+ * Process as many elements as possible with a block of 4 registers.
+ */
+ do
{
- Vector32 vals1,
- vals2,
- vals3,
- vals4,
- result1,
- result2,
- result3,
- result4,
- tmp1,
- tmp2,
- result;
-
- /* load the next block into 4 registers */
- vector32_load(&vals1, &base[i]);
- vector32_load(&vals2, &base[i + nelem_per_vector]);
- vector32_load(&vals3, &base[i + nelem_per_vector * 2]);
- vector32_load(&vals4, &base[i + nelem_per_vector * 3]);
-
- /* compare each value to the key */
- result1 = vector32_eq(keys, vals1);
- result2 = vector32_eq(keys, vals2);
- result3 = vector32_eq(keys, vals3);
- result4 = vector32_eq(keys, vals4);
-
- /* combine the results into a single variable */
- tmp1 = vector32_or(result1, result2);
- tmp2 = vector32_or(result3, result4);
- result = vector32_or(tmp1, tmp2);
-
- /* see if there was a match */
- if (vector32_is_highbit_set(result))
+ if (pg_lfind32_helper(keys, &base[i]))
{
Assert(assert_result == true);
return true;
}
- }
+
+ i += nelem_per_iteration;
+
+ } while (i < tail_idx);
+
+ /*
+ * Process the last 'nelem_per_iteration' elements in the array with a
+ * 4-register block. This will cause us to check some of the elements
+ * more than once, but that won't affect correctness, and testing has
+ * demonstrated that this helps more cases than it harms.
+ */
+ Assert(assert_result == pg_lfind32_helper(keys, &base[nelem - nelem_per_iteration]));
+ return pg_lfind32_helper(keys, &base[nelem - nelem_per_iteration]);
+
#endif /* ! USE_NO_SIMD */
+one_by_one:
/* Process the remaining elements one at a time. */
for (; i < nelem; i++)
{
--
2.25.1
--xHFwDpU9dbj6ez1V--
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: [PATCH] Add max_logical_replication_slots GUC
@ 2026-01-29 13:21 Euler Taveira <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Euler Taveira @ 2026-01-29 13:21 UTC (permalink / raw)
To: Ahmed Et-tanany <[email protected]>; Fujii Masao <[email protected]>; +Cc: Álvaro Herrera <[email protected]>; [email protected]
On Thu, Jan 29, 2026, at 10:01 AM, Ahmed Et-tanany wrote:
>
> That's a great point! I'm thinking we could potentially avoid
> introducing a separate max_logical_wal_senders GUC by reusing
> max_logical_replication_slots to decide whether a WAL sender can
> start for logical replication.
>
> This way, the limit on logical slots would also indirectly cap
> the number of logical WAL senders, helping protect physical
> replication connections without adding another configuration
> parameter.
>
You have 2 resources (walsender and replication slot). You are restricting a
resource based on a configuration from another resource. That seems a potential
source of confusion.
--
Euler Taveira
EDB https://www.enterprisedb.com/
^ permalink raw reply [nested|flat] 2+ messages in thread
end of thread, other threads:[~2026-01-29 13:21 UTC | newest]
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2024-03-20 19:20 [PATCH v8 1/1] pg_lfind32(): add "overlap" code for remaining elements Nathan Bossart <[email protected]>
2026-01-29 13:21 Re: [PATCH] Add max_logical_replication_slots GUC Euler Taveira <[email protected]>
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