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* BUG #19634: Hash partition with large MODULUS causes "invalid memory alloc request size"
@ 2026-08-21 03:44 PG Bug reporting form <noreply@postgresql.org>
2026-08-21 12:04 ` Re: BUG #19634: Hash partition with large MODULUS causes "invalid memory alloc request size" Pierre Forstmann <pierre.forstmann@gmail.com>
0 siblings, 1 reply; 3+ messages in thread
From: PG Bug reporting form @ 2026-08-21 03:44 UTC (permalink / raw)
To: pgsql-bugs@lists.postgresql.org; +Cc: hackerzheng666@gmail.com
The following bug has been logged on the website:
Bug reference: 19634
Logged by: Zheng Hacker
Email address: hackerzheng666@gmail.com
PostgreSQL version: 19beta3
Operating system: Linux x86_64
Description:
Creating a hash partition with MODULUS >= 268435457 causes an internal error
"invalid memory alloc request size" on any subsequent query against the
partitioned table. The table becomes permanently unusable — SELECT,
INSERT,
and all other operations fail with the same error. Only DROP TABLE works.
Minimal reproducer (tested on PG 20devel commit 609f969, 2026-08-21):
CREATE TABLE t (id int) PARTITION BY HASH (id);
CREATE TABLE t_p0 PARTITION OF t FOR VALUES WITH (MODULUS 268435457,
REMAINDER 0);
SELECT * FROM t; -- ERROR: invalid memory alloc request size 1073741828
Root cause:
In src/backend/partitioning/partbounds.c, create_hash_bounds() (line 390)
allocates an array indexed by greatest_modulus:
boundinfo->nindexes = greatest_modulus;
boundinfo->indexes = palloc_array(int, greatest_modulus);
When greatest_modulus >= 268435457, this requests 268435457 * 4 =
1073741828
bytes, exceeding MaxAllocSize (1073741823 = 1GB - 1). No bounds check
exists
on the modulus value before this allocation.
The validation in check_new_partition_bound() (line ~2927) runs AFTER
create_hash_bounds() is called during partition descriptor loading, so it
never gets a chance to reject the invalid modulus.
Impact:
- Affects all versions since hash partitioning was introduced (PG 11+)
- The partition is created successfully (CREATE TABLE succeeds)
- But any access to the parent table fails permanently
- Only DROP TABLE recovers the table
- Any unprivileged user with CREATE TABLE permission can trigger this
Suggested fix:
Add a bounds check in create_hash_bounds() before the allocation, or
validate modulus against MaxAllocSize in check_new_partition_bound()
before partition descriptor loading.
PostgreSQL version: 20devel (commit 609f969)
OS: Ubuntu 22.04 x86_64
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: BUG #19634: Hash partition with large MODULUS causes "invalid memory alloc request size"
2026-08-21 03:44 BUG #19634: Hash partition with large MODULUS causes "invalid memory alloc request size" PG Bug reporting form <noreply@postgresql.org>
@ 2026-08-21 12:04 ` Pierre Forstmann <pierre.forstmann@gmail.com>
2026-08-21 12:24 ` Re: BUG #19634: Hash partition with large MODULUS causes "invalid memory alloc request size" Andres Freund <andres@anarazel.de>
0 siblings, 1 reply; 3+ messages in thread
From: Pierre Forstmann @ 2026-08-21 12:04 UTC (permalink / raw)
To: pgsql-bugs@lists.postgresql.org; +Cc: hackerzheng666@gmail.com
Hello,
I propose following patch that adds the check to new_partition_bound
routine:
postgres=# CREATE TABLE t (id int) PARTITION BY HASH (id);
CREATE TABLE
postgres=# CREATE TABLE t_p0 PARTITION OF t FOR VALUES WITH (MODULUS
268435457,
REMAINDER 0);
ERROR: hash partitions bounds are too large
DETAIL: Creating hash partitions for modulus 268435457 would require
too much memory.
HINT: Reduce the number of partitions.
postgres=#
Regards,
Pierre Forstmann
Le 21/08/2026 à 05:44, PG Bug reporting form a écrit :
> The following bug has been logged on the website:
>
> Bug reference: 19634
> Logged by: Zheng Hacker
> Email address: hackerzheng666@gmail.com
> PostgreSQL version: 19beta3
> Operating system: Linux x86_64
> Description:
>
> Creating a hash partition with MODULUS >= 268435457 causes an internal error
> "invalid memory alloc request size" on any subsequent query against the
> partitioned table. The table becomes permanently unusable — SELECT,
> INSERT,
> and all other operations fail with the same error. Only DROP TABLE works.
>
> Minimal reproducer (tested on PG 20devel commit 609f969, 2026-08-21):
>
> CREATE TABLE t (id int) PARTITION BY HASH (id);
> CREATE TABLE t_p0 PARTITION OF t FOR VALUES WITH (MODULUS 268435457,
> REMAINDER 0);
> SELECT * FROM t; -- ERROR: invalid memory alloc request size 1073741828
>
> Root cause:
> In src/backend/partitioning/partbounds.c, create_hash_bounds() (line 390)
> allocates an array indexed by greatest_modulus:
>
> boundinfo->nindexes = greatest_modulus;
> boundinfo->indexes = palloc_array(int, greatest_modulus);
>
> When greatest_modulus >= 268435457, this requests 268435457 * 4 =
> 1073741828
> bytes, exceeding MaxAllocSize (1073741823 = 1GB - 1). No bounds check
> exists
> on the modulus value before this allocation.
>
> The validation in check_new_partition_bound() (line ~2927) runs AFTER
> create_hash_bounds() is called during partition descriptor loading, so it
> never gets a chance to reject the invalid modulus.
>
> Impact:
> - Affects all versions since hash partitioning was introduced (PG 11+)
> - The partition is created successfully (CREATE TABLE succeeds)
> - But any access to the parent table fails permanently
> - Only DROP TABLE recovers the table
> - Any unprivileged user with CREATE TABLE permission can trigger this
>
> Suggested fix:
> Add a bounds check in create_hash_bounds() before the allocation, or
> validate modulus against MaxAllocSize in check_new_partition_bound()
> before partition descriptor loading.
>
> PostgreSQL version: 20devel (commit 609f969)
> OS: Ubuntu 22.04 x86_64
>
>
>
>
Attachments:
[text/x-patch] 0001-v1-0001-Fix-memory-allocation-check.patch (1.6K, ../../19d59133-7a9b-4d9f-a439-201d143bdb5f@gmail.com/2-0001-v1-0001-Fix-memory-allocation-check.patch)
download | inline diff:
From 7ca80f33b806e2b322e9631e01046173b276e87e Mon Sep 17 00:00:00 2001
From: Pierre Forstmann <pierre.forstmann@gmail.com>
Date: Fri, 21 Aug 2026 13:56:29 +0200
Subject: [PATCH] v1-0001-Fix-memory-allocation-check
---
src/backend/partitioning/partbounds.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/src/backend/partitioning/partbounds.c b/src/backend/partitioning/partbounds.c
index 865a92c8561..15ab0f715d4 100644
--- a/src/backend/partitioning/partbounds.c
+++ b/src/backend/partitioning/partbounds.c
@@ -2918,6 +2918,14 @@ check_new_partition_bound(char *relname, Relation parent,
Assert(spec->strategy == PARTITION_STRATEGY_HASH);
Assert(spec->remainder >= 0 && spec->remainder < spec->modulus);
+ /* Check needed memory that will be allocated in create_hash_bounds() */
+ if (spec->modulus * sizeof(int) > MaxAllocSize)
+ ereport(ERROR, (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+ (errmsg("hash partitions bounds are too large"),
+ errdetail("Creating hash partitions for modulus %d would require too much memory.", spec->modulus),
+ errhint("Reduce the number of partitions."))));
+
+
if (partdesc->nparts > 0)
{
int greatest_modulus;
@@ -3030,8 +3038,10 @@ check_new_partition_bound(char *relname, Relation parent,
}
remainder += spec->modulus;
} while (remainder < greatest_modulus);
+
}
+
break;
}
--
2.47.3
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: BUG #19634: Hash partition with large MODULUS causes "invalid memory alloc request size"
2026-08-21 03:44 BUG #19634: Hash partition with large MODULUS causes "invalid memory alloc request size" PG Bug reporting form <noreply@postgresql.org>
2026-08-21 12:04 ` Re: BUG #19634: Hash partition with large MODULUS causes "invalid memory alloc request size" Pierre Forstmann <pierre.forstmann@gmail.com>
@ 2026-08-21 12:24 ` Andres Freund <andres@anarazel.de>
0 siblings, 0 replies; 3+ messages in thread
From: Andres Freund @ 2026-08-21 12:24 UTC (permalink / raw)
To: Pierre Forstmann <pierre.forstmann@gmail.com>; +Cc: pgsql-bugs@lists.postgresql.org; hackerzheng666@gmail.com
Hi,
On 2026-08-21 14:04:09 +0200, Pierre Forstmann wrote:
> I propose following patch that adds the check to new_partition_bound
> routine:
>
> postgres=# CREATE TABLE t (id int) PARTITION BY HASH (id);
> CREATE TABLE
> postgres=# CREATE TABLE t_p0 PARTITION OF t FOR VALUES WITH (MODULUS
> 268435457,
> REMAINDER 0);
> ERROR: hash partitions bounds are too large
> DETAIL: Creating hash partitions for modulus 268435457 would require too
> much memory.
> HINT: Reduce the number of partitions.
> postgres=#
I am not sure it's worth doing *anything* here. There's at most a slightly
suboptimal error message here. There are many many ways to get those. Nobody
sane would create a setup like this unless they're explicitly trying to find
unexpected errors or such.
Greetings,
Andres Freund
^ permalink raw reply [nested|flat] 3+ messages in thread
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2026-08-21 03:44 BUG #19634: Hash partition with large MODULUS causes "invalid memory alloc request size" PG Bug reporting form <noreply@postgresql.org>
2026-08-21 12:04 ` Pierre Forstmann <pierre.forstmann@gmail.com>
2026-08-21 12:24 ` Andres Freund <andres@anarazel.de>
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