Re: Fix overflow of nbatch
| От | Chao Li |
|---|---|
| Тема | Re: Fix overflow of nbatch |
| Дата | |
| Msg-id | EB65FD9A-5A32-4841-A2FC-09F39D6C8532@gmail.com обсуждение исходный текст |
| Ответ на | Fix overflow of nbatch (Vaibhav Jain <jainva@google.com>) |
| Ответы |
Re: Fix overflow of nbatch
|
| Список | pgsql-hackers |
On Sep 22, 2025, at 21:20, Vaibhav Jain <jainva@google.com> wrote:Hi Everyone,<0001-Fix-overflow-of-nbatch.patch>With a1b4f28, to compute current_space, nbatch is being multiplied
by BLCKSZ. nbatch is int and when multiplied with BLCKSZ, it can
easily overflow the int limit.To keep the calculation safe for
current_space, convert nbatch to size_t.Please find a patch for the same.Thanks,Vaibhav
I guess that because earlier in the function, nbatch is always clamped with:
nbatch = pg_nextpower2_32(Max(2, minbatch));So, in practice, nbatch won’t grow to very big. But yes, if nbatch reaches to, say 1 million, it will overflow.
A simple program proves that changing nbatch to size_t will prevent from overflowing:
```
#include <stdio.h>
int main(){
size_t nbatch = 1000000; // 1 million
int BLCKSZ = 8192;
size_t result = 2 * nbatch * BLCKSZ;
printf("%zu\n", result); // will output 16384000000
return 0;
}
```
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
HighGo Software Co., Ltd.
https://www.highgo.com/
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