Message-ID: <98229784-1ce8-4100-9236-a77f635f596b@vondra.me>
Date: Mon, 23 Sep 2024 12:26:40 +0200
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Subject: Re: scalability bottlenecks with (many) partitions (and more)
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jakub Wartak <jakub.wartak@enterprisedb.com>,
 Robert Haas <robertmhaas@gmail.com>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Andres Freund <andres@anarazel.de>
References: <510b887e-c0ce-4a0c-a17a-2c6abb8d9a5c@enterprisedb.com>
 <52afd566-d110-43ea-ae72-69349d4414f6@vondra.me>
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 <CA+TgmoZ-40G7-WoLSsEH+7FqUzrP_0ndCOkewJ7ifAO6MVx0EA@mail.gmail.com>
 <b8c43eda-0c3f-4cb4-809b-841fa5c40ada@vondra.me>
 <CA+TgmobCBse3LYj9pfh-ELbP0VnffQS7jP_vNTGA7-KZP0gqDw@mail.gmail.com>
 <52f026c4-6c4e-4de2-bd78-609091d7c772@vondra.me>
 <CA+TgmoamAOj5e4J7WcC9g10AskvVPk5D7JoAvWw8DFnpHMiSQA@mail.gmail.com>
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 <0775ba8a-920c-4d37-b202-989a90b6ee4c@vondra.me>
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 <2891628.1727019959@sss.pgh.pa! .us>
 <5a5be673-4102-4c52-b504-1b205d5b7f83@vondra.me>
 <2942266.1727046406@sss.pgh.pa.us>
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From: Tomas Vondra <tomas@vondra.me>
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On 9/23/24 01:06, Tom Lane wrote:
> Tomas Vondra <tomas@vondra.me> writes:
>> On 9/22/24 17:45, Tom Lane wrote:
>>> #define FAST_PATH_GROUP(index)	\
>>> -	(AssertMacro(((index) >= 0) && ((index) < FP_LOCK_SLOTS_PER_BACKEND)), \
>>> +	(AssertMacro((uint32) (index) < FP_LOCK_SLOTS_PER_BACKEND), \
>>> ((index) / FP_LOCK_SLOTS_PER_GROUP))
> 
>> For the (x >= 0) asserts, doing it this way relies on negative values
>> wrapping to large positive ones, correct? AFAIK it's guaranteed to be a
>> very large value, so it can't accidentally be less than the slot count.
> 
> Right, any negative value would wrap to something more than
> INT32_MAX.
> 

Thanks. Pushed a fix for these issues, hopefully coverity will be happy.

BTW is the coverity report accessible somewhere? I know someone
mentioned that in the past, but I don't recall the details. Maybe we
should have a list of all these resources, useful for committers,
somewhere on the wiki?


regards

-- 
Tomas Vondra