Message-ID: <69d9da54-7066-dcc2-5efd-5fdad139bc40@oss.nttdata.com>
Date: Sat, 5 Feb 2022 00:30:26 +0900
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0)
 Gecko/20100101 Thunderbird/91.5.1
Subject: Re: [PATCH] Add min() and max() aggregate functions for xid8
Content-Language: en-US
To: Ken Kato <katouknl@oss.nttdata.com>, pgsql-hackers@lists.postgresql.org
References: <47d77b18c44f87f8222c4c7a3e2dee6b@oss.nttdata.com>
From: Fujii Masao <masao.fujii@oss.nttdata.com>
In-Reply-To: <47d77b18c44f87f8222c4c7a3e2dee6b@oss.nttdata.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Archived-At: <https://www.postgresql.org/message-id/69d9da54-7066-dcc2-5efd-5fdad139bc40%40oss.nttdata.com>
Precedence: bulk


On 2022/02/03 16:45, Ken Kato wrote:
> Hi hackers,
> 
> Unlike xid, xid8 increases monotonically and cannot be reused.
> This trait makes it possible to support min() and max() aggregate functions for xid8.
> I thought they would be useful for monitoring.
> 
> So I made a patch for this.

Thanks for the patch! +1 with this feature.

+	PG_RETURN_FULLTRANSACTIONID((U64FromFullTransactionId(fxid1) > U64FromFullTransactionId(fxid2)) ? fxid1 : fxid2);

Shouldn't we use FullTransactionIdFollows() to compare those two fxid values here, instead?

+	PG_RETURN_FULLTRANSACTIONID((U64FromFullTransactionId(fxid1) < U64FromFullTransactionId(fxid2)) ? fxid1 : fxid2);

Shouldn't we use FullTransactionIdPrecedes() to compare those two fxid values here, instead?

Could you add the regression tests for those min() and max() functions for xid8?

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION