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Re: xlog location arithmetic

From: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
To: Euler Taveira de Oliveira <euler(at)timbira(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Magnus Hagander <magnus(at)hagander(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: xlog location arithmetic
Date: 2012-02-10 08:32:46
Message-ID: CAHGQGwFW3drMELnwytG5P1Vqk2HBcQbH4M1_jeHLN6L5E2GyNg@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Fri, Feb 10, 2012 at 7:00 AM, Euler Taveira de Oliveira
<euler(at)timbira(dot)com> wrote:
> On 08-02-2012 09:35, Fujii Masao wrote:
>
> Fujii, new patch attached. Thanks for your tests.

Thanks for the new patch!

>> But another problem happened. When I changed pg_proc.h so that the unused
>> OID was assigned to pg_xlog_location_diff(), and executed the above again,
>> I encountered the segmentation fault:
>>
> I reproduced the problems in my old 32-bit laptop. I fixed it casting to
> int64. I also updated the duplicated OID.

Yep, in the updated patch, I could confirm that the function works fine without
any error in my machine. The patch looks fine to me except the following minor
comments:

In the document, it's better to explain clearly that the function subtracts the
second argument from the first.

-    These functions cannot be executed during recovery.
+	These functions cannot be executed during recovery (except
+	<function>pg_xlog_location_diff</function>).

+	<function>pg_xlog_location_diff</> calculates the difference in bytes
+	between two transaction log locations. It can be used with
+	<structname>pg_stat_replication</structname> or some functions shown in
+	<xref linkend="functions-admin-backup-table"> to get the replication lag.

Very minor comment: you should use spaces rather than a tab to indent each line.

>> Why OID needs to be reassigned?
>>
> There isn't a compelling reason. It is just a way to say: "hey, it is another
> function with the same old name".
>
> I'll not attach another version for pg_size_pretty because it is a matter of
> updating a duplicated OID.

Okay, I reviewed the previous patch again. That looks fine to me.

Regards,

-- 
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center

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