Subject: Added documentation about caching, reliability

From: Bruce Momjian <[email-masked]>
Date: Wed, 28 Sep 2005 14:26:24 -0400 (EDT)

I have added a section to the top of the WAL docs explaining caching and
reliability issues:

	http://candle.pha.pa.us/main/writings/pgsql/sgml/reliability.html

I also renamed the chapter "Reilability" rather than "WAL."

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  [email-masked]               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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From: "Jonah H. Harris" <[email-masked]>
Date: Wed, 28 Sep 2005 14:37:34 -0400

Hey Bruce,

One grammar issue... otherwise great work.

they can be moved to another computer with similar hardware and all
committed transaction will remain intact.

should be

they can be moved to another computer with similar hardware and all
committed transactions will remain intact.

On 9/28/05, Bruce Momjian <[email-masked]> wrote:
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--
Respectfully,

Jonah H. Harris, Database Internals Architect
EnterpriseDB Corporation
http://www.enterprisedb.com/

---

From: Bruce Momjian <[email-masked]>
Date: Wed, 28 Sep 2005 14:40:37 -0400 (EDT)

Thanks, fixed.

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From: Alvaro Herrera <[email-masked]>
Date: Wed, 28 Sep 2005 15:49:34 -0400

> I also renamed the chapter "Reilability" rather than "WAL."

While you are re-titling the docs, maybe the sections on that chapter
could be titled "Benefits of Write-Ahead Log" instead of "Benefits of
WAL", etc.

-- 
Alvaro Herrera                  http://www.amazon.com/gp/registry/DXLWNGRJD34
"La realidad se compone de muchos sueños, todos ellos diferentes,
pero en cierto aspecto, parecidos..." (Yo, hablando de sueños eróticos)

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From: Bruce Momjian <[email-masked]>
Date: Wed, 28 Sep 2005 22:08:02 -0400 (EDT)

> could be titled "Benefits of Write-Ahead Log" instead of "Benefits of

The chapter sections are:

	Table of Contents
	26.1. Write-Ahead Logging (WAL)
	26.2. Benefits of WAL
	26.3. WAL Configuration
	26.4. WAL Internals

Are you suggesting we spell out Write-Ahead Logging for all section
titles?

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From: "Jonah H. Harris" <[email-masked]>
Date: Wed, 28 Sep 2005 20:16:06 -0600

IMHO, spelling out each one is redundant... the first one "Write-Ahead
Logging (WAL)" seems to define WAL for use later in the text.

--
Respectfully,

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From: Alvaro Herrera <[email-masked]>
Date: Wed, 28 Sep 2005 22:23:49 -0400

> Are you suggesting we spell out Write-Ahead Logging for all section

Is it considered good style to use acronyms in titles?  I wouldn't do it.

Maybe it could be left as

 	26.1. Write-Ahead Logging
 	26.2. Benefits of Write-Ahead Logging
 	26.3. WAL Configuration
 	26.4. WAL Internals

because the former two talk about WAL in a general manner, while the
latter two are about our implementation.  I also wouldn't expand the
acronym in a title.

-- 
Alvaro Herrera       Valdivia, Chile   ICBM: S 39º 49' 17.7", W 73º 14' 26.8"
Thou shalt study thy libraries and strive not to reinvent them without
cause, that thy code may be short and readable and thy days pleasant
and productive. (7th Commandment for C Programmers)

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From: Bruce Momjian <[email-masked]>
Date: Wed, 28 Sep 2005 22:30:40 -0400 (EDT)

>  	26.2. Benefits of Write-Ahead Logging

I modified 26.2 as you suggested.

> latter two are about our implementation.  I also wouldn't expand the

I think we do need to show the acronym in the title if use that acronym
in later titles.

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From: Peter Eisentraut <[email-masked]>
Date: Thu, 29 Sep 2005 08:38:47 +0200

> I also renamed the chapter "Reilability" rather than "WAL."

Considering that the chapter is, in fact, all about WAL, I don't think this is 
a good move.  Reliability is a concern that is not only addressed by the WAL 
system.  Please change it back.

-- 
Peter Eisentraut
http://developer.postgresql.org/~petere/

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From: Bruce Momjian <[email-masked]>
Date: Thu, 29 Sep 2005 10:40:51 -0400 (EDT)

> system.  Please change it back.

Well, now the chapter is about WAL and reliability, so I thought
reliability hit both topics.  Also, maybe we should consider moving this
FAQ item into the docs:

    <H3><A name="3.7">3.7</A>) What computer hardware should I use?</H3>

    <P>Because PC hardware is mostly compatible, people tend to believe that
    all PC hardware is of equal quality.  It is not.  ECC RAM, SCSI, and
    quality motherboards are more reliable and have better performance than
    less expensive hardware.  PostgreSQL will run on almost any hardware,
    but if reliability and performance are important it is wise to
    research your hardware options thoroughly.  Our email lists can be used
    to discuss hardware options and tradeoffs.</P>

Anyway, I thought the previous chapter title, WAL, was weird because it
was hard to know why an administrator would care about WAL --- there was
no lead-in to the term.  This way, it is all under reliability, and can
add to it.

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From: Peter Eisentraut <[email-masked]>
Date: Thu, 29 Sep 2005 17:13:24 +0200

Bruce Momjian wrote:
> reliability hit both topics. Also, maybe we should consider moving 
> this FAQ item into the docs:
>

Hardware choice and configuration are important topics, but neither of 
these are strongly tied to either WAL or Reliability.  Reliability is 
the property (not a "feature") of a system to do what you meant for it 
to do.  Certainly WAL contributes to that by increasing tolerance 
against hardware failures, but it still seems to be a rather 
far-fetched connection to pair these two.

I could see hardware issues being discussed in chapter 16, since we 
already have operating system and kernel configuration there, and it's 
the chapter a user will read when setting up a server system.

I was never all that happy with the WAL chapter, since, as you say, it 
doesn't seem to be a first-class user-level feature.  I'd be happy to 
integrate it into another chapter, but I'm not sure where.

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From: Bruce Momjian <[email-masked]>
Date: Thu, 29 Sep 2005 11:17:00 -0400 (EDT)

> integrate it into another chapter, but I'm not sure where.

Sure, I am looking for suggestions.  My relabeling at least fixes that,
but feel free to move things around and relabel them.

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From: Simon Riggs <[email-masked]>
Date: Sun, 09 Oct 2005 09:54:42 +0100

> I also renamed the chapter "Reilability" rather than "WAL."

I submitted a patch last week that builds further on Bruce's changes.
[Docs for PITR and full_page_writes interaction, 2 Oct]

The patch includes:

1. Minor rewording of the case that Bruce refers to "recovery" and I
have differentiated the cases of crash recovery and PITR. The
corresponding section of the backup chapter has also been changed to
include a short discussion on full_page_writes and WAL compression, with
a link back to the WAL section.

2. Merged the 1st and 2nd sects of Reliability into a single section.
The 1st section was only a single paragraph and so that improves
readability. I've freshened that section, since it has not been updated
since 7.1 and currently still reads as if WAL has just been released.

3. I've updated the section on WAL configuration with further WAL
related comments and clarifications. These relate to full_page_writes
and appropriate settings of wal_buffers to match.

Best Regards, Simon Riggs

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From: Bruce Momjian <[email-masked]>
Date: Thu, 13 Oct 2005 13:33:16 -0400 (EDT)

Applied.  Thanks.

Simon Riggs wrote:
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