Tag Archives: postgres

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FSM, visibility map and new VACUUM awesomeness


Heikki Linnakangas, listening as Simon Riggs sketches on the chalkboard.

Update: Heikki’s slides are here!

Heikki Linnakangas gave a presentation this past Sunday at FOSDEM about the improved free space map (FSM), which tracks unused space inside the database, and new visibility map, a bitmap which will indicate which data pages can be skipped during a partial VACUUM. This performance enhancement will affect all users of the upcoming 8.4 software release. You can see what the new FSM implementation looked like back in October from depesz’s blog.

Despite Heikki’s modest claim during the talk that the performance tests were inconclusive, the consensus among Postgres contributors is that this feature will result a substantial improvement in the performance of VACUUM for tables that are large, but have few UPDATEs.

The new free space map and Visibility map (in 8.4) and autovacuum (enabled by default starting in version 8.2) are huge administrative usability improvements to version 8 of Postgres. Prior to version 8.1, VACUUM had to be scheduled outside of database system. Autovacuum has been part of the core Postgres distribution for over two years, and is tunable via several global configuration parameters.

The visibility map enables partial VACUUMs — meaning that VACUUM no longer has to examine every tuple to update the FSM. The new FSM implementation eliminates two configuration parameters, effectively automating a formerly manual configuration process.

The new FSM is stored on disk in seperate files inside of $PGDATA/base/, and is cached in shared_buffers. The result is that the max_fsm_* configuration parameters are no longer in 8.4 — Postgres is able to track and adjust this data structure without user intervention.

A few critical features of the new FSM are:

* Now a binary tree structure
* Constructed using 1 byte per heap page
* The top level shows the maximum amount of contiguous space available
* The data structure is auto-repairing and can be reconstructed from the bottom

Previously, every time that VACUUM was run, the free space map had to be reconstructed from scratch. Now, individual nodes in the map may be updated (aka “retail” updates).

Visibility map is a bitmap of heap pages which tracks which tuples on pages are visible to transactions, and therefore not available for VACUUMing.

Previously, when VACUUM ran, it *had* to look at every tuple in a table, because there was no information about which pages may not have been updated since the last VACUUM. With the visibility map, VACUUM will now be able to perform partial scans of table data, skipping pages which are marked as fully visible. Partial scans means fewer I/O operations for VACUUM, and happier database administrators.

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Leading without being in charge: updated slides for FOSDEM 2009

I’ve got a post about Heikki’s visibility map talk in the queue, but first I’ll post the updated slides for the user groups talk — Leading without being in charge.

Enjoy!

Leading Without Being In Charge

View more presentations from Selena Deckelmann. (tags: user groups)

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Simon Riggs just rocked my world.

I’m in Brussels for the FOSDEM conference, hanging out at the PostgreSQL booth, meeting my European colleagues, and running into friends.

PostgreSQL has a developer’s room and Simon Riggs just wrapped up a talk about Replication. I sincerely hope that the video of the talk turned out well, because it was the most inspiring and technically interesting talk I have seen in a very long time. Unfortunately, I don’t have a copy of the slides at the moment, but word is that they will be posted on the BSD wiki soon.

Simon focused on new features in 8.4 that affect file-based replication, also mentioning streaming, synchronous replication — which will not be included in 8.4, but is being actively worked on. He explained his rationale for objecting to the inclusion of the synchronous replication patches, mostly, I think, based on the complexity of the WAL archiving required as it was implemented.

Then, Simon launched into an in-depth tour of the issues and solutions brought about during his team’s work on Hot Standby. Hot Standby allows read-only queries to be made against a file-based replication enabled Postgres server, known as Point-in-time recovery and WAL Shipping in the Postgres documentation.

Simon started work on PITR-related patches about five years ago, and continues that work with others today.

One fascinating aspect of the hot standby patches is that they ultimately caused performance improvements in sub-transactions across the board – and will likely cause up to 5% improvement in that code path. There were other performance improvements, but I’ll wait for the slides to mention those. At several times during the talk, Simon pointed out features that Postgres has that no other database has — such as multiple options for dealing with conflicts in hot standby (freezing, conflict resolution and timeout).

At the end of the talk, Simon spent a few minutes talking about how Postgres is capable of being the best database, not just the best open source database. And how all the people in the room were capable of contributing as he had. He claimed that prioritization and aiming to work on the biggest, most interesting problem you can are all you need. And he claimed that all that made him different was that he was a little more persistent about solving problems.

Rock on, Simon.

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What are you waiting for? Get your PgCon talks in now!


Yes, that’s me, with Tom Lane. You, too, might be able to get your picture with Tom!

Like Josh Berkus said yesterday:

As of today, you have 2 weeks left to submit talk proposals to PGCon.

You know you want to. PGCon is the international conference for PostgreSQL hackers, sysadmins, application developers, SQL geeks and other Smart People. Submit your talk! Be a Smart Person too!

PGCon will be happening May 21-22 in Ottawa, Canada, with tutorials on May 19 and 20. Some financial help is often available for speakers, but none is available for non-speakers. So submit, submit!

We particularly could use some talks on the new 8.4 features, really creative PostgreSQL applications, massive Postgres scaling, PostGIS, BioPostgres, and a few case studies. This means you.

I attended PgCon last year for the first time. Not only were the presentations top notch, but Dan Langille‘s hospitality set the groundwork for yet another fantastic community-building experience PostgreSQL community members experienced during the 2006 Anniversary summit in Toronto, again in 2007 at the first PgCon.

We had plenty of outstanding socializing and hacking opportunities. Last year’s conference started with a gathering of committers that was fodder for great pub and hallway track conversation all week. Great talks I saw included Andrew Sullivan’s Idle thoughts on PostgreSQL Project Management, Greg Sabino Mullane’s Bucardo talk about this multi-master replication tool, and Magnus Hagander’s walk through how search.postgresql.org was implemented.

Ottawa was beautiful last year, and I can’t wait to go back this May!

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A year of PDXPUG

Last year was the third year that PDXPUG has been operating in Portland, and I decided to look back at our year of meetings. Here goes:

January 11 – 10 things you can use in PostgreSQL 8.3
February 26 – Extreme Database Makeover: RT
March 20 – Managing Internet Services: Using the right tool for the job
April 17 – Rails on PostgreSQL
May 15 – PostgreSQL for Pythoneers
June 19 – The relational model
July 20 – PDXPUG DAY!, and the schedule
August 21 – Tsearch2 and Materialized Views (Guest speaker from Seattle!!)
September 18 – The Visual Planner
October 16 – Point In Time Recovery
November 20 – Reviewed 8.4 features with the help of depesz’s blog
December – Coder’s Social

Thanks everyone who gave talks and attended meetings! User groups are only as good as the people who participate in them, and this list shows just how talented, diverse and fun the Postgres community is in Portland. I love you guys!

Looking forward – once again, we’ve already scheduled talks through the next four months! I feel like the group is running on its own momentum, and that is a fabulous feeling. We have a data visualization talk, another Extreme Database Makeover, and hopefully a presentation about teaching database theory with PostgreSQL.

Our next meeting is on January 15, 7pm with Stephen Jazdzewski traveling all the way from Eugene to present SplendidCRM, a formerly Microsoft SQL-only system that is now compatible with PostgreSQL. I am happy to see more of our Microsoft colleagues joining and presenting to the user group communities, as I’ve always felt they are underrepresented in our groups. Also, I’m happy to host another out-of-town presenter here in Portland! Hope to see you on the 15th.

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Postgres mailing list traffic over time

Code vs. Docs

Graph by Magnus Hagander

Spurred on by Bruce’s recent blog post, I spotted a fun thread on pgsql-general:

http://archives.postgresql.org/pgsql-general/2008-11/msg01026.php

A few core contributors have been examining their archives and speculating why it is that some feel that they can’t keep up with mailing list traffic as well as they used to.

Reasons tossed around included:

  • More people involved
  • More patches
  • Contributors are just getting older
  • More in-depth questions. Tom said: “Fewer, How do you pronounce Postgres? and more, Explain the various isolation levels for transactions and how does that affect my particular situation?”

Out came the graphs! Tom Lane kicked things off initially with a plot of mailing list messages since 1998:

Tom Lane

I shared one of Magnus’ graphs about Code vs. Documentation at the top. There are several more graphs shared in that thread that are worth checking out, along with pointers to resources like MarkMail, graphs from Ron Mayer, and Ohloh. Enjoy!

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Mentor Summit Report for PostgreSQL

mentor summit

Update: Fixed the etherboot wiki link.

I attended the Google Summer of Code Mentor Summit this past weekend on behalf of PostgreSQL. We met at the Google campus in Mountain View.

This event was an unconference and so, none of the sessions were determined in advance.

Some of the highlights were:

  • Leslie Hawthorn and Chris DiBona went into some detail with the whole group about the selection process for GSOC. This session made me feel as though PostgreSQL had relatively good chances for being accepted again next year. Google, however, does not pre-announce projects/products, so there is no sure thing about our (or any other project’s) involvement.
  • I met MusicBrainz guys and was pleased to receive many bars of chocolate they requested to be distributed to SFPUG and PDXPUG members as thanks for making an great database.
  • Attended three sessions concerning recruitment and retention of students. This is a topic that many people were interested in, but that few people feel they have a proper strategy for.

I also led a session on recruitment and retention of students to open source projects. Some of the ideas that came out of that and the related sessions were:

  • Determine what makes you personally need to be part of Postgres (joy of learning, scratching a technical itch, making a tool for your job, fame). Find out which of those things your student also needs or wants and try to give that or help your student achieve that thing.
  • Have a clearly defined method for students to keep journals. Several projects simply used MediaWiki and templates.
  • Use git (or other distributed revision control), and have students commit early and often to a branch that mentors have access to.
  • The Etherboot project has a great system: http://etherboot.org/wiki/soc/2008/start
  • Hold weekly meetings over IRC. These can be brief, but help get students accustomed to your project’s culture and way of doing things.
  • Ask the student: “are you on track?”, ask the mentor: “do you think the student is on track?” on a weekly basis
  • If you want students to stick around, find incremental responsibilities to assign that are driven by their enthusiasm.
  • Interview on the phone all your students ahead of time, not just the ones you think might be a problem.
  • Require a phone number on the application for the student.
  • Require a secondary contact so that if the student “disappears” there’s a backup person to contact. (and contact that person BEFORE SoC starts)

I made good connections with members of Git, Parrot, WorldForge, Ruby and many other community leaders. I was particularly impressed by the ideas and stories from the current Debian project leader, Steve McIntyre and Gentoo council member Donnie Berkholz. Donnie recommended some books about recruitment that I plan to read and review in the next few weeks.

The issue of mailing list moderation and the number of people required to keep mailing lists functioning properly came up frequently. If you know a moderator for a Postgres mailing list, please consider thanking them for doing a very tedious, extremely important and often thankless job.

I also spent some time discussing with Leslie Hawthorn and Cat Allman how to increase the total number of women mentors and students next year. Leslie and I shared some ideas and I offered to help implement them next year. One thing the crowd asked for was explicit training on how to recruit and manage female students. Realistically, this information will apply to all students, and I hope this training helps us recruit more students overall.

I thought the conference went quite well. I hope PostgreSQL is accepted next year, and that one of our mentors is able to attend this conference. And, if you go, be sure to register for the hotel early, and stay at the Wild Palms.

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PgDay EU – Best conference ever?

PgEU conference Photo
Smiling, PostgreSQL-using conference goers

Anyone who went will likely tell you how much they enjoyed PGDay EU 2008. My biggest regret this year is that I was unable to attend.

Magnus Hagander’s Planet blog is still missing, so I’m blogging the link to his fabulous photos for him. If you see any pictures with missing names or labels, please let him know at magnus -at- hagander (dot) net.

This conference was once again led by Gabriele Bartolini, and a large supporting team – including the other board members of PgEU – Magnus Hagander, Jean-Paul Argudo and Andreas Scherbaum. PgEU (for those that don’t know) is a non-profit dedicated to promoting PostgreSQL in European nations. Next year, this conference will be held somewhere in France! Stay tuned to planet.postgresql.org for details!

Update:

My favorite photo:
lolcats and greg stark

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October is a month of many conferences

wherecamp

I just blogged about WhereCampPDX, and am enjoying a few days of quiet before heading out to Google for the Summer of Code Mentor’s summit this coming weekend.

I was so busy I didn’t have much time to blog about the PostgreSQL Conference West. It was great to see everyone, and I came away more sure than ever that PostgreSQL has the best developer and user community. We had so much fun, and I really enjoyed seeing the creative ways people are using PostgreSQL – for business (Proprietary to PostgreSQL), education (Visual Planner) and as a hobby (PL/LOLCODE).

WhereCampPDX was amazing! I had a couple fantastic conversations with Webb Sprague, a regular PostGIS presenter for PDXPUG and Portland PostgreSQL conferences. He’s interested in getting people together to talk about anthropology and tech, and how to better meet the needs of the people who will actually end up using disaster management software in a crisis. Look for a fabulous event from him this spring!

As far as GSOC, I’m hoping to take a lead role in this next year with Josh Berkus‘ help. He’s managed Summer of Code for at least two years, and has worked hard to match mentors and students, and we’ve ended up with several excellent contributions.

My plan for PostgreSQL is to start early on recruitment and project proposals, so that we have an excellent turnout next year. So, if you know of a project you want worked on, or know of students who would be good candidates – let’s get in touch now and start recruiting!

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PostgreSQL Conference: Friday night dinner

taking shots
How to have fun, PostgreSQL-style

Those of you in town on Friday evening are welcome to join us at Paddy’s at 6pm for dinner:

Paddy’s Bar & Grill
65 SW Yamhill St
Portland, OR 97204

The reservation is under ‘Selena’, and we’ll be sitting in the front. The MAX runs directly in front of the restaurant.

Food is good – vegetarian-friendly, but not necessarily vegan or gluten-free. Those looking for those types of food options, let me know – there are actually excellent places nearby to eat, and you could join us a little later for socializing after a proper meal.

I’ll be directing those that want dinner at the Code Sprint over there – so I asked for 20 seats. Please comment or email me if you plan to attend, so that I can ask for more space if we fill up.

This isn’t a sponsored dinner – so we’ll all go dutch, unless a generous member of a company would like to sponsor us 🙂

I imagine several members of PDXPUG will be there. Can’t wait to see you all!