[GTALUG-Announce] GTALUG Meeting on Tuesday 13 February at 7:30pm

[hi at gtalug.org]

<http://gtalug.org/meeting/2018-02/>

# Postgres, MVCC, and You (or, why COUNT(*) is slow) with David Wolever

It's hard to be a developer today without using a database… but they're often surrounded by an air of reverent mystery.

One of those mysteries is why it's so slow to count all the rows in a table using COUNT(*). After all, it's just a matter of walking a b-tree and counting leaves… and that should be trivial to optimize!

In this talk I'll answer the question of "why COUNT(*) is slow" by taking a deep dive into the the internals of Postgres' MVCC implementation, looking at:

    The question of "why COUNT(*) is slow"
    The on-disk storage layout and why, under the hood, it's not a b-tree
    What Postgres means by MVCC, with examples of the utility of transactions
    Introduce xid, xmin, xmax
    Discuss tuple visibility
    Explain VACUUM and xid wraparound
    Show off transaction isolation levels

This talk is accessible to anyone who's used an SQL database, with enough depth that experienced developers will find some interesting tidbits.

About me: David is a Pythonista from Toronto, Canada. He's co-founder of both PyCon Canada – Canada's regional Python conference – and Akindi.com – a small company that's making multiple-choice bubble sheet tests a little bit less terrible. He's also the author of nose-parameterized, a parameterized testing for every Python testrunner, and pprint++, a Python pretty-printer that's actually pretty. Say hi on Twitter: @wolever!


## Location

George Vari Engineering and Computing Centre
245 Church Street, Room 203
Ryerson University

<http://goo.gl/maps/16oJ2>

<http://www.openstreetmap.org/way/23447525>

## Schedule

* 6:00 pm - Please discuss on the general mailing list (i.e. <talk at gtalug.org>) where you want to go for dinner.
* 7:30 pm - Meeting and presentation.
* 9:00 pm - After each meeting, a group of GTALUGers move to The Imperial Pub (54 Dundas St East) for refreshments and more socialising.

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