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DrupalHugs.html
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<!DOCTYPE html>
<html>
<head>
<title>Drupal Hugs</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
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<textarea id="source">
layout: true
<div class="acquia-header"><img src="acquia_logo.png" style="height: 25px;"/></div>
<div class="acquia-footer"><span>Emily Slocombe and Pim van der Wal</span></div>
---
class: center, middle
name: section-begin
 
 
 
 
 
# Drupal just wants to
# _hug_
# your database
---
class: center, middle
name: section-begin
# And by _hug_ -- I mean bodyslam
???
Drupal can really abuse a database
---
class: center, top, toc
## Table of Contents
| |
| -------------------------- |
| What is Drupal? |
| Top complaints |
| MySQL at Acquia |
| Caching |
| Drupal things |
| Common tables |
| Common issues |
| Your role |
???
stuff
---
## What is Drupal?
* a Content Management System
* you probably have been on a drupal site, today even
* https://www.drupal.com/showcases
.center[<img src="showcase.png" width="60%">]
???
GET NEW SCREENSHOT !
As a very flexible CMS, it can either be really lean or bloated with modules.
We host thousands of Drupal sites, and they all look and perform very differently from each other.
* contrib and core modules. Sites are basically completely changed with how they look and run
---
## Drupal versions
* Initial release in 2000
* Drupal 6 (2008)
* Drupal 7 (2011)
* Drupal 8 (2015)
???
* Drupal 8 was released very recently. Most of the sites we host are on version 7.
* Acquia still hosts Drupal 6, 7 and 8 sites.
---
## Top complaints
* bad queries
* 'views'
* misinformation
???
* Bad queries, like those generated by views
* When people hear that I work with Drupal and they are aware at all of what the queries can look like, I often get semi-disgusted responses. Drupal views is a query builder and it doesn't always build the most beautiful queries.
* I also had one person 'inform me' that Drupal couldn't use InnoDB -- telling me the story of how their site broke when they tried. Whatever happened for them, completely ruined their opinion of Drupal. I've been with Drupal since version 5, and I can safely say I have never had it 'not work' on InnoDB.
---
## MySQL at Acquia
* all AWS EC2
* Percona Server 5.5 (working on upgrades)
* EBS backed MySQL (slowww disks)
* master-master (active-passive)
* dns-based failover
* thousands of db servers, 2.3 DBAs
???
* we are running with only one active in the master-master pair
* the dbs's are part of the operations team.
* the sites we run range from super small from like the 'librarians of nebraska fan site' to huge like major media news sites and I just made up that nebraska thing
---
## Caching
* Always avoid the database
- < drupal 8 defaults to no caching. Enable page cache
- all caching defaults to in-database
- use memcached for cache backend
* Cache layers at Acquia:
.center[]
???
* The biggest performance tip is 'Caching'
* Drupal basically loads websites from the database. Cache more, hit the database less.
* caching exists at each layer of the diagram
---
## Drupal things
* Views
* Blocks
* Panels
* Modules
* Custom fields
???
* these are the basic components of a drupal web page.
---
## Drupal things: a page
???
* here is a recent version of the acquia dot com page
---
## Drupal things: a page
???
* here are those basic drupal components on the acquia dot com web page
---
## Drupal things - Views Module
* Views is essentially a query builder
--
* Part of Drupal Core
--
* Allows non-programmers to generate SQL queries
--
* Defaults to left joins
--
* Views can use other views (sub queries)
???
there should be an example on the next slide of a views-style query with left joins... the classic... pagination!
---
## Drupal things - Views
* Pagination hurts
???
* Subquery
* 3 left joins
* No limit
---
## Drupal things - Views
* Pagination hurts
- Views Litepager (https://www.drupal.org/project/views_litepager)
- Views Load More (https://www.drupal.org/project/views_load_more)
???
Both modules do not show a count and do not allow to go to last page.
---
## Drupal things - Variables
* Drupal configuration table
* Always cached
* Variable contention
???
* Drupal variables are cached so a cache clear and lead each thread to recache the entire variable table
* Modules store aggregate js or css hash in variable table but if that is different per page it will get continuously updated
TODO: discuss this last one with Mark S
---
## Drupal things - Variables
* Cache stampede<br>
.center[]
???
advance to the next slide before everyone gets vertigo!
---
## Drupal things - Variables
* Cache stampede<br>
https://www.drupal.org/project/variables_that_suck_less
???
A cache clear causes the entire vaariable table to be loaded into cache.
---
## Drupal things - Custom fields
* Drupal 6: Custom fields grouped together in tables
* Drupal 7: A separate table per custom field
* Drupal 8: A separate table per custom field
???
Drupal 7 allows separate database engines to be used for custom fields. Drupal 8 does not since it wasn't being used.
---
## Drupal things - Custom fields
Drupal 7 and 8:
* Each custom field is stored in a separate table
* Updating 10 custom fields mean updating 10 records
* Lots of joins
---
## Common tables - Drupal 8 ERD
<img src="Drupal8_UPsitesWeb_Schema_10-19-2013.png" style="width: 100%;"/>
???
* this was how I tried to learn drupal back when I was at Nokia 6 or 7 years ago
* there are no foreign keys
* Joins are based on fake foreign keys!
---
## Common tables
* cache*
* cache_form
* field_*
* field_revision*
* node
* semaphore
* variable
* watchdog
---
## Common tables
* cache* -> memcached
* cache_form -> possibly compression
* field_*
* field_revision*
* node
* semaphore -> sometimes memcached
* variable -> investigate contents
* watchdog -> send to file
???
* cache_form records get way too big. Fixed in d8, working on a fix to d7
* watchdog not necessarily bad, but there a lot of customers that write every lasy bit of info, so it can get too much traffic.
---
## Common tables - cache_form
* cache_form table stores state between pages
- Filters, shopping cart, etc.
* Views store the views object
- In Drupal 7 they can add too much data, fixed in Drupal 8
* Drupal cron purge needs to run
???
* One customer wrote 1.3MB per cache_form record for each page visit. This contained a pre-generated filter for videos.
* Compression can help reduce the disk I/O for large records. Not a huge gain in general.
* Purge job choice between running frequently and causing locking issues or infrequent (once per day) and taking hours to run on busy sites.
---
## Common tables - cache_form
* Compression sometimes helps
<p style="text-align:center"><img src="compressed-denny.png" style="width: 45%"/></p>
---
## Common tables
???
many of our customers use New Relic. Here, they might choose to blame the database for a performance issue.
---
.center[<img src="database.jpg" height="100%">]
---
## Common tables
???
Here we see, perhaps, cache_form is having trouble
---
## Common issues - Capacity
* CPU / memory => EC2 instance upsize
- Bigger InnoDB buffer pool
- More CPU cores<p>
* Disk I/O issues
- InnoDB log file size
- Hard limit of disk I/O capacity
???
* CPU cores are limited to what the version of MySQL supports
* Log file size mostly addresses peak usage and not sustained higher usage
---
## Common issues - Furious flushing
<img src="furious-flushing-redolog.png" alt="Drawing" style="width: 375px;"/>
<img src="furious-flushing-iops.png" alt="Drawing" style="width: 375px;"/>
<img src="furious-flushing-readwrite.png" alt="Drawing" style="width: 375px;"/>
<img src="furious-flushing-innodbwrites.png" alt="Drawing" style="width: 375px;"/>
???
* Yes, 600 IOPS is non-RAID spinning rust EBS
---
## Common issues - Query Cache
<img src="qc1-qcusage.png" alt="Drawing" style="width: 375px;"/>
<img src="qc1-hitrate.png" alt="Drawing" style="width: 375px;"/>
<img src="qc1-prunes.png" alt="Drawing" style="width: 375px;"/>
<img src="qc1-temptables.png" alt="Drawing" style="width: 375px;"/>
???
* Drupal is supposed to be mostly reads, most customers have 99% reads
---
## Common issues - Query Cache
<img src="qc2-qcusage.png" alt="Drawing" style="width: 375px;"/>
<img src="qc2-hitrate.png" alt="Drawing" style="width: 375px;"/>
<img src="qc2-cpu.png" alt="Drawing" style="width: 375px;"/>
<img src="qc2-runningthreads.png" alt="Drawing" style="width: 375px;"/>
---
## Common issues: Traffic
* deploy with cache clear (drush cc all)
* crawlers
* lots of admin edits
* user registrations / auth traffic
* query cache
???
* due to the nature of drupal, certain types of traffic tend to bypass caches and go straight to the db
---
## Common issues: Traffic
---
## Common issues: Traffic
* deploy with cache clear (drush cc all)
- maint mode
* crawlers
- deflect upstream
* lots of admin edits -> semaphore, *revision
- perhaps make an edit web node, reserved
* user registrations / auth traffic
- fix everything and scale
* query cache (watch throughput and thread status)
- increase - yes, really, sometimes.
- zero + mutex
---
## Your role
---
## Your role
* not often fixing queries or adding indexes
- it is code, we can't easily change code
* monitor workload
- statsd
- new relic
- whatever
* provide useful feedback to developers
- more than just slow queries
* where are they being generated?
---
class: left, bottom, chapter-header
### I am sure there are none.
## questions?
---
class: left, bottom, chapter-header
### For not falling asleep
## Thank you!
---
## extra1 - cache_form cron fail
---
## extra2 - cache_form crawler fail
---
## extra3 - Long Transactions
<img src="trx-trx.png" alt="Drawing" style="width: 375px;"/>
<img src="trx-runningthreads.png" alt="Drawing" style="width: 375px;"/>
<img src="trx-historylist.png" alt="Drawing" style="width: 375px;"/>
<img src="trx-slow.png" alt="Drawing" style="width: 375px;"/>
<!--## Very Wise Words!
 
 
 
 
 
#### .center[Make Sure Your Backup Architecture Meets Your Business Requirements]
##### .center[(so we never have to do a recovery)]
-->
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