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Life on a_rollercoaster

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Dealing with large databases is always a challenge. The backups and the HA procedures evolve meanwhile the database installation grow up over the time.

The talk will cover the problems solved by the DBA in four years of working with large databases, which size increased from 1.7 TB single cluster, up to 40 TB in a multi shard environment.

The talk will cover either the disaster recovery with pg_dump and the high availability with the log shipping/streaming replication.

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Life on a_rollercoaster

  1. 1. Life on a rollercoaster Scaling the PostgreSQL backup and recovery Federico Campoli Transferwise 2 November 2016 Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 1 / 52
  2. 2. Table of contents 1 2012 - Who am I? What I’m doing? 2 2013 - On thin ice 3 2014 - The battle of five armies 4 2015 - THIS IS SPARTA! 5 2016 - Breathe 6 Wrap up Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 2 / 52
  3. 3. Warning! The story you are about to hear is true. Only the names have been changed to protect the innocent. Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 3 / 52
  4. 4. Dramatis personae A brilliant startup ACME Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 4 / 52
  5. 5. Dramatis personae The clueless engineers CE Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 5 / 52
  6. 6. Dramatis personae An elephant on steroids PG Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 6 / 52
  7. 7. Dramatis personae The big cheese HW Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 7 / 52
  8. 8. Dramatis personae The real hero DBA Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 8 / 52
  9. 9. In the beginning Our story starts in the year 2012. The world was young and our DBA started a new brilliant career in ACME. After the usual time required by the onboarding, to our DBA were handed the production’s servers. Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 9 / 52
  10. 10. Table of contents 1 2012 - Who am I? What I’m doing? 2 2013 - On thin ice 3 2014 - The battle of five armies 4 2015 - THIS IS SPARTA! 5 2016 - Breathe 6 Wrap up Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 10 / 52
  11. 11. 2012 - Who am I? What I’m doing? Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 11 / 52
  12. 12. Size does matter PG, our powerful and friendly elephant was used for storing the data in a multi shard configuration. Not really big actually but very troubled indeed! A small logger database - 50 GB A larger configuration and auth datababase - 200 GB Two archive db - 4 TB each One db for the business intelligence - 2 TB Each db had an hot standby counterpart hosted on less powerful HW. Our story tells the life of the BI database. Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 12 / 52
  13. 13. The carnival of monsters In the early 2013 our brave DBA addressed the several problems found on the current backup and recovery configuration. Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 13 / 52
  14. 14. Lagging standby Suboptimal schema. Churn on large tables and high wal generation rate The slave lagged just because there was autovacuum running rsync used in archive command. The wal were archived over the network using rsync+ssh The *.ready files in the pg xlog increased the risk of the cluster’s crash. Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 14 / 52
  15. 15. Base backup Rudimentary init standby script. Just a pg start backup call followed by a rsync between the master and the slave The several tablespaces were synced using a single rsync process with the –delete option Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 15 / 52
  16. 16. Slow dump Remote pg dump. Each cluster was dumped remotely on a separate server using the custom format. The backup server had limited memory and cpu Dump time between 3 hours and 2 days depending on the database size The BI database was dumped on a daily basis, taking 14/18 hours. Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 16 / 52
  17. 17. Table of contents 1 2012 - Who am I? What I’m doing? 2 2013 - On thin ice 3 2014 - The battle of five armies 4 2015 - THIS IS SPARTA! 5 2016 - Breathe 6 Wrap up Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 17 / 52
  18. 18. 2013 - On thin ice Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 18 / 52
  19. 19. Parallel rsync Our DBA took the baby step approach. He started fixing one issue at a time without affecting ACME’s activity. The first enhancement was the init backup script. Two bash arrays listed the origin and destination’s tablespaces An empty bash array stored the rsync pids The script started the pg start backup For each tablespace a rsync process were spawned and the pid was stored in the third array A loop checked that the pids were present in the process list When all the rsync finished pg stop backup were executed An email to DBA was sent to tell him to start the slave Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 19 / 52
  20. 20. Local archive The high rate of wal generation required a different archive strategy. The archive command changed to a local copy A simple rsync script copied every minute the archives to the slave The script queried remotely the slave for the last restartpoint The restartpoint was used by pg archivecleanup on the master Implementing this solution solved the *.ready files problem but the autovacuum still caused high lag. Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 20 / 52
  21. 21. Autovacuum tune down DBA investigated the autovacuum issue and finally addressed the cause. The high lag on the slave was caused when autovacuum (or vacuum) hit a table concurrently updated. This behaviour is normal and is caused by the standby code’s design. With large denormalised tables which are updated constantly the only workaround possible was to increase autovacuum cost delay with a large value (1 second or more). When the autovacuum process reached an arbitrary cost during the execution there was a 1 minute sleep before the activity resumed. . The lag on the standbys disappeared at the cost of longer autovacuum runs. Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 21 / 52
  22. 22. In the meanwhile... The CE decided to shard the business intelligence database using the hot standby copy The three new databases initially had the same amount of data which was slowly cleaned up later But even with one third of data on each shard, the daily dump was really slow at the point of overlapping over the 24 hours Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 22 / 52
  23. 23. A slowish dump pg dump connects to the running cluster like any other backend; it pulls out data using in the copy format With the custom format the compression happens on the server where pg dump runs The backup server were hammered on the network and the cpu Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 23 / 52
  24. 24. You got speed! Our DBA wrote a bash script doing the following steps Dump the database in custom format locally Generate the file’s md5 checksum Ship the file on the backup via rsync Check the remote file’s md5 Send a message to nagios for success or failure The backup time per each cluster dropped dramatically to just 5 hours including the copy and the checksum verification. Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 24 / 52
  25. 25. Growing pains Despite the business growth the CE ignored the problems with the poor schema design. Speed was achieved by brute force using expensive SSD storage The amount of data store in the BI db increased The only accepted solution was to create new shards over and over again By the end of 2013 the BI databases total size was 15 TB Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 25 / 52
  26. 26. In the meanwhile... Our DBA upgraded all the PG to the version 9.2 with pg upgrade THANKS BRUCE!!!!! Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 26 / 52
  27. 27. Table of contents 1 2012 - Who am I? What I’m doing? 2 2013 - On thin ice 3 2014 - The battle of five armies 4 2015 - THIS IS SPARTA! 5 2016 - Breathe 6 Wrap up Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 27 / 52
  28. 28. 2014 - The battle of five armies Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 28 / 52
  29. 29. Bloating data Q1 2014 opened with another backup performance issue The dump size increased over the time The database CPU usage increased constantly with no apparent reason Most of the shards had the tablespace usage at 90% Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 29 / 52
  30. 30. Mostly harmless Against all odds our DBA addressed the issue. The table used by the BI database was causing the bloat The table’s design was technically a materalised view The table was partitioned in some way Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 30 / 52
  31. 31. Mostly harmless Against all odds our DBA addressed the issue. The table used by the BI database was causing the bloat The table’s design was technically a materalised view The table was partitioned in some way The table had an harmless hstore field Where everybody added new keys just changing the app code And nobody did housekeeping of their data The row length jumped from 200 bytes to 1200 bytes in few months Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 30 / 52
  32. 32. Mostly harmless Against all odds our DBA addressed the issue. The table used by the BI database was causing the bloat The table’s design was technically a materalised view The table was partitioned in some way The table had an harmless hstore field Where everybody added new keys just changing the app code And nobody did housekeeping of their data The row length jumped from 200 bytes to 1200 bytes in few months Each BI shard contained up to 2 billion rows... Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 30 / 52
  33. 33. Just a little trick Despite the impending doom and the CE resistance DBA succeeded in converting the hstore field to a conventional columnar store (SORRY OLEG!). The storage usage dropped by 30% The CPU usage dropped by 60% The speed of ACME’s product boosted ACME saved $BIG BUNCH OF MONEY in new HW otherwise required to shard again the dying databases Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 31 / 52
  34. 34. In the meanwhile... DBA knew the fix was just a workaround He asked the CE to help him in the schema redesign He told them things would be problematic again in just one year Nobody listened Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 32 / 52
  35. 35. Table of contents 1 2012 - Who am I? What I’m doing? 2 2013 - On thin ice 3 2014 - The battle of five armies 4 2015 - THIS IS SPARTA! 5 2016 - Breathe 6 Wrap up Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 33 / 52
  36. 36. 2015 - THIS IS SPARTA! Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 34 / 52
  37. 37. I hate to say that, but I told you so As predicted by our DBA the time required for backing up the BI databases increased again, approaching dangerously the 24 hours. Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 35 / 52
  38. 38. Parallel is da way! Back in the 2013 PG 9.3 added the parallel export. But, to DBA great disappointment, the version 9.3 was initially cursed by some bugs causing data corruption. DBA could not use the parallel dump. However... The parallel backup takes advantage of the snapshot export introduced in the PG 9.2 The debian packaging allows different PG’s major versions on the same machine DBA installed the client 9.3 and used its pg dump to dump the 9.2 in parallel Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 36 / 52
  39. 39. It worked very well... The wrapper script required some adjustments Accept the -j parameter Check if the 9.3+ client is installed Override the format to directory if the parallel backup is possible Adapt the checksum procedure to check the files in the dump directory Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 37 / 52
  40. 40. ...with just a little infinitesimal catch All fine right? Not exactly The restore test complained about the unknown parameter lock timeout The backup hit the speed record since 2013 The schema was still the same of 2013 The databases performance were massively affected with 6 parallel jobs DBA found that with just 4 parallel jobs the databases worked with minimal disruption Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 38 / 52
  41. 41. In the meanwhile... Our DBA upgraded PG to the latest version 9.4. THANK YOU AGAIN BRUCE!!!!! No more errors for the restore test. Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 39 / 52
  42. 42. Table of contents 1 2012 - Who am I? What I’m doing? 2 2013 - On thin ice 3 2014 - The battle of five armies 4 2015 - THIS IS SPARTA! 5 2016 - Breathe 6 Wrap up Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 40 / 52
  43. 43. 2016 - Breathe Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 41 / 52
  44. 44. A new hope The upgrade to PG 9.4 improved the performance issues and DBA had some time to breath. The script to ship the archived wal was improved to support multiple slaves in cascading replica Each slave had a dedicated rsync process configurable with compression and protocol (rsync or rsync +ssh) The script determined automatically the farthest slave querying the remote controlfiles and cleaned the local archive accordingly Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 42 / 52
  45. 45. A new hope The init standby script switched to the rsync protocol The automated restore script used the ALTER SYSTEM added to the PG 9.4 to switch between the restore and production configuration Therefore the restore time improved to at most 9 hours for the largest BI database (4.5 TB) Working with BOFH JR, DBA wrapped the backup script in the $BACKUP MANAGER pre and post execution hooks Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 43 / 52
  46. 46. The rise of the machines In the 2016 Q2, finally, DBA completed the configuration for $DEVOP TOOL and deployed the several scripts to the 17 BI databases with minimal effort. Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 44 / 52
  47. 47. Table of contents 1 2012 - Who am I? What I’m doing? 2 2013 - On thin ice 3 2014 - The battle of five armies 4 2015 - THIS IS SPARTA! 5 2016 - Breathe 6 Wrap up Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 45 / 52
  48. 48. BI database at a glance Year N. Databases Average size Total size Version 2012 1 2 TB 2 TB 9.1 2013 5 3 TB 15 TB 9.2 2014 9 2.2 TB 19 TB 9.2 2015 13 2.7 TB 32 TB 9.4 2016 16 2.5 TB 40 TB 9.4 Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 46 / 52
  49. 49. Few words of wisdom Reading the products source code is always a good practice. Bad design can lead to disasters, in particular if the business is successful. It’s never too early to book the CE to a SQL training course. “One bad programmer can easily create two new jobs a year.” – David Parnas If in doubt ask your DBA for advice. If you don’t have a DBA, get one hired ASAP! Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 47 / 52
  50. 50. Did you say hire? WE ARE HIRING! https://transferwise.com/jobs/ Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 48 / 52
  51. 51. That’s all folks! QUESTIONS? Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 49 / 52
  52. 52. Boring legal stuff LAPD badge - source wikicommons Montparnasse derailment - source wikipedia Base jumper - copyright Chris McNaught Disaster girl - source memegenerator Blue elephant - source memecenter Commodore 64 - source memecenter Deadpool- source memegenerator Thin ice - source Boating on Lake Winnebago Boromir - source memegenerator Sparta birds - source memestorage Dart Vader - source memegenerator Angry old man - source memegenerator Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 50 / 52
  53. 53. Contacts and license Twitter: 4thdoctor scarf Blog:http://www.pgdba.co.uk Brighton PostgreSQL Meetup: http://www.meetup.com/Brighton-PostgreSQL-Meetup/ This document is distributed under the terms of the Creative Commons Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 51 / 52
  54. 54. Life on a rollercoaster Scaling the PostgreSQL backup and recovery Federico Campoli Transferwise 2 November 2016 Federico Campoli (Transferwise) Life on a rollercoaster 2 November 2016 52 / 52

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