Postgres for MySQL (and other database) people

Postgres
(for non-Postgres people)
Greg Sabino Mullane
End Point Corpora=on
greg@endpoint.com

SELECT SUM(info) FROM talk;
•  Postgres philosophy and history
•  Conversion advice
•  Postgres gotchas
•  Postgres limitaCons and features
•  OrganizaCon and community
•  Development and infrastructure

The Part of Whys
•  Why MySQL?
•  Why Postgres?
•  Why me?
•  Why you?

•  Postgres? PostgreSQL? Postgre? PostgresSQL?
•  Philosphy
•  Mercifully quick history lesson

MigraCng Your App
•  Schema
•  Data
•  ApplicaCon
•  Support

MigraCon : Schema
•  Mysqldump?
•  --compatible=postgresql --no-data
•  Redesign
•  Conversion tools

MigraCon : SQL Spec
•  Who cares?
•  Postgres vs. the spec
•  MySQL vs. the spec
•  Oracle vs. the spec
•  DB2 vs. the spec
•  MSSQL vs. the spec

MigraCon : Schema
•  Tables
•  Engines and plugins
•  CustomizaCon

MigraCon : Schema : Data Types : Numbers
•  INTEGER (smallint, bigint, serial)
•  NUMERIC (double precision, money)
•  REAL

MigraCon : Schema : Data Types : Text
•  TEXT
•  VARCHAR(n)
•  CHAR(n)

MigraCon : Schema : Data Types : Dates
•  DATE
•  TIMESTAMPTZ
•  TIME
•  INTERVAL

MigraCon : Schema : Data Types : Boolean
•  BOOL
•  TRUE, ‘t’, ‘y’, ‘yes’, ‘on’, 1
•  FALSE, ‘f’, ‘n’, ‘no’, ‘oﬀ’, 0

MigraCon : Schema : Data Types : Binary
•  BYTEA
•  Internal or external?

MigraCon : Schema : Data Types : Others
•  Geometric (line, path, box, circle, polygon)
•  Arrays
•  ENUM
•  CIDR, INET, MACADDR
•  UUID
•  XML

MigraCon : Schema : Sequence
•  Auto‐increment
•  SEQUENCE
•  SERIAL
•  INTEGER NOT NULL DEFAULT nextval(‘foo’)

MigraCon : Schema : DEFAULT
•  cdate TIMESTAMPTZ NOT NULL DEFAULT now()
•  (almost) anything at all
•  No magic

MigraCon : Schema : FOREIGN KEYS
•  Fully supported
•  ON DELETE CASCADE
•  ON DELETE RESTRICT
•  ON DELETE SET NULL
•  ON DELETE SET DEFAULT
•  DEFERRED INITIALLY DEFERRED

MigraCon : Schema : Indexes
•  CREATE INDEX foo ON mytab(mycol);
•  CREATE INDEX foo2 ON mytab(mycol) WHERE size
= ‘grande’;
•  CREATE INDEX foo3 ON mytab(LOWER(blurb));
•  CREATE INDEX foo4 ON mytab(LOWER(blurb))
WHERE size = ‘grande’;

MigraCon : Schema : Indexes
•  CREATE INDEX CONCURENTLY foo ON
mytab(mycol);
•  No rebuilding of tables
•  Reverse scan, bitmap

MigraCon : Schema : Triggers
•  CREATE TRIGGER mytrig BEFORE INSERT OR
DELETE OR UPDATE ON mytab FOR EACH ROW
EXECUTE PROCEDURE somefunc();
•  Aside: funcCons and languages

MigraCon : Schema : FuncCons
•  Very custom
•  Pl/PGSQL == Pl/SQL
•  Very powerful

MigraCon : Data
•  No autocommit, fsync oﬀ, no autovacuum
•  COPY vs. INSERT
•  Turn oﬀ indexes and triggers (FK)
•  ANALYZE

ANALYZE
•  Cost‐based planner
•  Autovacuum
•  IniCal load
•  Default_staCsCcs_target
–  10
–  100
–  1000
–  More?

VACUUM
•  MVCC – Oracle vs. Pg
•  Rollback segment
•  Concurrency and locking
•  Table bloat
•  VACUUM FULL, CLUSTER, REINDEX

MigraCon : ApplicaCon
•  aka SQL
•  Clients (PHP excepCon)
•  SQL modes
–  TradiConal
–  Postgresql
•  “Any client can change its own session
sql_mode value at any Cme.”

MigraCon : SQL : NULL
•  NULL is NULL

MigraCon : SQL : SELECT
•  Query planner
•  JOINS
•  Subselects

MigraCon : SQL : GROUP BY
•  SELECT a,b,c FROM mytab GROUP BY a,b
•  Standard or not?
DISTINCT ON

MigraCon : SQL : Text match
•  CHAR / VARCHAR / TEXT case sensiCve
•  SELECT count(*) FROM mytab WHERE mycol =
‘Fred’;

•  …WHERE LOWER(mycol) = ‘fred’;

MigraCon : SQL : full text search
•  Tsearch2: contrib vs. core
•  Powerful, complex
•  TransacConal!

MigraCon : SQL : DELETE
•  One table only
•  No LIMIT, no ORDER BY
•  No QUICK, LOW PRIORITY, IGNORE
•  DELETE FROM ONLY mytab WHERE…
•  DELETE FROM mytab USING otab WHERE
mycol = otab.id AND otab.size = 'foo';
•  DELETE FROM mytab WHERE mycol IN (SELECT
id FROM otab WHERE size = ‘foo’);

MigraCon : SQL : UPDATE
•  Only one table
•  No ORDER BY, LIMIT, etc.
•  UPDATE mytab SET mycol=123 FROM otab
WHERE mycol = otab.id AND otab.size = ‘foo’;

MigraCon : SQL : INSERT
•  Only one table
•  No REPLACE or ON DUPLICATE KEY UPDATE
•  UPSERT via plpgsql or app logic
•  DEFAULT
•  INSERT INTO mytab DEFAULT VALUES

MigraCon : SQL : ||
•  Ugh
•  CONCAT
•  Wrapper funcCons
•  NULL an empty string

MigraCon : SQL: GRANT
•  ..and REVOKE
•  Almost any object
•  Immediate eﬀect

MigraCon : SQL : locking
•  Use sparingly
•  Share, exclusive
•  Advisory
•  ALTER TABLE, REINDEX, VACUUM FULL

MigraCon : SQL : Aliases
•  AS opConal but recommended
•  SELECT SUM(mycol) AS mysum
•  SELECT * FROM pg_class c, mytab t…

MigraCon : SQL : Advanced
•  WITH
•  Windowing
•  Recursive funcCons

MigraCon : Support
•  RouCne stuﬀ: autovacuum
•  Monitoring (check_postgres)
•  Backups (MVCC based)

Postgres : Quirks : lowercase
•  Implicit case folding
•  CREATE TABLE abc (A int);
•  CREATE TABLE ABC (a int);
•  CREATE TABLE “abc” (“a” int);
•  CREATE TABLE “ABC” (“A” int);
•  SELECT * FROM “ABC” WHERE “A”=123;

Postgres : Quirks : CasCng
•  8.3 removed some implicit casts
•  SELECT 1 = ‘1’::text;
•  ERROR: operator does not exist: integer=text
•  1. Fix the app
•  2. Add the casts back in

Postgres : Quirks : COUNT(*)
•  MyISAM vs INNODB
•  Use an index
•  Triggers
•  SELECT reltuples FROM pg_class WHERE
relname = ‘foo’;

Postgres : Quirks : Schemas
•  Database versus schemas versus cluster
•  Changes are cheap
•  No name‐based schemas
•  The ‘public’ schema
•  contrib/dblink

Postgres : Quirks : vacuum
•  Newer the berer
•  autovacuum

Postgres : Quirks : i18n
•  SQL_ASCII vs UTF‐8
•  Per database only

Postgres : Quirks : Hints
•  No hints per se
•  Smart planner
•  SET enable_* EXPLAIN
•  Few other knobs – per cluster

Postgres : Quirks : Rules
•  Last resort. ‘nuﬀ

Postgres : Drawbacks
•  ReplicaCon pg_upgrade
pg_upgrade

•  In‐place upgrade (pg_migrator, Bucardo)
•  Tuned for a toaster
•  Name
•  Publicity and markeCng

Postgres : Strengths
•  Custom everything
•  TransacConal DDL
•  PostGIS
•  Query planner
•  Support
•  AuthenCcaCon: pg_hba.conf
–  PAM, ident, Kerberos, LDAP, …

Postgres : OrganizaCon
•  Who?
•  Transparent meritocracy
•  “core”
•  Commirers
•  Mailing list, IRC, wiki
•  Company roles
•  Spread the risk
•  Cannot be bought (assets or people)

Postgres : Community
•  Core vs. “core”
•  Pgfoundry, github, bucardo.org, …
•  PostGIS
•  Mailing list? Bug report? User?
•  InteracCon!
•  Wiki, advocacy, sysadmin, docs, packagers
•  Clients, tools, replicaCon systems
•  Volunteers (IRC)

Postgres : Infrastructure
•  See Dave’s talk later today
•  Servers, companies
•  Build farm
•  Wiki
•  Commisest

Postgres : Development
•  Show me the money!
•  Individual developers vs. companies
•  CVS vs. git git wins! :)
git wins!
•  Commirers vs. patchers vs. reviewers

Postgres : Version
•  Roughly every year
•  8.3 8.3.10
•  Major version, minor version, revision
•  Naming a version

Postgres : Patches
•  Bug report, mailing list post, TODO list
•  Run up the flagpole (Tom Lane test)
–  Stable?
–  Useful?
–  Spec compliant?
–  Side effects?
–  Best approach to problem?
•  Diff format, formaung, docs
•  Added to patch queue, commisest
•  Patch reviewer
•  Commit (20 vs 300)

Postgres : Patches
•  About that ﬂagpole…
•  High standards
•  Cming
•  dfS

Postgres : Licensing
•  BSD (or MIT) PostgreSQL license
•  Free as in speech
•  Free as in beer
•  Plays well with others (PostGIS)

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