§ PostgreSQL

The Flynn Postgres appliance provides PostgreSQL 9.5 in a highly-available configuration with automatic provisioning. It automatically fails over to a synchronous replica with no loss of data if the primary server goes down.

§ Usage

§ Adding a database to an app

Postgres comes ready to go as soon as you’ve installed Flynn. After you create an app, you can provision a database for your app by running:

flynn resource add postgres

This will provision a database on the Postgres cluster and configure your application to connect to it.

§ Connecting to the database

Provisioning the database will add a few environment variables to your app release. PGDATABASE, PGUSER, PGPASSWORD, and PGHOST provide connection details for the database and are used automatically by many Postgres clients.

Flynn will also create the DATABASE_URL environment variable which is utilized by some frameworks to configure database connections.

§ Connecting to a console

To connect to a psql console for the database, run flynn pg psql. This does not require the Postgres client to be installed locally or firewall/security changes, as it runs in a container on the Flynn cluster.

§ Dumping and restoring

The Flynn CLI provides commands for exporting and restoring database dumps.

flynn pg dump saves a complete copy of the database schema and data to a local file.

$ flynn pg dump -f latest.dump
60.34 MB 8.77 MB/s

The file can be used to restore the database with flynn pg restore. It may also be imported into a local Postgres database that is not managed by Flynn with pg_restore:

$ pg_restore --clean --no-acl --no-owner -d mydb latest.dump

flynn pg restore loads a database dump from a local file into a Flynn Postgres database. Any existing tables and database objects will be dropped before they are recreated.

$ flynn pg restore -f latest.dump
62.29 MB / 62.29 MB [===================] 100.00 % 4.96 MB/s
WARNING: errors ignored on restore: 4

This will generate some warnings, but they are generally safe to ignore.

The restore command may also be used to restore a database dump from another non-Flynn Postgres database, use pg_dump to create a dump file:

$ pg_dump --format=custom --no-acl --no-owner mydb > mydb.dump

§ External access

An external route can be created that allows access to the database from services that are not running on Flynn.

flynn -a postgres route add tcp --service postgres --leader

This will provision a TCP port that always points at the primary instance.

For security reasons this port should be firewalled, and it should only be accessed over the local network, VPN, or SSH tunnel.

§ Extensions

The Flynn Postgres appliance comes configured with many extensions available including hstore, PostGIS, and PLV8. To enable an extension, use CREATE EXTENSION:

$ flynn pg psql
psql (9.5.1)
Type "help" for help.

bbabc090024fcdd118b04c50a0fb0d8c=> CREATE EXTENSION hstore;

This is a complete list of the extensions that are available:

Name Version Description
btree_gin 1.0 support for indexing common datatypes in GIN
btree_gist 1.0 support for indexing common datatypes in GiST
chkpass 1.0 data type for auto-encrypted passwords
citext 1.0 data type for case-insensitive character strings
cube 1.0 data type for multidimensional cubes
dblink 1.1 connect to other PostgreSQL databases from within a database
dict_int 1.0 text search dictionary template for integers
earthdistance 1.0 calculate great-circle distances on the surface of the Earth
fuzzystrmatch 1.0 determine similarities and distance between strings
hstore 1.3 data type for storing sets of (key, value) pairs
intarray 1.0 functions, operators, and index support for 1-D arrays of integers
isn 1.0 data types for international product numbering standards
ltree 1.0 data type for hierarchical tree-like structures
pg_prewarm 1.0 prewarm relation data
pg_stat_statements 1.2 track execution statistics of all SQL statements executed
pg_trgm 1.1 text similarity measurement and index searching based on trigrams
pgcrypto 1.1 cryptographic functions
pgrouting 2.0 pgRouting Extension
pgrowlocks 1.1 show row-level locking information
pgstattuple 1.2 show tuple-level statistics
plpgsql 1.0 PL/pgSQL procedural language
plv8 1.4.2 PL/JavaScript (v8) trusted procedural language
postgis 2.1.5 PostGIS geometry, geography, and raster spatial types and functions
postgis_topology 2.1.5 PostGIS topology spatial types and functions
postgres_fdw 1.0 foreign-data wrapper for remote PostgreSQL servers
tablefunc 1.0 functions that manipulate whole tables, including crosstab
unaccent 1.0 text search dictionary that removes accents
uuid-ossp 1.0 generate universally unique identifiers (UUIDs)

Additionally, the following full text search dictionaries are installed by default:

Name Description
danish_stem snowball stemmer for danish language
dutch_stem snowball stemmer for dutch language
english_stem snowball stemmer for english language
finnish_stem snowball stemmer for finnish language
french_stem snowball stemmer for french language
german_stem snowball stemmer for german language
hungarian_stem snowball stemmer for hungarian language
italian_stem snowball stemmer for italian language
norwegian_stem snowball stemmer for norwegian language
portuguese_stem snowball stemmer for portuguese language
romanian_stem snowball stemmer for romanian language
russian_stem snowball stemmer for russian language
simple simple dictionary: just lower case and check for stopword
spanish_stem snowball stemmer for spanish language
swedish_stem snowball stemmer for swedish language
turkish_stem snowball stemmer for turkish language

§ Safety

This appliance is designed to provide full consistency and partition tolerance for all operations that are committed to the write-ahead log (WAL). Note that this guarantee does not apply to advisory locks, as they are specific to the server they are acquired and are not persisted to the WAL.

There is currently no support for tuning, and data transfer during recovery is not optimized, so we do not recommend using the appliance for applications that have high throughput or many records.