Name

sqitchtutorial-vertica - A tutorial introduction to Sqitch change management on Vertica

Synopsis

  sqitch *

Description

This tutorial explains how to create a sqitch-enabled Vertica project, use a VCS for deployment planning, and work with other developers to make sure changes remain in sync and in the proper order.

We'll start by creating a new project from scratch, a fictional antisocial networking site called Flipr. All examples use Git <http://git-scm.com/> as the VCS and Vertica <https://my.vertica.com/> as the storage engine, but for the most part you can substitute other VCSes and database engines in the examples as appropriate.

If you'd like to manage an Vertica database, see sqitchtutorial.

If you'd like to manage an SQLite database, see sqitchtutorial-sqlite.

If you'd like to manage an Oracle database, see sqitchtutorial-oracle.

If you'd like to manage an MySQL database, see sqitchtutorial-mysql.

If you'd like to manage an Firebird database, see sqitchtutorial-firebird.

Connection Configuration

Sqitch requires ODBC to connect to the Vertica database. As such, you'll need to make sure that the Vertica ODBC driver is properly configured. At its simplest, on Unix-like systems, name the driver "Vertica" by adding this entry to "odbcainst.ini" (usually found in "/etc", "/usr/etc", or "/usr/local/etc"):

  [Vertica]
  Description = ODBC for Vertica
  Driver      = /opt/vertica/lib64/libverticaodbc.so

And also creating a "vertica.ini" file in the same directory that contains:

  [Driver]
  DriverManagerEncoding=UTF-16
  ODBCInstLib=/usr/lib64/libodbcinst.so
  ErrorMessagesPath=/opt/vertica/lib64

You might also consider naming your database connection by putting an entry in "odbc.ini" (same directory), like so (assuming that Vertica is running on your local host):

  [dbadmin]
  Description = Vertica dbadmin connection
  Driver = Vertica
  Database = dbadmin
  Servername = localhost
  UserName = dbadmin
  Password = password
  Port = 5433
  Locale = en_US

See the Vertica ODBC Documentation <http://my.vertica.com/docs/7.1.x/HTML/index.htm#Authoring/ConnectingToHPVertica/InstallingDrivers/CreatingAnODBCDataSourceNameDSN.htm> for details. Specific links:

Unix ODBC Configuration <http://my.vertica.com/docs/7.1.x/HTML/index.htm#Authoring/ConnectingToHPVertica/InstallingDrivers/CreatingAnODBCDSNForLinuxSolarisAIXAndHP-UX.htm>
Additional Linux ODBC Configuration ("vertica.ini") <http://my.vertica.com/docs/7.1.x/HTML/index.htm#Authoring/ConnectingToHPVertica/ClientODBC/AdditionalODBCDriverConfigurationSettings.htm>
Windows ODBC Configuration <http://my.vertica.com/docs/7.1.x/HTML/index.htm#Authoring/ConnectingToHPVertica/InstallingDrivers/CreatingAnODBCDSNForWindowsClients.htm>
Mac OS X ODBC Configuration <http://my.vertica.com/docs/7.1.x/HTML/index.htm#Authoring/ConnectingToHPVertica/InstallingDrivers/CreatingAnODBCDSNForMacintoshOSXClients.htm>

Starting a New Project

Usually the first thing to do when starting a new project is to create a source code repository. So let's do that with Git:

  > mkdir flipr
  > cd flipr 
  > git init .
  Initialized empty Git repository in /flipr/.git/
  > touch README.md
  > git add .
  > git commit -am 'Initialize project, add README.'

If you're a Git user and want to follow along the history, the repository used in these examples is on GitHub <https://github.com/theory/sqitch-vertica-intro>.

Now that we have a repository, let's get started with Sqitch. Every Sqitch project must have a name associated with it, and, optionally, a unique URI. We recommend including the URI, as it increases the uniqueness of object identifiers internally, so let's specify one when we initialize Sqitch:

  > sqitch init flipr --uri https://github.com/theory/sqitch-vertica-intro/ --engine vertica
  Created sqitch.conf
  Created sqitch.plan
  Created deploy/
  Created revert/
  Created verify/

Let's have a look at sqitch.conf:

  > cat sqitch.conf
  [core]
        engine = vertica
        # plan_file = sqitch.plan
        # top_dir = .
  # [engine "vertica"]
        # target = db:vertica:
        # registry = sqitch
        # client = vsql

Good, it picked up on the fact that we're creating changes for the Vertica engine, thanks to the "-engine vertica" option, and saved it to the file. Furthermore, it wrote a commented-out "[engine "vertica"]" section with all the available Vertica engine-specific settings commented out and ready to be edited as appropriate.

By default, Sqitch will read sqitch.conf in the current directory for settings. But it will also read ~/.sqitch/sqitch.conf for user-specific settings. Since Vertica's "vsql" client is not in the path on my system, let's go ahead an tell it where to find the client on our computer:

  > sqitch config --user engine.vertica.client /opt/vertica/bin/vsql

And let's also tell it who we are, since this data will be used in all of our projects:

  > sqitch config --user user.name 'Marge N. OXVera'
  > sqitch config --user user.email 'marge@example.com'

Have a look at ~/.sqitch/sqitch.conf and you'll see this:

  > cat ~/.sqitch/sqitch.conf
  [engine "vertica"]
        client = /opt/vertica/bin/vsql
  [user]
        name = Marge N. OXVera
        email = marge@example.com

Which means that Sqitch should be able to find "vsql" for any project, and that it will always properly identify us when planning and committing changes.

Back to the repository. Have a look at the plan file, sqitch.plan:

  > cat sqitch.plan
  %syntax-version=1.0.0
  %project=flipr
  %uri=https://github.com/theory/sqitch-vertica-intro/

Note that it has picked up on the name and URI of the app we're building. Sqitch uses this data to manage cross-project dependencies. The "%syntax-version" pragma is always set by Sqitch, so that it always knows how to parse the plan, even if the format changes in the future.

Let's commit these changes and start creating the database changes.

  > git add .
  > git commit -am 'Initialize Sqitch configuration.'
  [master a42564d] Initialize Sqitch configuration.
   2 files changed, 16 insertions(+), 0 deletions(-)
   create mode 100644 sqitch.conf
   create mode 100644 sqitch.plan

Our First Change

First, our project will need a schema. This creates a nice namespace for all of the objects that will be part of the flipr app. Run this command:

  > sqitch add appschema -n 'Add schema for all flipr objects.'
  Created deploy/appschema.sql
  Created revert/appschema.sql
  Created verify/appschema.sql
  Added "appschema" to sqitch.plan

The "add" command adds a database change to the plan and writes deploy, revert, and verify scripts that represent the change. Now we edit these files. The "deploy" script's job is to create the schema. So we add this to deploy/appschema.sql:

  CREATE SCHEMA flipr;

The "revert" script's job is to precisely revert the change to the deploy script, so we add this to revert/appschema.sql:

  DROP SCHEMA flipr;

Now we can try deploying this change. We tell Sqitch where to send the change via a database URI <https://github.com/theory/uri-db/>, assuming the default "dbadmin" database and user and an ODBC driver named "Vertica" (see "Connection Configuration" for details):

  > sqitch deploy db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica
  Adding registry tables to db:vertica://dbadmin:@localhost:5433/dbadmin?Driver=Vertica
  Deploying changes to db:vertica://dbadmin:@localhost:5433/dbadmin?Driver=Vertica
    + appschema .. ok

First Sqitch created registry tables used to track database changes. The structure and name of the registry varies between databases (Vertica uses a schema to namespace its registry, while SQLite and MySQL use separate databases). Next, Sqitch deploys changes. We only have one so far; the "+" reinforces the idea that the change is being "added" to the database.

With this change deployed, if you connect to the database, you'll be able to see the schema:

  > vsql -U dbadmin -c '\dn flipr'
        List of schemas
   Name  |  Owner  | Comment 
  -------+---------+---------
   flipr | dbadmin |

Trust, But Verify

But that's too much work. Do you really want to do something like that after every deploy?

Here's where the "verify" script comes in. Its job is to test that the deploy did was it was supposed to. It should do so without regard to any data that might be in the database, and should throw an error if the deploy was not successful. In Vertica, the simplest way to do so for schema is probably to simply create an object in the schema. Put this SQL into verify/appschema.sql:

  CREATE TABLE flipr.verify__ (id int);
  DROP   TABLE flipr.verify__;

In truth, you can use any query that generates an SQL error if the schema doesn't exist. Another handy way to do that is to divide by zero if an object doesn't exist. For example, to throw an error when the "flipr" schema does not exist, you could do something like this:

  SELECT 1/COUNT(*) FROM v_catalog.schemata WHERE schema_name = 'flipr';

Either way, run the "verify" script with the "verify" command:

  > sqitch verify db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica
  Verifying db:vertica://dbadmin:@localhost:5433/dbadmin?Driver=Vertica
    * appschema .. ok
  Verify successful

Looks good! If you want to make sure that the verify script correctly dies if the schema doesn't exist, temporarily change the schema name in the script to something that doesn't exist, something like:

  CREATE TABLE nonesuch.verify__ (id int);

Then "verify" again:

  > sqitch verify db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica
  Verifying db:vertica://dbadmin:@localhost:5433/dbadmin?Driver=Vertica
    * appschema .. vsql:verify/appschema.sql:5: ROLLBACK 4650:  Schema "nonesuch" does not exist
  # Verify script "verify/appschema.sql" failed.
  not ok

  Verify Summary Report
  ---------------------
  Changes: 1
  Errors:  1
  Verify failed

It's even nice enough to tell us what the problem is. Or, for the divide-by-zero example, change the schema name:

  SELECT 1/COUNT(*) FROM v_catalog.schemata WHERE schema_name = 'nonesuch';

Then the verify will look something like:

  > sqitch verify db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica
  Verifying db:vertica://dbadmin:@localhost:5433/dbadmin?Driver=Vertica
    * appschema .. vsql:verify/appschema.sql:5: ERROR 2005:  division by zero
  # Verify script "verify/appschema.sql" failed.
  not ok

  Verify Summary Report
  ---------------------
  Changes: 1
  Errors:  1
  Verify failed

Less useful error output, but enough to alert us that something has gone wrong.

Don't forget to change the schema name back before continuing!

Status, Revert, Log, Repeat

For purely informational purposes, we can always see how a deployment was recorded via the "status" command, which reads the registry tables from the database:

  > sqitch status db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica
  # On database db:vertica://dbadmin:@localhost:5433/dbadmin?Driver=Vertica
  # Project:  flipr
  # Change:   f9759f0ed77964b6a3b6c7aa3b6058b4bb7db764
  # Name:     appschema
  # Deployed: 2014-09-04 15:26:28 -0700
  # By:       Marge N. OXVera <marge@example.com>
  # 
  Nothing to deploy (up-to-date)

Let's make sure that we can revert the change:

  > sqitch revert db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica
  Revert all changes from db:vertica://dbadmin:@localhost:5433/dbadmin?Driver=Vertica? [Yes] 
    - appschema .. ok

The "revert" command first prompts to make sure that we really do want to revert. This is to prevent unnecessary accidents. You can pass the "-y" option to disable the prompt. Also, notice the "-" before the change name in the output, which reinforces that the change is being removed from the database. And now the schema should be gone:

  > vsql -U dbadmin -c '\dn flipr'
      List of schemas
   Name | Owner | Comment 
  ------+-------+---------
  (0 rows)

And the status message should reflect as much:

  > sqitch status db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica
  # On database db:vertica://dbadmin:@localhost:5433/dbadmin?Driver=Vertica
  No changes deployed

Of course, since nothing is deployed, the "verify" command has nothing to verify:

  > sqitch verify db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica
  Verifying db:vertica://dbadmin:@localhost:5433/dbadmin?Driver=Vertica
  No changes deployed

However, we still have a record that the change happened, visible via the "log" command:

  > sqitch log db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica
  On database db:vertica://dbadmin:@localhost:5433/dbadmin?Driver=Vertica
  Revert f9759f0ed77964b6a3b6c7aa3b6058b4bb7db764
  Name:      appschema
  Committer: Marge N. OXVera <marge@example.com>
  Date:      2014-09-04 16:33:02 -0700

      Add schema for all flipr objects.

  Deploy f9759f0ed77964b6a3b6c7aa3b6058b4bb7db764
  Name:      appschema
  Committer: Marge N. OXVera <marge@example.com>
  Date:      2014-09-04 15:26:28 -0700

      Add schema for all flipr objects.

Note that the actions we took are shown in reverse chronological order, with the revert first and then the deploy.

Cool. Now let's commit it.

  > git add .
  > git commit -m 'Add flipr schema.'
  [master 9bee4bd] Add flipr schema.
   5 files changed, 197 insertions(+), 0 deletions(-)
   create mode 100644 deploy/appschema.sql
   create mode 100644 revert/appschema.sql
   create mode 100644 sqitch.sql
   create mode 100644 verify/appschema.sql

And then deploy again. This time, let's use the "--verify" option, so that the "verify" script is applied when the change is deployed:

  > sqitch deploy --verify db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica
  Deploying changes to db:vertica://dbadmin:@localhost:5433/dbadmin?Driver=Vertica
    + appschema .. ok

And now the schema should be back:

  > vsql -U dbadmin -c '\dn flipr'
        List of schemas
   Name  |  Owner  | Comment 
  -------+---------+---------
   flipr | dbadmin |

When we look at the status, the deployment will be there:

  > sqitch status db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica
  # On database db:vertica://dbadmin:@localhost:5433/dbadmin?Driver=Vertica
  # Project:  flipr
  # Change:   f9759f0ed77964b6a3b6c7aa3b6058b4bb7db764
  # Name:     appschema
  # Deployed: 2014-09-04 16:37:38 -0700
  # By:       Marge N. OXVera <marge@example.com>
  # 
  Nothing to deploy (up-to-date)

On Target

I'm getting a little tired of always having to type "db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica", aren't you? This database connection URI <https://github.com/theory/uri-db/> tells Sqitch how to connect to the deployment target, but we don't have to keep using the URI. We can name the target:

  > sqitch target add flipr_test db:vertica://dbadmin:password@localhost:5433/dbadmin?Driver=Vertica

The "target" command, inspired by "git-remote" <http://git-scm.com/docs/git-remote>, allows management of one or more named deployment targets. We've just added a target named "flipr_test", which means we can use the string "flipr_test" for the target, rather than the URI. But since we're doing so much testing, we can also tell Sqitch to deploy to the "flipr_test" target by default:

  > sqitch engine add vertica flipr_test

Now we can omit the target argument altogether, unless we need to deploy to another database. Which we will, eventually, but at least our examples will be simpler from here on in, e.g.:

  > sqitch status
  # On database flipr_test
  # Project:  flipr
  # Change:   f9759f0ed77964b6a3b6c7aa3b6058b4bb7db764
  # Name:     appschema
  # Deployed: 2014-09-04 16:37:38 -0700
  # By:       Marge N. OXVera <marge@example.com>
  # 
  Nothing to deploy (up-to-date)

Yay, that allows things to be a little more concise. Let's also make sure that changes are verified after deploying them:

  > sqitch config --bool deploy.verify true
  > sqitch config --bool rebase.verify true

We'll see the "rebase" command a bit later. In the meantime, let's commit the new configuration and and make some more changes!

  > git commit -am 'Set default deployment target and always verify.'     
  [master 469779a] Set default deployment target and always verify.
   1 files changed, 8 insertions(+), 0 deletions(-)

Deploy with Dependency

Let's add another change, this time to create a table. Our app will need users, of course, so we'll create a table for them. First, add the new change:

  > sqitch add users --requires appschema -n 'Creates table to track our users.'
  Created deploy/users.sql
  Created revert/users.sql
  Created verify/users.sql
  Added "users [appschema]" to sqitch.plan

Note that we're requiring the "appschema" change as a dependency of the new "users" change. Although that change has already been added to the plan and therefore should always be applied before the "users" change, it's a good idea to be explicit about dependencies.

Now edit the scripts. When you're done, deploy/users.sql should look like this:

  -- Deploy flipr:users                                                                                  to vertica
  -- requires: appschema                                                                          

  CREATE TABLE flipr.users (
      nickname  VARCHAR      PRIMARY KEY,
      password  VARCHAR      NOT NULL,
      fullname  VARCHAR(256) NOT NULL,
      twitter   VARCHAR      NOT NULL,
      timestamp TIMESTAMPTZ  NOT NULL DEFAULT NOW()
  );

A few things to notice here. On the second line, the dependence on the "appschema" change has been listed. This doesn't do anything, but the default "deploy" Vertica template lists it here for your reference while editing the file. Useful, right?

The table itself will be created in the "flipr" schema. This is why we need to require the "appschema" change.

Now for the verify script. The simplest way to check that the table was created and has the expected columns without touching the data? Just select from the table with a false "WHERE" clause. Add this to verify/users.sql:

  SELECT nickname, password, twitter, timestamp
    FROM flipr.users
   WHERE FALSE;

Now for the revert script: all we have to do is drop the table. Add this to revert/users.sql:

  DROP TABLE flipr.users;

Couldn't be much simpler, right? Let's deploy this bad boy:

  > sqitch deploy
  Deploying changes to flipr_test
    + users .. ok

We know, since verification is enabled, that the table must have been created. But for the purposes of visibility, let's have a quick look:

  > vsql -U dbadmin -c '\d flipr.users'
                                        List of Fields by Tables
   Schema | Table |   Column    |    Type     | Size | Default | Not Null | Primary Key | Foreign Key 
  --------+-------+-------------+-------------+------+---------+----------+-------------+-------------
   flipr  | users | nickname    | varchar(80) |   80 |         | t        | t           | 
   flipr  | users | password    | varchar(80) |   80 |         | t        | f           | 
   flipr  | users | "timestamp" | timestamptz |    8 | now()   | t        | f           |

We can also verify all currently deployed changes with the "verify" command:

  > sqitch verify
  Verifying flipr_test
    * appschema .. ok
    * users ...... ok
  Verify successful

Now have a look at the status:

  > sqitch status
  # On database flipr_test
  # Project:  flipr
  # Change:   d647ac8c130a7e0b12c9049789e46afb4a4f6e53
  # Name:     users
  # Deployed: 2014-09-04 16:42:45 -0700
  # By:       Marge N. OXVera <marge@example.com>
  # 
  Nothing to deploy (up-to-date)

Success! Let's make sure we can revert the change, as well:

  > sqitch revert --to @HEAD^ -y
  Reverting changes to appschema from flipr_test
    - users .. ok

Note that we've used the "--to" option to specify the change to revert to. And what do we revert to? The symbolic tag @HEAD, when passed to "revert", always refers to the last change deployed to the database. (For other commands, it refers to the last change in the plan.) Appending the caret ("^") tells Sqitch to select the change prior to the last deployed change. So we revert to "appschema", the penultimate change. The other potentially useful symbolic tag is @ROOT, which refers to the first change deployed to the database (or in the plan, depending on the command).

Back to the database. The "users" table should be gone but the "flipr" schema should still be around:

  > vsql -U dbadmin -c '\d flipr.users'
  Did not find any relation.

The "status" command politely informs us that we have undeployed changes:

  > sqitch status
  # On database flipr_test
  # Project:  flipr
  # Change:   f9759f0ed77964b6a3b6c7aa3b6058b4bb7db764
  # Name:     appschema
  # Deployed: 2014-09-04 16:37:38 -0700
  # By:       Marge N. OXVera <marge@example.com>
  # 
  Undeployed change:
    * users

As does the "verify" command:

  > sqitch verify
  Verifying flipr_test
    * appschema .. ok
  Undeployed change:
    * users
  Verify successful

Note that the verify is successful, because all currently-deployed changes are verified. The list of undeployed changes (just "users" here) reminds us about the current state.

Okay, let's commit and deploy again:

  > git add .
  > git commit -am 'Add users table.'
  [master c7c24c5] Add users table.
   4 files changed, 18 insertions(+), 0 deletions(-)
   create mode 100644 deploy/users.sql
   create mode 100644 revert/users.sql
   create mode 100644 verify/users.sql
  Deploying changes to flipr_test
    + users .. ok

Looks good. Check the status:

  > sqitch status
  # On database flipr_test
  # Project:  flipr
  # Change:   d647ac8c130a7e0b12c9049789e46afb4a4f6e53
  # Name:     users
  # Deployed: 2014-09-04 17:42:53 -0700
  # By:       Marge N. OXVera <marge@example.com>
  # 
  Nothing to deploy (up-to-date)

Excellent. Let's do some more!

Add Two at Once

Let's add a couple more changes. Our app will need to store status messages from users. Let's call them -- and the table to store them -- "flips". And we'll also need a view that lists user names with their flips. Let's add changes for them both:

  > sqitch add flips -r appschema -r users -n 'Adds table for storing flips.'
  Created deploy/flips.sql
  Created revert/flips.sql
  Created verify/flips.sql
  Added "flips [appschema users]" to sqitch.plan

  > sqitch add userflips -r appschema -r users -r flips \
        -n 'Creates the userflips view.'
  Created deploy/userflips.sql
  Created revert/userflips.sql
  Created verify/userflips.sql
  Added "userflips [appschema users flips]" to sqitch.plan

Now might be a good time to have a look at the deployment plan:

  > cat sqitch.plan
  %syntax-version=1.0.0
  %project=flipr
  %uri=https://github.com/theory/sqitch-vertica-intro/

  appschema 2014-09-04T18:40:34Z Marge N. OXVera <marge@example.com> # Add schema for all flipr objects.
  users [appschema] 2014-09-04T23:40:15Z Marge N. OXVera <marge@example.com> # Creates table to track our users.
  flips [appschema users] 2014-09-05T00:16:58Z Marge N. OXVera <marge@example.com> # Adds table for storing flips.
  userflips [appschema users flips] 2014-09-05T00:18:43Z Marge N. OXVera <marge@example.com> # Creates the userflips view.

Each change appears on a single line with the name of the change, a bracketed list of dependencies, a timestamp, the name and email address of the user who planned the change, and a note.

Let's write the code for the new changes. Here's what deploy/flips.sql should look like:

  -- Deploy flipr:flips to vertica
  -- requires: appschema
  -- requires: users
  
  CREATE TABLE flipr.flips (
      id        AUTO_INCREMENT PRIMARY KEY ,
      nickname  VARCHAR        NOT NULL REFERENCES flipr.users(nickname),
      body      VARCHAR(180)   NOT NULL DEFAULT '',
      timestamp TIMESTAMPTZ    NOT NULL DEFAULT clock_timestamp()
  );

Here's what verify/flips.sql might look like:

  -- Verify flipr:flips                                                                                  on vertica
  SELECT id, nickname, body, timestamp
    FROM flipr.flips
   WHERE FALSE;

We simply take advantage of the fact that "has_function_privilege()" throws an exception if the specified function does not exist.

And revert/flips.sql should look something like this:

  -- Revert flipr:flips from vertica
  DROP TABLE flipr.flips;

Now for "userflips"; deploy/userflips.sql might look like this:

  -- Deploy flipr:userflips to vertica
  -- requires: appschema
  -- requires: users
  -- requires: flips

  CREATE OR REPLACE VIEW flipr.userflips AS
  SELECT f.id, u.nickname, u.fullname, f.body, f.timestamp
    FROM flipr.users u
    JOIN flipr.flips f ON u.nickname = f.nickname;

Use a "SELECT" statement in verify/userflips.sql again:

  -- Verify flipr:userflips on vertica
  SELECT id, nickname, fullname, body, timestamp
    FROM flipr.userflips
   WHERE FALSE;

And of course, its "revert" script, revert/userflips.sql, should look something like:

  -- Revert flipr:userflips from vertica
  DROP VIEW flipr.userflips;

Try em out!

  > sqitch deploy
  Deploying changes to flipr_test
    + flips ...... ok
    + userflips .. ok

Do we have the new table and view? Of course we do, they were verified. Still, have a look:

  > vsql -U dbadmin -c '\dt flipr.flips'
                 List of tables
   Schema | Name  | Kind  |  Owner  | Comment 
  --------+-------+-------+---------+---------
   flipr  | flips | table | dbadmin | 

  > vsql -U dbadmin -c '\dv flipr.userflips'
                    List of View Fields
   Schema |   View    |   Column    |     Type     | Size 
  --------+-----------+-------------+--------------+------
   flipr  | userflips | id          | int          |    8
   flipr  | userflips | nickname    | varchar(80)  |   80
   flipr  | userflips | fullname    | varchar(256) |  256
   flipr  | userflips | body        | varchar(180) |  180
   flipr  | userflips | "timestamp" | timestamptz  |    8

And what's the status?

  > sqitch status 
  # On database flipr_test
  # Project:  flipr
  # Change:   d1f998618fb863d93049a724fd0d2b49a29add86
  # Name:     userflips
  # Deployed: 2014-09-04 17:51:21 -0700
  # By:       Marge N. OXVera <marge@example.com>
  # 
  Nothing to deploy (up-to-date)

Looks good. Let's make sure revert works:

  > sqitch revert -y --to @HEAD^
  Reverting changes to users from flipr_test
    - userflips .. ok
    - flips ...... ok
  >  vsql -U dbadmin -c '\d flipr.flips'
  Did not find any relation.
  > vsql -U dbadmin -c '\dv flipr.userflips'
  No matching relations found.

Note the use of "@HEAD^^" to specify that the revert be to two changes prior the last deployed change. Looks good. Let's do the commit and re-deploy dance:

  > git add .
  > git commit -m 'Add flips table and userflips view.'
  [master c40f23f] Add flips table and userflips view.
   7 files changed, 41 insertions(+), 0 deletions(-)
   create mode 100644 deploy/flips.sql
   create mode 100644 deploy/userflips.sql
   create mode 100644 revert/flips.sql
   create mode 100644 revert/userflips.sql
   create mode 100644 verify/flips.sql
   create mode 100644 verify/userflips.sql
 
  > sqitch deploy
  Deploying changes to flipr_test
    + flips ...... ok
    + userflips .. ok

  > sqitch status
  # On database flipr_test
  # Project:  flipr
  # Change:   d1f998618fb863d93049a724fd0d2b49a29add86
  # Name:     userflips
  # Deployed: 2014-09-04 17:59:34 -0700
  # By:       Marge N. OXVera <marge@example.com>
  # 
  Nothing to deploy (up-to-date)
  
  > sqitch verify
  Verifying flipr_test
    * appschema .. ok
    * users ...... ok
    * flips ...... ok
    * userflips .. ok
  Verify successful

Great, we're fully up-to-date!

Ship It!

Let's do a first release of our app. Let's call it "1.0.0-dev1" Since we want to have it go out with deployments tied to the release, let's tag it:

  > sqitch tag v1.0.0-dev1 -n 'Tag v1.0.0-dev1.'
  Tagged "userflips" with @v1.0.0-dev1
  > git commit -am 'Tag the database with v1.0.0-dev1.'
  [master b07ce3d] Tag the database with v1.0.0-dev1.
   1 files changed, 1 insertions(+), 0 deletions(-)
  > git tag v1.0.0-dev1 -am 'Tag v1.0.0-dev1'

We can try deploying to make sure the tag gets picked up like so:

  > sqitch deploy
  Nothing to deploy (up-to-date)
  > sqitch status
  # On database flipr_test
  # Project:  flipr
  # Change:   d1f998618fb863d93049a724fd0d2b49a29add86
  # Name:     userflips
  # Tag:      @v1.0.0-dev1
  # Deployed: 2014-09-04 17:59:34 -0700
  # By:       Marge N. OXVera <marge@example.com>
  # 
  Nothing to deploy (up-to-date)

Note the new "Tag" line in the output of "sqitch status": no new changes needed to be deployed, but Sqitch did deploy the tag on the "userflips" change. Now let's bundle everything up for release:

  > sqitch bundle
  Bundling into bundle
  Writing config
  Writing plan
  Writing scripts
    + appschema
    + users
    + flips
    + userflips @v1.0.0-dev1

Now we can package the bundle directory and distribute it. When it gets installed somewhere, users can use Sqitch to deploy to the database. Let's try deploying it to another database:

  > cd bundle
  > sqitch deploy db:vertica://dbadmin:password@db.example.com:5433/flipr?Driver=Vertica
  Adding registry tables to db:vertica://dbadmin:@db.example.com:5433/flipr?Driver=Vertica
  Deploying changes to db:vertica://dbadmin:@db.example.com:5433/flipr?Driver=Vertica
    + appschema ............... ok
    + users ................... ok
    + flips ................... ok
    + userflips @v1.0.0-dev1 .. ok

Notice how the tag on "userflips" now appears in the deploy output. Nice, eh? Now, package it up and ship it!

Making a Hash of Things

Now that we've got the basics of the app done, let's add a feature. Gotta track the hashtags associated with flips, right? Let's add a table for them. But since other folks are working on other tasks in the repository, we'll work on a branch, so we can all stay out of each other's way. So let's branch:

Making a Hash of Things

  > git checkout -b hashtags
  Switched to a new branch 'hashtags'

Now we can add a new change to create a table for hashtags.

  > sqitch add hashtags --requires flips -n 'Adds table for storing hashtags.'
  Created deploy/hashtags.sql
  Created revert/hashtags.sql
  Created verify/hashtags.sql
  Added "hashtags [appschema flips]" to sqitch.plan

You know the drill by now. Add this to deploy/hashtags.sql

  CREATE TABLE flipr.hashtags (
      flip_id   BIGINT  NOT   NULL REFERENCES flipr.Flips(id),
      hashtag   VARCHAR(128)  NOT NULL,
      PRIMARY KEY (flip_id, hashtag)
  );

Again, select from the table in verify/hashtags.sql:

  SELECT flip_id, hashtag FROM flipr.hashtags WHERE FALSE;

And drop it in revert/hashtags.sql

  DROP TABLE flipr.hashtags;

And give it a whirl:

  > sqitch deploy
  Deploying changes to flipr_test
        + hashtags .. ok

Look good?

  > sqitch status --show-tags
  # On database flipr_test
  # Project:  flipr
  # Change:   fda6daef73e0ac12252bf6af5f259ccb207d4197
  # Name:     hashtags
  # Deployed: 2014-09-05 10:46:20 -0700
  # By:       Marge N. OXVera <marge@example.com>
  # 
  # Tag:
  #   @v1.0.0-dev1 - 2014-09-05 09:09:38 -0700 - Marge N. OXVera <marge@example.com>
  # 
  Nothing to deploy (up-to-date)

Note the use of "--show tags" to show all the deployed tags. Make sure we can revert, too:

  > sqitch rebase -y --onto @HEAD^
  Reverting changes to userflips @v1.0.0-dev1 from flipr_test
    - hashtags .. ok
  Deploying changes to flipr_test
    + hashtags .. ok

Great! Now make it so:

  > git add .
  > git commit -m 'Add hashtags table.'
  [hashtags d893e9c] Add hashtags table.
   4 files changed, 18 insertions(+), 0 deletions(-)
   create mode 100644 deploy/hashtags.sql
   create mode 100644 revert/hashtags.sql
   create mode 100644 verify/hashtags.sql

Good, we've finished this feature. Time to merge back into "master".

Emergency

Let's do it:

  > git checkout master
  Switched to branch 'master'
  > git pull
  Updating b07ce3d..05d3e5d
  Fast-forward
   deploy/lists.sql |   10 ++++++++++
   revert/lists.sql |    3 +++
   sqitch.plan      |    2 ++
   verify/lists.sql |    5 +++++
   4 files changed, 20 insertions(+), 0 deletions(-)
   create mode 100644 deploy/lists.sql
   create mode 100644 revert/lists.sql
   create mode 100644 verify/lists.sql

Hrm, that's interesting. Looks like someone made some changes to "master". They added list support. Well, let's see what happens when we merge our changes.

  > git merge --no-ff hashtags
  Auto-merging sqitch.plan
  CONFLICT (content): Merge conflict in sqitch.plan
  Automatic merge failed; fix conflicts and then commit the result.

Oh, a conflict in sqitch.plan. Not too surprising, since both the merged "lists" branch and our "hashtags" branch added changes to the plan. Let's try a different approach.

The truth is, we got lazy. Those changes when we pulled master from the origin should have raised a red flag. It's considered a bad practice not to look at what's changed in "master" before merging in a branch. What one should do is either:

Rebase the hashtags branch from master before merging. This "rewinds" the branch changes, pulls from "master", and then replays the changes back on top of the pulled changes.
Create a patch and apply that to master. This is the sort of thing you might have to do if you're sending changes to another user, especially if the VCS is not Git.

So let's restore things to how they were at master:

  > git reset --hard HEAD
  HEAD is now at 05d3e5d Merge branch 'lists'

That throws out our botched merge. Now let's go back to our branch and rebase it on "master":

  > git checkout hashtags
  Switched to branch 'hashtags'
  > git rebase master
  First, rewinding head to replay your work on top of it...
  Applying: Add hashtags table.
  Using index info to reconstruct a base tree...
  <stdin>:16: new blank line at EOF.
  +
  warning: 1 line adds whitespace errors.
  Falling back to patching base and 3-way merge...
  Auto-merging sqitch.plan
  CONFLICT (content): Merge conflict in sqitch.plan
  Failed to merge in the changes.
  Patch failed at 0001 Add hashtags table.

  When you have resolved this problem run "git rebase --continue".
  If you would prefer to skip this patch, instead run "git rebase --skip".
  To restore the original branch and stop rebasing run "git rebase --abort".

Oy, that's kind of a pain. It seems like no matter what we do, we'll need to resolve conflicts in that file. Except in Git. Fortunately for us, we can tell Git to resolve conflicts in sqitch.plan differently. Because we only ever append lines to the file, we can have it use the "union" merge driver, which, according to its docs <http://git-scm.com/docs/gitattributes#_built-in_merge_drivers>:

Run 3-way file level merge for text files, but take lines from both versions, instead of leaving conflict markers. This tends to leave the added lines in the resulting file in random order and the user should verify the result. Do not use this if you do not understand the implications.

This has the effect of appending lines from all the merging files, which is exactly what we need. So let's give it a try. First, back out the botched rebase:

  > git rebase --abort
  HEAD is now at d893e9c Add hashtags table.

Now add the union merge driver to .gitattributes for sqitch.plan and rebase again:

  > echo sqitch.plan merge=union > .gitattributes
  > git rebase master
  First, rewinding head to replay your work on top of it...
  Applying: Add hashtags table.
  Using index info to reconstruct a base tree...
  <stdin>:16: new blank line at EOF.
  +
  warning: 1 line adds whitespace errors.
  Falling back to patching base and 3-way merge...
  Auto-merging sqitch.plan

Ah, that looks a bit better. Let's have a look at the plan:

  > cat sqitch.plan
  %syntax-version=1.0.0
  %project=flipr
  %uri=https://github.com/theory/sqitch-vertica-intro/

  appschema 2014-09-04T18:40:34Z Marge N. OXVera <marge@example.com> # Add schema for all flipr objects.
  users [appschema] 2014-09-04T23:40:15Z Marge N. OXVera <marge@example.com> # Creates table to track our users.
  flips [appschema users] 2014-09-05T00:16:58Z Marge N. OXVera <marge@example.com> # Adds table for storing flips.
  userflips [appschema users flips] 2014-09-05T00:18:43Z Marge N. OXVera <marge@example.com> # Creates the userflips view.
  @v1.0.0-dev1 2014-09-05T16:04:48Z Marge N. OXVera <marge@example.com> # Tag v1.0.0-dev1.

  lists [appschema users] 2014-09-05T17:33:43Z Marge N. OXVera <marge@example.com> # Adds table for storing lists.
  hashtags [appschema flips] 2014-09-05T17:39:53Z Marge N. OXVera <marge@example.com> # Adds table for storing hashtags.

Note that it has appended the changes from the merged "lists" branch, and then merged the changes from our "hashtags" branch. Test it to make sure it works as expected:

  > sqitch rebase -y
  Reverting all changes from flipr_test
    - hashtags ................ ok
    - userflips @v1.0.0-dev1 .. ok
    - flips ................... ok
    - users ................... ok
    - appschema ............... ok
  Deploying changes to flipr_test
    + appschema ............... ok
    + users ................... ok
    + flips ................... ok
    + userflips @v1.0.0-dev1 .. ok
    + lists ................... ok
    + hashtags ................ ok

Note the use of "rebase", which combines a "revert" and a "deploy" into a single command. Handy, right? It correctly reverted our changes, and then deployed them all again in the proper order. So let's commit .gitattributes; seems worthwhile to keep that change:

  > git add .
  > git commit -m 'Add `.gitattributes` with union merge for `sqitch.plan`.'
  [hashtags 2f065a3] Add `.gitattributes` with union merge for `sqitch.plan`.
   1 files changed, 1 insertions(+), 0 deletions(-)
   create mode 100644 .gitattributes

Merges Mastered

And now, finally, we can merge into "master":

  > git checkout master
  Switched to branch 'master'
  > git merge --no-ff hashtags -m "Merge branch 'hashtags'"
  Merge made by recursive.
   .gitattributes      |    1 +
   deploy/hashtags.sql |   10 ++++++++++
   revert/hashtags.sql |    3 +++
   sqitch.plan         |    1 +
   verify/hashtags.sql |    3 +++
   5 files changed, 18 insertions(+), 0 deletions(-)
   create mode 100644 .gitattributes
   create mode 100644 deploy/hashtags.sql
   create mode 100644 revert/hashtags.sql
   create mode 100644 verify/hashtags.sql

And double-check our work:

  > cat sqitch.plan
  %syntax-version=1.0.0
  %project=flipr
  %uri=https://github.com/theory/sqitch-vertica-intro/

  appschema 2014-09-04T18:40:34Z Marge N. OXVera <marge@example.com> # Add schema for all flipr objects.
  users [appschema] 2014-09-04T23:40:15Z Marge N. OXVera <marge@example.com> # Creates table to track our users.
  flips [appschema users] 2014-09-05T00:16:58Z Marge N. OXVera <marge@example.com> # Adds table for storing flips.
  userflips [appschema users flips] 2014-09-05T00:18:43Z Marge N. OXVera <marge@example.com> # Creates the userflips view.
  @v1.0.0-dev1 2014-09-05T16:04:48Z Marge N. OXVera <marge@example.com> # Tag v1.0.0-dev1.

  lists [appschema users] 2014-09-05T17:33:43Z Marge N. OXVera <marge@example.com> # Adds table for storing lists.
  hashtags [appschema flips] 2014-09-05T17:39:53Z Marge N. OXVera <marge@example.com> # Adds table for storing hashtags.

Much much better, a nice clean master now. And because it is now identical to the "hashtags" branch, we can just carry on. Go ahead and tag it, bundle, and release:

  > sqitch tag v1.0.0-dev2 -n 'Tag v1.0.0-dev2.'
  Tagged "hashtags" with @v1.0.0-dev2
  > git commit -am 'Tag the database with v1.0.0-dev2.'
  [master 8a6a73b] Tag the database with v1.0.0-dev2.
   1 files changed, 1 insertions(+), 0 deletions(-)
  > git tag v1.0.0-dev2 -am 'Tag v1.0.0-dev2'
  > sqitch bundle --dest-dir flipr-1.0.0-dev2
  Bundling into flipr-1.0.0-dev2
  Writing config
  Writing plan
  Writing scripts
    + appschema
    + users
    + flips
    + userflips @v1.0.0-dev1
    + lists
    + hashtags @v1.0.0-dev2

Note the use of the "--dest-dir" option to "sqitch bundle". Just a nicer way to create the top-level directory name so we don't have to rename it from bundle.

In Place Changes

Well, some folks have been testing the "1.0.0-dev2" release and have demanded that Twitter user links be added to Flipr pages. Why anyone would want to include social network links in an anti-social networking app is beyond us programmers, but we're just the plumbers, right? Gotta go with what Product demands. The upshot is that we need to update the "userflips" view, which is used for the feature in question, to include the Twitter user names.

Normally, modifying views in database changes is a PITA <http://www.urbandictionary.com/define.php?term=pita>. You have to make changes like these:

1.: Copy deploy/userflips.sql to deploy/userflips_twitter.sql.
2.: Edit deploy/userflips_twitter.sql to drop and re-create the view with the "twitter" column to the view.
3.: Copy deploy/userflips.sql to revert/userflips_twitter.sql. Yes, copy the original change script to the new revert change.
4.: Add a "DROP VIEW" statement to revert/userflips_twitter.sql.
5.: Copy verify/userflips.sql to verify/userflips_twitter.sql.
6.: Modify verify/userflips_twitter.sql to include a check for the "twiter" column.
7.: Test the changes to make sure you can deploy and revert the "userflips_twitter" change.

But you can have Sqitch do most of the work for you. The only requirement is that a tag appear between the two instances of a change we want to modify. In general, you're going to make a change like this after a release, which you've tagged anyway, right? Well we have, with "@v1.0.0-dev2" added in the previous section. With that, we can let Sqitch do most of the hard work for us, thanks to the "rework" command, which is similar to "add":

  > sqitch rework userflips -n 'Adds userflips.twitter.'
  Added "userflips [userflips@v1.0.0-dev2]" to sqitch.plan.
  Modify these files as appropriate:
        * deploy/userflips.sql
        * revert/userflips.sql
        * verify/userflips.sql

Oh, so we can edit those files in place. Nice! How does Sqitch do it? Well, in point of fact, it has copied the files to stand in for the previous instance of the "userflips" change, which we can see via "git status":

  > git status
  # On branch master
  # Changed but not updated:
  #   (use "git add <file>..." to update what will be committed)
  #   (use "git checkout -- <file>..." to discard changes in working directory)
  #
  #     modified:   revert/userflips.sql
  #     modified:   sqitch.plan
  #
  # Untracked files:
  #   (use "git add <file>..." to include in what will be committed)
  #
  #     deploy/userflips@v1.0.0-dev2.sql
  #     revert/userflips@v1.0.0-dev2.sql
  #     verify/userflips@v1.0.0-dev2.sql
  no changes added to commit (use "git add" and/or "git commit -a")

The "untracked files" part of the output is the first thing to notice. They're all named "userflips@v1.0.0-dev2.sql". What that means is: "the "userflips" change as it was implemented as of the "@v1.0.0-dev2" tag." These are copies of the original scripts, and thereafter Sqitch will find them when it needs to run scripts for the first instance of the "userflips" change. As such, it's important not to change them again. But hey, if you're reworking the change, you shouldn't need to.

The other thing to notice is that revert/userflips.sql has changed. Sqitch replaced it with the original deploy script. As of now, deploy/userflips.sql and revert/userflips.sql are identical. This is on the assumption that the deploy script will be changed (we're reworking it, remember?), and that the revert script should actually change things back to how they were before. Of course, the original deploy script may not be idempotent <http://en.wikipedia.org/wiki/Idempotence> -- that is, able to be applied multiple times without changing the result beyond the initial application. If it's not, you will likely need to modify it so that it properly restores things to how they were after the original deploy script was deployed. Or, more simply, it should revert changes back to how they were as-of the deployment of deploy/userflips@v1.0.0-dev2.sql.

Fortunately, our function deploy scripts are already idempotent, thanks to the use of the "OR REPLACE" expression. No matter how many times a deployment script is run, the end result will be the same instance of the function, with no duplicates or errors.

As a result, there is no need to explicitly add changes. So go ahead. Modify the script to add the "twitter" column to the view. Make this change to deploy/userflips.sql:

  @@ -4,8 +4,9 @@
 
   BEGIN;
 
  @@ -4,6 +4,6 @@
   -- requires: flips
 
   CREATE OR REPLACE VIEW flipr.userflips AS
  -SELECT f.id, u.nickname, u.fullname, f.body, f.timestamp
  +SELECT f.id, u.nickname, u.fullname, u.twitter, f.body, f.timestamp
     FROM flipr.users u
     JOIN flipr.flips f ON u.nickname = f.nickname;

Next, modify verify/userflips.sql to check for the "twitter" column. Here's the diff:

  @@ -1,6 +1,6 @@
   -- Verify flipr:userflips on vertica
 
  -SELECT id, nickname, fullname, body, timestamp
  +SELECT id, nickname, fullname, twitter, body, timestamp
     FROM flipr.userflips
    WHERE FALSE;

Now try a deployment:

  > sqitch deploy
  Deploying changes to flipr_test
        + userflips .. ok

So, are the changes deployed?

  > vsql -U dbadmin -c '\dv flipr.userflips'
                    List of View Fields
   Schema |   View    |   Column    |     Type     | Size 
  --------+-----------+-------------+--------------+------
   flipr  | userflips | id          | int          |    8
   flipr  | userflips | nickname    | varchar(80)  |   80
   flipr  | userflips | fullname    | varchar(256) |  256
   flipr  | userflips | twitter     | varchar(80)  |   80
   flipr  | userflips | body        | varchar(180) |  180
   flipr  | userflips | "timestamp" | timestamptz  |    8

Awesome, the view now includes the "twitter" column. But can we revert?

  > sqitch revert --to @HEAD^ -y
  Reverting changes to hashtags @v1.0.0-dev2 from flipr_test
        - userflips .. ok

Did that work, is the "twitter" column gone?

  > vsql -U dbadmin -c '\dv flipr.userflips'
                    List of View Fields
   Schema |   View    |   Column    |     Type     | Size 
  --------+-----------+-------------+--------------+------
   flipr  | userflips | id          | int          |    8
   flipr  | userflips | nickname    | varchar(80)  |   80
   flipr  | userflips | fullname    | varchar(256) |  256
   flipr  | userflips | twitter     | varchar(80)  |   80
   flipr  | userflips | body        | varchar(180) |  180
   flipr  | userflips | "timestamp" | timestamptz  |    8

Yes, it works! Sqitch properly finds the original instances of these changes in the new script files that include tags.

Excellent. Let's go ahead and commit these changes:

  > git add .
  > git commit -m 'Add the twitter column to the userflips view.'
  [master 95d6dd0] Add the twitter column to the userflips view.
   7 files changed, 30 insertions(+), 4 deletions(-)
   create mode 100644 deploy/userflips@v1.0.0-dev2.sql
   create mode 100644 revert/userflips@v1.0.0-dev2.sql
   create mode 100644 verify/userflips@v1.0.0-dev2.sql

More to Come

Sqitch is a work in progress. Better integration with version control systems is planned to make managing idempotent reworkings even easier. Stay tuned.

Author

David E. Wheeler <david@justatheory.com>

License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.