add docs site (#102)

The current README is hard to navigate and discourages adding more examples. Having a documentation website should allow us to provide more detailed docs.

.eslintignore

@@ -1,3 +1,4 @@
 # don't ever lint node_modules
 node_modules
 .eslintrc.js
+docs

.prettierignore

@@ -6,3 +6,4 @@ coverage/
 .terraform/
 .pytest_cache/
 target/
+docs

docs/.gitignore

@@ -0,0 +1,20 @@
+# Dependencies
+/node_modules
+
+# Production
+/build
+
+# Generated files
+.docusaurus
+.cache-loader
+
+# Misc
+.DS_Store
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*

docs/README.md

@@ -0,0 +1,33 @@
+# Website
+
+This website is built using [Docusaurus 2](https://v2.docusaurus.io/), a modern static website generator.
+
+## Installation
+
+```console
+yarn install
+```
+
+## Local Development
+
+```console
+yarn start
+```
+
+This command starts a local development server and open up a browser window. Most changes are reflected live without having to restart the server.
+
+## Build
+
+```console
+yarn build
+```
+
+This command generates static content into the `build` directory and can be served using any static contents hosting service.
+
+## Deployment
+
+```console
+GIT_USER=<Your GitHub username> USE_SSH=true yarn deploy
+```
+
+If you are using GitHub pages for hosting, this command is a convenient way to build the website and push to the `gh-pages` branch.

docs/babel.config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  presets: [require.resolve('@docusaurus/core/lib/babel/preset')],
+};

docs/docs/adding-field-with-default.md

@@ -0,0 +1,39 @@
+---
+id: adding-field-with-default
+title: adding-field-with-default
+---
+
+:::note Postgres Version
+
+This lint only applies to Postgres versions less than 11.
+:::
+
+## problem
+
+On Postgres versions less than 11, adding a field with a `DEFAULT` requires a
+table rewrite with an `ACCESS EXCLUSIVE` lock.
+
+<https://www.postgresql.org/docs/10/sql-altertable.html#SQL-ALTERTABLE-NOTES>
+
+An `ACCESS EXCLUSIVE` lock blocks reads / writes while the statement is running.
+
+## solution
+
+Add the field as nullable, then set a default, backfill, and remove nullabilty.
+
+Instead of:
+
+```sql
+ALTER TABLE "core_recipe" ADD COLUMN "foo" integer DEFAULT 10 NOT NULL;
+```
+
+Use:
+
+```sql
+ALTER TABLE "core_recipe" ADD COLUMN "foo" integer;
+ALTER TABLE "core_recipe" ALTER COLUMN "foo" SET DEFAULT 10;
+-- backfill column in batches
+ALTER TABLE "core_recipe" ALTER COLUMN "foo" SET NOT NULL;
+```
+
+We add our column as nullable, set a default for new rows, backfill our column (ideally done in batches to limit locking), and finally remove nullability.

docs/docs/adding-foreign-key-constraint.md

@@ -0,0 +1,79 @@
+---
+id: adding-foreign-key-constraint
+title: adding-foreign-key-constraint
+---
+
+A foreign key constraint should be added with `NOT VALID`.
+
+Adding a foreign key constraint requires a table scan and a `SHARE ROW EXCLUSIVE` lock on both tables, which blocks writes.
+
+Adding the constraint as `NOT VALID` in one transaction and then using
+`VALIDATE` in another transaction will allow writes when adding the
+constraint.
+
+## problem
+
+Adding a foreign key constraint requires a table scan and a `SHARE ROW EXCLUSIVE` lock on both tables, which blocks writes to each table.
+
+This means no writes will be allowed to either table while the table you're altering is scanned to validate the constraint.
+
+## solution
+
+To prevent blocking writes to tables, add the constraint as `NOT VALID` in one transaction, then `VALIDATE CONSTRAINT` in another.
+
+While `NOT VALID` prevents row updates while running, it commits instantly if it can get a lock (see ["Safety requirements"](./safe_migrations.md#safety-requirements)). `VALIDATE CONSTRAINT` allows row updates while it scans
+the table.
+
+### adding constraint to existing table
+
+Instead of:
+
+```sql
+ALTER TABLE "email" ADD CONSTRAINT "fk_user"
+    FOREIGN KEY ("user_id") REFERENCES "user" ("id");
+```
+
+Use:
+
+```sql
+ALTER TABLE "email" ADD CONSTRAINT "fk_user"
+    FOREIGN KEY ("user_id") REFERENCES "user" ("id") NOT VALID;
+ALTER TABLE "email" VALIDATE CONSTRAINT "fk_user";
+```
+
+Add the foreign key constraint as `NOT VALID` to prevent locking the `"email"` and `"user"` tables.
+
+Run `VALIDATE CONSTRAINT` to scan the `"email"` table in the background while reads and writes continue.
+
+### adding constraint to new table
+
+Instead of:
+
+```sql
+CREATE TABLE email (
+    id BIGINT GENERATED ALWAYS AS IDENTITY,
+    user_id BIGINT,
+    email TEXT,
+    PRIMARY KEY(id),
+    CONSTRAINT fk_user
+        FOREIGN KEY ("user_id")
+        REFERENCES "user" ("id")
+);
+```
+
+Use:
+
+```sql
+CREATE TABLE email (
+    id BIGINT GENERATED ALWAYS AS IDENTITY,
+    user_id BIGINT,
+    email TEXT,
+    PRIMARY KEY(id)
+);
+
+ALTER TABLE "email" ADD CONSTRAINT "fk_user"
+    FOREIGN KEY ("user_id") REFERENCES "user" ("id") NOT VALID;
+ALTER TABLE "email" VALIDATE CONSTRAINT "fk_user";
+```
+
+Create the table, add the foreign key constraint as `NOT VALID`, then `VALIDATE` the constraint.

docs/docs/adding-not-nullable-field.md

@@ -0,0 +1,33 @@
+---
+id: adding-not-nullable-field
+title: adding-not-nullable-field
+---
+
+Use a check constraint instead of setting a column as `NOT NULL`.
+
+## problem
+
+Adding a column as `NOT NULL` requires a table scan and the `ALTER TABLE` requires
+an `ACCESS EXCLUSIVE` lock. Reads and writes will be disabled while this statement is running.
+
+## solution
+
+Add a column as nullable and use a check constraint to verify integrity. The check constraint should be added as `NOT NULL` and then validated.
+
+Instead of:
+
+```sql
+ALTER TABLE "core_recipe" ADD COLUMN "foo" integer DEFAULT 10 NOT NULL;
+```
+
+Use:
+
+```sql
+ALTER TABLE "core_recipe" ADD COLUMN "foo" integer DEFAULT 10;
+ALTER TABLE "core_recipe" ADD CONSTRAINT foo_not_null
+    CHECK ("foo" IS NOT NULL) NOT VALID;
+-- backfill column so it's not null
+ALTER TABLE "core_recipe" VALIDATE CONSTRAINT foo_not_null;
+```
+
+Add the column as nullable, add a check constraint as `NOT VALID` that verifies the column is not null, backfill the column so it no longer contains null values, validate the constraint to verify existing rows are valid.

docs/docs/adding-serial-primary-key-field.md

@@ -0,0 +1,25 @@
+---
+id: adding-serial-primary-key-field
+title: adding-serial-primary-key-field
+---
+
+Outlined in [Citus' 2018 post on tips for Postgres
+locking](https://www.citusdata.com/blog/2018/02/22/seven-tips-for-dealing-with-postgres-locks/)
+as well as [the Postgres docs](https://www.postgresql.org/docs/current/sql-altertable.html), adding a primary key constraint is a blocking
+operation.
+
+Instead of creating the constraint directly, consider creating the
+`CONSTRAINT` `USING` an index.
+
+From the Postgres docs:
+
+> To recreate a primary key constraint, without blocking updates while the
+> index is rebuilt:
+
+```sql
+CREATE UNIQUE INDEX CONCURRENTLY dist_id_temp_idx ON distributors (dist_id);
+ALTER TABLE distributors DROP CONSTRAINT distributors_pkey,
+    ADD CONSTRAINT distributors_pkey PRIMARY KEY USING INDEX dist_id_temp_idx;
+```
+
+<https://www.postgresql.org/docs/current/sql-altertable.html>

docs/docs/ban-char-field.md

@@ -0,0 +1,40 @@
+---
+id: ban-char-field
+title: ban-char-field
+---
+
+Using `character` is likely a mistake and should almost always be replaced by `text` or `varchar`.
+
+From the postgres docs:
+
+> There is no performance difference among these three types, apart from
+> increased storage space when using the blank-padded type, and a few extra CPU
+> cycles to check the length when storing into a length-constrained column.
+> While character(n) has performance advantages in some other database systems,
+> there is no such advantage in PostgreSQL; in fact character(n) is usually the
+> slowest of the three because of its additional storage costs. In most
+> situations text or character varying should be used instead.
+
+<https://www.postgresql.org/docs/10/datatype-character.html>
+
+See the [`prefer-text-field`](./prefer-text-field.md) rule for info on the advantages of `text` over `varchar`.
+
+Instead of:
+
+```sql
+CREATE TABLE "app_user" (
+    "id" serial NOT NULL PRIMARY KEY,
+    "name" char(100) NOT NULL,
+    "email" character NOT NULL,
+);
+```
+
+Use:
+
+```sql
+CREATE TABLE "app_user" (
+    "id" serial NOT NULL PRIMARY KEY,
+    "name" varchar(100) NOT NULL,
+    "email" TEXT NOT NULL,
+);
+```

docs/docs/ban-drop-database.md

@@ -0,0 +1,6 @@
+---
+id: ban-drop-database
+title: ban-drop-database
+---
+
+Dropping a database may break existing clients.

docs/docs/changing-column-type.md

@@ -0,0 +1,11 @@
+---
+id: changing-column-type
+title: changing-column-type
+---
+
+Changing a column type requires an `ACCESS EXCLUSIVE` lock on the table which blocks reads.
+
+Changing the type of the column may also break other clients reading from the
+table.
+
+<https://www.postgresql.org/docs/current/sql-altertable.html#SQL-ALTERTABLE-NOTES>

docs/docs/cli.md

@@ -0,0 +1,65 @@
+---
+id: cli
+title: CLI
+---
+
+## Usage
+
+```bash
+# lint a file or multiple
+squawk migration_001.sql migration_002.sql migration_003.sql
+
+# lint from standard in
+cat migration.sql | squawk
+```
+
+### `squawk --help`
+
+```
+squawk
+Find problems in your SQL
+
+USAGE:
+    squawk [FLAGS] [OPTIONS] [paths]... [SUBCOMMAND]
+
+FLAGS:
+    -h, --help
+            Prints help information
+
+        --list-rules
+            List all available rules
+
+    -V, --version
+            Prints version information
+
+        --verbose
+            Enable debug logging output
+
+
+OPTIONS:
+        --dump-ast <dump-ast>
+            Output AST in JSON [possible values: Raw, Parsed, Debug]
+
+    -e, --exclude <exclude>...
+            Exclude specific warnings
+
+            For example: --exclude=require-concurrent-index-creation,ban-drop-database
+        --explain <explain>
+            Provide documentation on the given rule
+
+        --reporter <reporter>
+            Style of error reporting [possible values: Tty, Gcc, Json]
+
+        --stdin-filepath <stdin-filepath>
+            Path to use in reporting for stdin
+
+
+ARGS:
+    <paths>...
+            Paths to search
+
+
+SUBCOMMANDS:
+    help                Prints this message or the help of the given subcommand(s)
+    upload-to-github    Comment on a PR with Squawk's results
+```