Auto merge of #2144 - jtgeibel:prod/fix-db-dump-fallback, r=smarnach

Allow database dumps to be run against the read-only replica

Edit: The description has been updated, with the original message included below.

This PR updates the database dump script so that it can be run against the read-only replica database.

I've tested locally, but we can manually schedule a database dump against the read-only replica and then update the existing daily scheduled task.

## Original PR Description

In production, the scheduler was configured to run:

```
./target/release/enqueue-job dump_db $READ_ONLY_REPLICA
```

instead of:

```
./target/release/enqueue-job dump_db $READ_ONLY_REPLICA_URL
```

Because of the typo in the variable name, the dump_db job has been
running against the primary database.  This patch modifies the fallback
to ensure the primary database is only used if explicitly provided.

Author: bors

src/bin/enqueue-job.rs

@@ -13,7 +13,7 @@ fn main() -> Result<(), Error> {
     match &*job {
         "update_downloads" => Ok(tasks::update_downloads().enqueue(&conn)?),
         "dump_db" => {
-            let database_url = args.next().unwrap_or_else(|| env("DATABASE_URL"));
+            let database_url = args.next().unwrap_or_else(|| env("READ_ONLY_REPLICA_URL"));
             let target_name = args
                 .next()
                 .unwrap_or_else(|| String::from("db-dump.tar.gz"));

src/tasks/dump_db/dump-export.sql.hbs

@@ -1,19 +1,7 @@
-BEGIN;
+BEGIN ISOLATION LEVEL REPEATABLE READ, READ ONLY;
 {{~#each tables}}
 {{~#if this.filter}}
-    CREATE TEMPORARY VIEW "dump_db_{{this.name}}" AS (
-        SELECT {{this.columns}}
-        FROM "{{this.name}}"
-        WHERE {{this.filter}}
-    );
-{{~/if}}
-{{~/each}}
-COMMIT;
-
-BEGIN ISOLATION LEVEL SERIALIZABLE READ ONLY DEFERRABLE;
-{{~#each tables}}
-{{~#if this.filter}}
-    \copy (SELECT * FROM "dump_db_{{this.name}}") TO 'data/{{this.name}}.csv' WITH CSV HEADER
+    \copy (SELECT {{this.columns}} FROM "{{this.name}}" WHERE {{this.filter}}) TO 'data/{{this.name}}.csv' WITH CSV HEADER
 {{~else}}
     \copy "{{this.name}}" ({{this.columns}}) TO 'data/{{this.name}}.csv' WITH CSV HEADER
 {{~/if}}

src/tasks/dump_db/gen_scripts.rs

@@ -42,7 +42,7 @@ struct TableConfig {
 #[derive(Debug, Serialize)]
 struct HandlebarsTableContext<'a> {
     name: &'a str,
-    filter: Option<&'a str>,
+    filter: Option<String>,
     columns: String,
     column_defaults: BTreeMap<&'a str, &'a str>,
 }
@@ -59,7 +59,7 @@ impl TableConfig {
         if columns.is_empty() {
             None
         } else {
-            let filter = self.filter.as_ref().map(String::as_str);
+            let filter = self.filter.as_ref().map(|s| s.replace('\n', " "));
             let column_defaults = self
                 .column_defaults
                 .iter()