change to partial index

Author: nikolayk812

README.md

@@ -39,7 +39,7 @@ CREATE TABLE IF NOT EXISTS outbox_messages
     published_at TIMESTAMP
 );
 
-CREATE INDEX idx_outbox_messages_published_at ON outbox_messages (published_at);
+CREATE INDEX IF NOT EXISTS idx_outbox_messages_published_at_null ON outbox_messages (published_at) WHERE published_at IS NULL;
 ```
 
 The outbox table name can be customized, but the table structure should remain exactly the same.
@@ -128,4 +128,10 @@ Source code and instructions for the example are located in the [examples/01_sns
 
 ## Stargazers over time
 
-[![Stargazers over time](https://starchart.cc/nikolayk812/pgx-outbox.svg?variant=adaptive)](https://starchart.cc/nikolayk812/pgx-outbox)
+[![Stargazers over time](https://starchart.cc/nikolayk812/pgx-outbox.svg?variant=adaptive)](https://starchart.cc/nikolayk812/pgx-outbox)
+
+## Alternatives
+
+- [Trendyol/go-pq-cdc](https://github.com/Trendyol/go-pq-cdc) - Change Data Capture (CDC) library for PostgreSQL
+- [watermill-sql](https://github.com/ThreeDotsLabs/watermill-sql) - PostgreSQL Pub/Sub for Watermill
+- [dataddo/pgq](https://github.com/dataddo/pgq) - Go queue implementation using PostgreSQL

internal/sql/01_outbox_messages.down.sql

@@ -1,2 +1,2 @@
-DROP INDEX IF EXISTS idx_outbox_messages_published_at;
+DROP INDEX IF EXISTS idx_outbox_messages_published_at_null;
 DROP TABLE IF EXISTS outbox_messages;

internal/sql/01_outbox_messages.up.sql

@@ -11,4 +11,5 @@ CREATE TABLE IF NOT EXISTS outbox_messages
     published_at TIMESTAMP
 );
 
-CREATE INDEX IF NOT EXISTS idx_outbox_messages_published_at ON outbox_messages (published_at);
+-- https://www.postgresql.org/docs/current/indexes-partial.html
+CREATE INDEX IF NOT EXISTS idx_outbox_messages_published_at_null ON outbox_messages (published_at) WHERE published_at IS NULL;