add doc page for pg configs (#170)

* add doc page for pg configs

Author: ChuckHend

docs/configuration.md

@@ -0,0 +1,34 @@
+# Configuring pg_vectorize
+
+## Changing the database
+
+To change the database that pg_vectorize background worker is connected to, you can use the following SQL command:
+
+```sql
+ALTER SYSTEM SET vectorize.database_name TO 'my_new_db';
+```
+
+Then, restart Postgres.
+
+## Changing Embedding and LLM base URLs
+
+All Embedding model and LLM providers can have their base URLs changed.
+
+For example, if you have an OpenAI compliant embedding or LLM server (such as [vLLM](https://github.com/vllm-project/vllm)), running at `https://api.myserver.com/v1`, you can change the base URL with the following SQL command:
+
+```sql
+ALTER SYSTEM SET vectorize.openai_base_url TO 'https://api.myserver.com/v1';
+SELECT pg_reload_conf();
+```
+
+## Changing the batch job size
+
+Text data stored in Postgres is transformed into embeddings via HTTP requests made from the pg_vectorize background worker. Requests are made to the specified embedding service in batch (multiple inputs per request). The number of inputs per request is determined by the `vectorize.batch_size` GUC. This has no impact on transformations that occur during `vectorize.search()`, `vectorize.encode()` and `vectorize.rag()` which are always batch size 1 since those APIs accept only a single input (the raw text query).
+
+```sql
+ALTER SYSTEM SET vectorize.batch_size to 100;
+```
+
+## Available GUCs
+
+The complete list of GUCs available for pg_vectorize are defined in [extension/src/guc.rs](https://github.com/tembo-io/pg_vectorize/blob/638b12887f14d47de0793b16d535b226d8f371b9/extension/src/guc.rs#L33).

mkdocs.yml

@@ -25,6 +25,7 @@ nav:
       - 'examples/openai_embeddings.md'
       - 'examples/scheduling.md'
   - Model Providers: 'models/index.md'
+  - Extension Configuration: 'configuration.md'
 markdown_extensions:
 - toc:
     permalink: true