feat: allow Python and Typescript users to create Sessions (#2530)

## Summary
- Exposes `Session` in Python and Typescript so users can set the
`index_cache_size_bytes` and `metadata_cache_size_bytes`
* The `Session` is attached to the `Connection`, and thus shared across
all tables in that connection.
- Adds deprecation warnings for table-level cache configuration


🤖 Generated with [Claude Code](https://claude.ai/code)

---------

Co-authored-by: Claude <noreply@anthropic.com>

docs/src/js/classes/Session.md

@@ -0,0 +1,84 @@
+[**@lancedb/lancedb**](../README.md) • **Docs**
+
+***
+
+[@lancedb/lancedb](../globals.md) / Session
+
+# Class: Session
+
+A session for managing caches and object stores across LanceDB operations.
+
+Sessions allow you to configure cache sizes for index and metadata caches,
+which can significantly impact performance for large datasets.
+
+## Constructors
+
+### new Session()
+
+```ts
+new Session(indexCacheSizeBytes?, metadataCacheSizeBytes?): Session
+```
+
+Create a new session with custom cache sizes.
+
+# Parameters
+
+- `index_cache_size_bytes`: The size of the index cache in bytes.
+  Defaults to 6GB if not specified.
+- `metadata_cache_size_bytes`: The size of the metadata cache in bytes.
+  Defaults to 1GB if not specified.
+
+#### Parameters
+
+* **indexCacheSizeBytes?**: `null` \| `bigint`
+
+* **metadataCacheSizeBytes?**: `null` \| `bigint`
+
+#### Returns
+
+[`Session`](Session.md)
+
+## Methods
+
+### approxNumItems()
+
+```ts
+approxNumItems(): number
+```
+
+Get the approximate number of items cached in the session.
+
+#### Returns
+
+`number`
+
+***
+
+### sizeBytes()
+
+```ts
+sizeBytes(): bigint
+```
+
+Get the current size of the session caches in bytes.
+
+#### Returns
+
+`bigint`
+
+***
+
+### default()
+
+```ts
+static default(): Session
+```
+
+Create a session with default cache sizes.
+
+This is equivalent to creating a session with 6GB index cache
+and 1GB metadata cache.
+
+#### Returns
+
+[`Session`](Session.md)

docs/src/js/functions/connect.md

@@ -6,10 +6,13 @@
 
 # Function: connect()
 
-## connect(uri, options)
+## connect(uri, options, session)
 
 ```ts
-function connect(uri, options?): Promise<Connection>
+function connect(
+   uri,
+   options?,
+   session?): Promise<Connection>
 ```
 
 Connect to a LanceDB instance at the given URI.
@@ -29,6 +32,8 @@ Accepted formats:
 * **options?**: `Partial`&lt;[`ConnectionOptions`](../interfaces/ConnectionOptions.md)&gt;
     The options to use when connecting to the database
 
+* **session?**: [`Session`](../classes/Session.md)
+
 ### Returns
 
 `Promise`&lt;[`Connection`](../classes/Connection.md)&gt;
@@ -77,7 +82,7 @@ Accepted formats:
 
 [ConnectionOptions](../interfaces/ConnectionOptions.md) for more details on the URI format.
 
-### Example
+### Examples
 
 ```ts
 const conn = await connect({
@@ -85,3 +90,11 @@ const conn = await connect({
   storageOptions: {timeout: "60s"}
 });
 ```
+
+```ts
+const session = Session.default();
+const conn = await connect({
+  uri: "/path/to/database",
+  session: session
+});
+```

docs/src/js/globals.md

@@ -29,6 +29,7 @@
 - [Query](classes/Query.md)
 - [QueryBase](classes/QueryBase.md)
 - [RecordBatchIterator](classes/RecordBatchIterator.md)
+- [Session](classes/Session.md)
 - [Table](classes/Table.md)
 - [TagContents](classes/TagContents.md)
 - [Tags](classes/Tags.md)

docs/src/js/interfaces/ConnectionOptions.md

@@ -70,6 +70,17 @@ Defaults to 'us-east-1'.
 
 ***
 
+### session?
+
+```ts
+optional session: Session;
+```
+
+(For LanceDB OSS only): the session to use for this connection. Holds
+shared caches and other session-specific state.
+
+***
+
 ### storageOptions?
 
 ```ts

docs/src/js/interfaces/OpenTableOptions.md

@@ -8,7 +8,7 @@
 
 ## Properties
 
-### indexCacheSize?
+### ~~indexCacheSize?~~
 
 ```ts
 optional indexCacheSize: number;
@@ -16,6 +16,11 @@ optional indexCacheSize: number;
 
 Set the size of the index cache, specified as a number of entries
 
+#### Deprecated
+
+Use session-level cache configuration instead.
+Create a Session with custom cache sizes and pass it to the connect() function.
+
 The exact meaning of an "entry" will depend on the type of index:
 - IVF: there is one entry for each IVF partition
 - BTREE: there is one entry for the entire index