add postgres kvstoreimpl (#374)

* add postgres kvstoreimpl

* make table name configurable

* add validator for table name

* linter fix

---------

Co-authored-by: Dinesh Yeduguru <dineshyv@fb.com>

llama_stack/providers/utils/kvstore/postgres/postgres.py

@@ -0,0 +1,103 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+from datetime import datetime
+from typing import List, Optional
+
+import psycopg2
+from psycopg2.extras import DictCursor
+
+from ..api import KVStore
+from ..config import PostgresKVStoreConfig
+
+
+class PostgresKVStoreImpl(KVStore):
+    def __init__(self, config: PostgresKVStoreConfig):
+        self.config = config
+        self.conn = None
+        self.cursor = None
+
+    async def initialize(self) -> None:
+        try:
+            self.conn = psycopg2.connect(
+                host=self.config.host,
+                port=self.config.port,
+                database=self.config.db,
+                user=self.config.user,
+                password=self.config.password,
+            )
+            self.conn.autocommit = True
+            self.cursor = self.conn.cursor(cursor_factory=DictCursor)
+
+            # Create table if it doesn't exist
+            self.cursor.execute(
+                f"""
+                CREATE TABLE IF NOT EXISTS {self.config.table_name} (
+                    key TEXT PRIMARY KEY,
+                    value TEXT,
+                    expiration TIMESTAMP
+                )
+                """
+            )
+        except Exception as e:
+            import traceback
+
+            traceback.print_exc()
+            raise RuntimeError("Could not connect to PostgreSQL database server") from e
+
+    def _namespaced_key(self, key: str) -> str:
+        if not self.config.namespace:
+            return key
+        return f"{self.config.namespace}:{key}"
+
+    async def set(
+        self, key: str, value: str, expiration: Optional[datetime] = None
+    ) -> None:
+        key = self._namespaced_key(key)
+        self.cursor.execute(
+            f"""
+            INSERT INTO {self.config.table_name} (key, value, expiration)
+            VALUES (%s, %s, %s)
+            ON CONFLICT (key) DO UPDATE
+            SET value = EXCLUDED.value, expiration = EXCLUDED.expiration
+            """,
+            (key, value, expiration),
+        )
+
+    async def get(self, key: str) -> Optional[str]:
+        key = self._namespaced_key(key)
+        self.cursor.execute(
+            f"""
+            SELECT value FROM {self.config.table_name}
+            WHERE key = %s
+            AND (expiration IS NULL OR expiration > NOW())
+            """,
+            (key,),
+        )
+        result = self.cursor.fetchone()
+        return result[0] if result else None
+
+    async def delete(self, key: str) -> None:
+        key = self._namespaced_key(key)
+        self.cursor.execute(
+            f"DELETE FROM {self.config.table_name} WHERE key = %s",
+            (key,),
+        )
+
+    async def range(self, start_key: str, end_key: str) -> List[str]:
+        start_key = self._namespaced_key(start_key)
+        end_key = self._namespaced_key(end_key)
+
+        self.cursor.execute(
+            f"""
+            SELECT value FROM {self.config.table_name}
+            WHERE key >= %s AND key < %s
+            AND (expiration IS NULL OR expiration > NOW())
+            ORDER BY key
+            """,
+            (start_key, end_key),
+        )
+        return [row[0] for row in self.cursor.fetchall()]