From 7944a8b0de9f892713da9d31ef0085cd9bcc5ff3 Mon Sep 17 00:00:00 2001
From: Simon Willison <swillison@gmail.com>
Date: Sat, 26 May 2018 17:43:22 -0700
Subject: [PATCH] Added num_sql_threads config option, closes #285

---
 datasette/app.py  | 9 ++++++---
 docs/config.rst   | 9 +++++++++
 tests/test_api.py | 1 +
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/datasette/app.py b/datasette/app.py
index b048c67e..b512fdb5 100644
--- a/datasette/app.py
+++ b/datasette/app.py
@@ -59,6 +59,9 @@ CONFIG_OPTIONS = (
     ConfigOption("max_returned_rows", 1000, """
         Maximum rows that can be returned from a table or custom query
     """.strip()),
+    ConfigOption("num_sql_threads", 3, """
+        Number of threads in the thread pool for executing SQLite queries
+    """.strip()),
     ConfigOption("sql_time_limit_ms", 1000, """
         Time limit for a SQL query in milliseconds
     """.strip()),
@@ -124,7 +127,6 @@ class Datasette:
     def __init__(
         self,
         files,
-        num_threads=3,
         cache_headers=True,
         cors=False,
         inspect_data=None,
@@ -136,8 +138,6 @@ class Datasette:
         config=None,
     ):
         self.files = files
-        self.num_threads = num_threads
-        self.executor = futures.ThreadPoolExecutor(max_workers=num_threads)
         self.cache_headers = cache_headers
         self.cors = cors
         self._inspect = inspect_data
@@ -148,6 +148,9 @@ class Datasette:
         self.plugins_dir = plugins_dir
         self.static_mounts = static_mounts or []
         self.config = dict(DEFAULT_CONFIG, **(config or {}))
+        self.executor = futures.ThreadPoolExecutor(
+            max_workers=self.config["num_sql_threads"]
+        )
         self.max_returned_rows = self.config["max_returned_rows"]
         self.sql_time_limit_ms = self.config["sql_time_limit_ms"]
         self.page_size = self.config["default_page_size"]
diff --git a/docs/config.rst b/docs/config.rst
index a8b466a5..25bfd3d5 100644
--- a/docs/config.rst
+++ b/docs/config.rst
@@ -38,6 +38,15 @@ You can increase or decrease this limit like so::
 
     datasette mydatabase.db --config max_returned_rows:2000
 
+num_sql_threads
+---------------
+
+Maximum number of threads in the thread pool Datasette uses to execute SQLite queries. Defaults to 3.
+
+::
+
+    datasette mydatabase.db --config num_sql_threads:10
+
 allow_facet
 -----------
 
diff --git a/tests/test_api.py b/tests/test_api.py
index 1ec50b09..455ff864 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -940,6 +940,7 @@ def test_config_json(app_client):
         "suggest_facets": True,
         "allow_sql": True,
         "default_cache_ttl": 365 * 24 * 60 * 60,
+        "num_sql_threads": 3,
     } == response.json