From 689cf9c139f57d6a3fd61e0c62fe66c793f234ae Mon Sep 17 00:00:00 2001
From: Simon Willison <swillison@gmail.com>
Date: Wed, 15 May 2019 20:02:33 -0700
Subject: [PATCH] Index page only shows row counts for smaller databases

The index page now only shows row counts for immutable databases OR for
databases with less than 30 tables provided it could get a count for
each of those tables in less than 10ms.

Closes #467, Refs #460
---
 datasette/templates/index.html |  4 ++--
 datasette/views/index.py       | 22 +++++++++++++++++-----
 tests/test_api.py              |  1 +
 3 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/datasette/templates/index.html b/datasette/templates/index.html
index 58956582..c8ad4148 100644
--- a/datasette/templates/index.html
+++ b/datasette/templates/index.html
@@ -12,9 +12,9 @@
 {% for database in databases %}
     <h2 style="padding-left: 10px; border-left: 10px solid #{{ database.color }}"><a href="{{ database.path }}">{{ database.name }}</a></h2>
     <p>
-        {{ "{:,}".format(database.table_rows_sum) }} rows in {{ database.tables_count }} table{% if database.tables_count != 1 %}s{% endif %}{% if database.tables_count and database.hidden_tables_count %}, {% endif -%}
+        {% if database.show_table_row_counts %}{{ "{:,}".format(database.table_rows_sum) }} rows in {% endif %}{{ database.tables_count }} table{% if database.tables_count != 1 %}s{% endif %}{% if database.tables_count and database.hidden_tables_count %}, {% endif -%}
         {% if database.hidden_tables_count -%}
-            {{ "{:,}".format(database.hidden_table_rows_sum) }} rows in {{ database.hidden_tables_count }} hidden table{% if database.hidden_tables_count != 1 %}s{% endif -%}
+            {% if database.show_table_row_counts %}{{ "{:,}".format(database.hidden_table_rows_sum) }} rows in {% endif %}{{ database.hidden_tables_count }} hidden table{% if database.hidden_tables_count != 1 %}s{% endif -%}
         {% endif -%}
         {% if database.views_count -%}
             {% if database.tables_count or database.hidden_tables_count %}, {% endif -%}
diff --git a/datasette/views/index.py b/datasette/views/index.py
index d383b730..bca901f5 100644
--- a/datasette/views/index.py
+++ b/datasette/views/index.py
@@ -14,8 +14,12 @@ from datasette.version import __version__
 from .base import HASH_LENGTH, RenderMixin
 
 
+# Truncate table list on homepage at:
 TRUNCATE_AT = 5
 
+# Only attempt counts if less than this many tables:
+COUNT_TABLE_LIMIT = 30
+
 
 class IndexView(RenderMixin):
     name = "index"
@@ -26,11 +30,18 @@ class IndexView(RenderMixin):
     async def get(self, request, as_format):
         databases = []
         for name, db in self.ds.databases.items():
-            table_counts = await db.table_counts(5)
-            views = await db.view_names()
-            tables = {}
+            table_names = await db.table_names()
             hidden_table_names = set(await db.hidden_table_names())
-            for table in table_counts:
+            views = await db.view_names()
+            # Perform counts only for immutable or DBS with <= COUNT_TABLE_LIMIT tables
+            table_counts = {}
+            if not db.is_mutable or len(table_names) <= COUNT_TABLE_LIMIT:
+                table_counts = await db.table_counts(10)
+                # If any of these are None it means at least one timed out - ignore them all
+                if any(v is None for v in table_counts.values()):
+                    table_counts = {}
+            tables = {}
+            for table in table_names:
                 table_columns = await self.ds.table_columns(name, table)
                 tables[table] = {
                     "name": table,
@@ -38,7 +49,7 @@ class IndexView(RenderMixin):
                     "primary_keys": await self.ds.execute_against_connection_in_thread(
                         name, lambda conn: detect_primary_keys(conn, table)
                     ),
-                    "count": table_counts[table],
+                    "count": table_counts.get(table),
                     "hidden": table in hidden_table_names,
                     "fts_table": await self.ds.execute_against_connection_in_thread(
                         name, lambda conn: detect_fts(conn, table)
@@ -74,6 +85,7 @@ class IndexView(RenderMixin):
                     > TRUNCATE_AT,
                     "tables_count": len(visible_tables),
                     "table_rows_sum": sum((t["count"] or 0) for t in visible_tables),
+                    "show_table_row_counts": bool(table_counts),
                     "hidden_table_rows_sum": sum(
                         t["count"] for t in hidden_tables if t["count"] is not None
                     ),
diff --git a/tests/test_api.py b/tests/test_api.py
index 00c884a7..ea5d2a2d 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -445,6 +445,7 @@ def test_no_files_uses_memory_database(app_client_no_files):
             "hidden_table_rows_sum": 0,
             "hidden_tables_count": 0,
             "name": ":memory:",
+            "show_table_row_counts": False,
             "path": "/:memory:",
             "table_rows_sum": 0,
             "tables_count": 0,