Improve performance of loading ping body previews

Defer loading body_raw, instead load its first 150 bytes
as "body_raw_preview". This reduces both network I/O to database,
and disk I/O on the database host if the database contains large
request bodies.

cc: #1023

CHANGELOG.md

@@ -3,6 +3,9 @@ All notable changes to this project will be documented in this file.
 
 ## v3.5-dev - Unreleased
 
+### Improvements
+- Improve performance of loading ping body previews (#1023)
+
 ### Bug Fixes
 - Fix Check.ping() to lock the check before updating (#1023)
 

hc/front/templatetags/hc_extras.py

@@ -282,3 +282,8 @@ def fix_asterisks(s: str) -> str:
 @register.filter
 def pct(v: float) -> str:
     return str(int(v * 10000) / 100)
+
+
+@register.filter
+def decode(v: bytes) -> str:
+    return bytes(v).decode(errors="replace")

hc/front/views.py

@@ -26,6 +26,7 @@ from django.contrib.auth.models import User
 from django.core import signing
 from django.core.exceptions import PermissionDenied
 from django.db.models import Case, Count, F, Q, QuerySet, When
+from django.db.models.functions import Substr
 from django.http import (
     Http404,
     HttpRequest,
@@ -867,6 +868,11 @@ def _get_events(
             kinds_filter = kinds_filter | Q(kind__isnull=True) | Q(kind="")
         pq = pq.filter(kinds_filter)
 
+    # Optimization: defer loading body_raw, instead load its first 150 bytes
+    # as "body_raw_preview". This reduces both network I/O to database, and disk I/O
+    # on the database host if the database contains large request bodies.
+    pq = pq.defer("body_raw")
+    pq = pq.annotate(body_raw_preview=Substr("body_raw", 1, 151))
     pings = list(pq[:page_limit])
 
     # Optimization: the template will access Ping.duration, which would generate a

templates/front/log_row.html

@@ -17,7 +17,7 @@
 {% if event.rid %}<span class="label rid">{{ event.rid|first5 }}</span> {% endif %}
 {% if event.scheme == "email" %}{{ event.ua }}{% else %}
 {{ event.scheme|upper }} {{ event.method }}{% if event.remote_addr %} from {{ event.remote_addr }}{% endif %}
-<code>{% if event.body_raw %}- {{ event.get_body|truncatechars:150 }}{% elif event.object_size %}- {{ event.object_size }} byte body{% endif %}{% if event.ua %} - {{ event.ua|truncatechars:80 }}{% endif %}</code>
+<code>{% if event.body_raw_preview %}- {{ event.body_raw_preview|decode }}{% elif event.object_size %}- {{ event.object_size }} byte body{% endif %}{% if event.ua %} - {{ event.ua|truncatechars:80 }}{% endif %}</code>
 {% endif %}
 </td>
 </tr>