If Console is streaming log messages, typing a URL in Safari's location field will often lag before showing results. This is due to the UnifiedFieldCompletionListGenerator class sending thousands of logging messages via os_log_info().

To fix this, create a plist with the following content:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>URLAutocomplete</key>
    <dict>
        <key>Level</key>
        <dict>
            <key>Enable</key>
            <string>Off</string>
            <key>Persist</key>
            <string>Off</string>
        </dict>
    </dict>
</dict>
</plist>

Then copy it to /Library/Preferences/Logging/Subsystems/com.apple.Safari.plist:

sudo mkdir -p /Library/Preferences/Logging/Subsystems
sudo cp TheExamplePlist.plist /Library/Preferences/Logging/Subsystems/com.apple.Safari.plist