I was curious to see where Server-Timing was implemented on the web, so I started searching the HTTP Archive for sites using it. Interestingly enough, there were no sites in the HTTP Archive that had Server-Timing response headers before 3/1/2017. Since then it’s usage has been gradually increasing each month. As of July 2017, there are 72 sites and 352 HTTP responses containing Server-Timing headers.
Here’s a query that I wrote to find a list of sites with Server-Timing headers. You can run it on BigQuery here :
SELECT p.url, p.rank, count(*) as freq
FROM
( SELECT pageid, url, rank
FROM [httparchive:runs.latest_pages]
) p
JOIN
( SELECT pageid,url,respOtherHeaders
FROM [httparchive:runs.latest_requests]
WHERE LOWER(respOtherHeaders) CONTAINS "server-timing"
) r
ON p.pageid = r.pageid
GROUP BY p.url, p.rank
ORDER BY freq DESC
Next I was curious to see the actual Server-Timing headers to understand how they are being used. I wrote this query to strip out the server-timing headers from the respOtherHeaders column. The query has a lot of string manipulations to extract the text. I’ve added some comments to the query to help make it easier to follow -
SELECT HOST(url), status, mimeType,
IF (
-- In respOtherHeaders, remove everything to the left of the server-timing header. Is there a ; in the remaining string?
RIGHT(respOtherHeaders,LENGTH(respOtherHeaders)-INSTR(LOWER(respOtherHeaders),"server-timing")+1) CONTAINS ";",
-- Then strip out everything to the left of the server-timing header and everything to the right of the ";" character.
LEFT(
RIGHT(respOtherHeaders,
LENGTH(respOtherHeaders)-INSTR(LOWER(respOtherHeaders),"server-timing")+1),
INSTR(
RIGHT(respOtherHeaders,
LENGTH(respOtherHeaders)-INSTR(LOWER(respOtherHeaders),
"server-timing")+1),
";")
),
-- If there are no ; chars, then the respOtherHeaders column ends with server-timing. Remove everything to the left of server-timing
RIGHT(respOtherHeaders,
LENGTH(respOtherHeaders)-INSTR(LOWER(respOtherHeaders),
"server-timing")+1)
) as ServerTimingHeader
FROM [httparchive:runs.latest_requests]
WHERE LOWER(respOtherHeaders) CONTAINS "server-timing"
You can see it on BigQuery here
Looking at the Server-Timing headers, I can see 3 different types of data being sent in these headers:
Timing Metrics - such as application time, gateway time, image resize time, etc
Server-Timing = app=133.99219512939;
Server-Timing = gateway-time=25;
Server-Timing = resizer=0.015;
server-timing = view=2.188, db=0.000, total=61.743, x-runtime = 0.069661, x-ua-compatible = ie=edge,chrome=1, x-frame-options = SAMEORIGIN
Server-Timing = app=53.393840789795;
Caching Information
server-timing = hit, cf-cache-status = HIT
server-timing = cold, cf-cache-status = MISS
server-timing = hit, cf-cache-status = HIT
server-timing = cold, cf-cache-status = MISS
Informational
server-timing = ibs_5318e9209631=1
server-timing = ibs_1964fd84c9cea3=1
server-timing = ibs_1880bf4b0f6311=1
Looking at all of the data in the 7/1/2017 tables, I can see that the current examples in the wild are split between these 3 types of data, although the caching ones are mostly on images, the informational ones are set on JS and responses w/ no content (ie, 204s -likely beacon responses), and the actual timing metrics are spread across a wide range of content.
It’ll be interesting to see how this evolves as Server-Timing adoption increases over time.
… on the bright side, there’s probably a common fix for all of them.