Impact of bidding script size

[fabricegaignier]

We do observe that around 30% of the KV server calls are not followed by an execution of our bidding script (generateBid). The execution of generateBid, at its very beginning registers forDebuggingOnly.reportAdAuctionLoss so that we are sure to receive a notification server side if generateBid is triggered.

We investigated the impact of the size of the bidding script on that phenomenon.
For that we conducted two tests:

The first test is to increase the size of the production bidding script.

For that we add a dummy payload to the script. This payload can be of an arbitrary size.
We consider the size as seen server side before any compression mechanism.
The production bidding script if around 100KB

We use the no-cache response header, indicating that the script can be stored in caches, but the response must be validated with the origin server before each reuse.

We tested adding 100KB, 200KB, 400KB and 800KB

The second test is to reduce the size of the bidding script. For that we build a minimal bidding script where we remove all logic in generateBid. It only registers a call to forDebuggingOnly.reportAdAuctionLoss and returns a constant bid (-1). reportWin does nothing.

This minimal script is of size 1KB. We still have the capacity to add a dummy payload to it.
We tested with script sizes 1KB (the minimal script) and 25KB (the minimal script plus a dummy payload of 24KB)

The test ensures we have the same number of calls to the bidding script endpoint in the reference population and in the test population.

We measure the relative increase in participation as : (number of reports received in TEST - number of reports received in REF)/(number of reports received in REF)

The results show a clear relationship between the size of the bidding script and the number of generateBid executions :

size (KB)	relative increase in participation
1	+11.5%
25	+7.6%
100 (current size = reference)	0
200	-24%
300	-26%
500	-37%
900	-46%

This causes several issues

1. We are limited in improving our bidding logic and added value for our customers.
2. We suffer from a loss of opportunity while still fully supporting the infra-cost for these missed opportunities. The KV server is called while the bidding script is loading.

Are there any mitigation proposal to minimize this effect?
And more generally what would be the possible reporting solutions to measure why we lose opportunities (the size of the bidding script being one of them)?