Performance issues with SRS requests when instance ID is not found

Overview:
Requests to /source-storage/records/{instanceId}/formatted?idType=INSTANCE perform intermittently poorly if the instance ID is not found.
Steps to Reproduce:
Run a series of requests to /source-storage/records/{instanceId}/formatted?idType=INSTANCE using a list of instance IDs, some of which can be found in SRS, some of which are not there (e.g. use a randomly generated UUID).

Expected Results:
All requests should perform about the same (return results or 404 in < 500ms)

Actual Results:
Intermittently, "not found" responses have a very high latency (50 seconds or more). It seems that this can also affect subsequent responses that are successful ("found").

A typical run of 100 requests with known UUIDs (all in SRS) gives this kind of result:

Getting 100 instances (offset 5556568).............
Made 100 lookup(s)
100 found
Min found resp time: 0.238017082214355
Avg found resp time: 0.284714541435242
Mean found time: 0.283137556338381
Max found resp time: 0.367691993713379
0 slow 'found' response(s)
0 not found
0 error(s)

A typical run of 100 requests with ~25% random UUIDs gives this result:

Getting 100 instances (offset 2510159).............
Made 100 lookup(s)
73 found
Min found resp time: 0.237093925476074
Avg found resp time: 1.76643755337963
Mean found time: 0.338731567634563
Max found resp time: 53.5151879787445
4 slow 'found' response(s)
27 not found
Min not found time: 0.228291988372803
Avg not found time: 4.32197585812321
Mean not found time: 0.368457941181954
Max not found time: 55.4095659255981
2 slow 'not found' response(s)
0 error(s)

Additional Information:
Tested against 2 Goldenrod installations and bugfest-honeysuckle.

Sample test script attached.

Interested parties:
jeffrey.fleming@duke.edu karen.newbery