don't cache non-existant files

[russ]

susanne uploaded a new ntds index page, but neglected to upload one of the images.

 http://www.plosntds.org/images/home/article_v03_i02_junghanss.jpg gave a page not found error.

that error was cached in VirtualJournalMappingFilter?, with the key PLoSNTD-/images/home/article_v03_i02_junghanss.jpg

VJMF is an eternal cache. when the image was uploaded, it continued to return page not found for the image, until the cache key was forcibly removed.

VJMF should be smarter than this.

[russ]

pradeep suggests testing performance with and without VJM cache enabled - it's probably not providing any value, and could be scrapped as the easiest resolution to this issue.

[russ]

if VJMF doesn't provide a significant performance benefit, let's get rid of it.

to test, set maxelements to 0 and disable overflow to disk for VJMF, and run some performance tests (probably worth waiting for scott's perf test script to be complete so we can compare apples to apples)

since VJMF caches paths for asset URLs, any performance testing must download attached images, css, etc. when loading pages.

[wtoconnor]

(In [7610]) VJMF is an eternal cache. It will cache the error that results from trying to map things that do not exist. This will persist even when the thing is ingested and does exist. Addresses #1122

[wtoconnor]

VJMF has been removed.

[rcave]

Confirmed that Ambra is performing correctly in production with the VJMF disabled.