Google Cloud Storage provides strong data consistency: once a write completes, a read from anywhere in the world will get the most recent data.
However, if you enable caching (which by default is true for any publicly readable object), reads of that object can see a version of the object as old as the Cache-Control max-age specified on the object. If, for example, you uploaded the file like this:
gsutil cp -a public-read file gs://my_bucket/file
You can see that the max-age is 1 hour (3600 seconds):
gsutil ls -L gs://my_bucket/file
gs://my_bucket/file:
Creation time: Fri, 21 Dec 2012 19:59:57 GMT
Cache-Control: public, max-age=3600, no-transform
Content-Length: 1065
Content-Type: text/plain
ETag: eb3fb83beedf1efffe5b8e32e8d6a65a
...
If you want to prevent a publicly readable object from being cached you could do:
gsutil setmeta -h Cache-Control:no-cache gs://my_bucket/file
Alternatively, you could set a shorter max-age on the object:
gsutil setmeta -h 'Cache-Control:public, max-age=600, no-transform'
Mike Schwartz, Google Cloud Storage team