Probably the only valid reason for using
set enable_seqscan=false
is when you're writing queries and want to quickly see what the query plan would actually be were there large amounts of data in the table(s).
The order the container uses in building the chain of filters to be applied for a particular request URI is as follows:
First, the <url-pattern> matching filter mappings in the same order that these elements appear in the deployment descriptor.
Next, the <servlet-name> matching filter mappings in the same order that these elements appear in the deployment descriptor.