pIndex file generated on disk are close to 10x size of the bucket size in memory

```
➜ data du -sch webnutshell_21809c13557138e3_* | grep total
592M total
➜ data /opt/couchbase/bin/cbstats 0:11210 -b webnutshell all | grep -w
mem_used
mem_used: 66951456
```

3 types of documents in this bucket(webnutshell), redacted some confidential customer info:

cluster_blob: https://gist.github.com/abhi-bit/6bbbcac3ff75d20b0e00
node_blob: https://gist.github.com/abhi-bit/a8892159fd684c510fb6
customer_blob: https://gist.github.com/abhi-bit/62882eae79602bcda77c

Also, I've noticed the ratio of cbft index files vs bucket mem_used to grow as bucket dataset size grows. From an earlier deployment experience, I've seen a bucket using ~1G in memory created indexes of size 190GB on disk - I've kick started indexing against that bucket couple of days back, will share numbers once the indexing is complete there.