create_database checks existence twice (3 RTTs)

[ricellis]

I was doing some testing and noticed that the create_database call makes two GET requests before the PUT to create a remote database. This is what happens:

1. client.create_database() calls database.exists() which does a GET
2. If it didn't exist client.create_database() calls database.create()
3. database.create() calls exists() which does another GET
4. If the database does not exist then database.create() finally does the PUT.

I think it could be beneficial to replace these three round trips with a single request to PUT given that if the database already exists a 412 is returned. There is some complication in that currently database.create() would not throw for the 412 response case, but client.create_database optionally needs to throw.

• Cloudant (python-cloudant) version(s) that are affected by this issue.
  • 2.0.0b2 (probably others too)
• Python version
  • any (tested on 2.7)
• A small code sample that demonstrates the issue.

client.create_database('abc')

[alfinkel]

These are now HEAD calls rather than GET fwiw but imo at least one of the HEAD calls should be removed. See my comments on #279.