Bump default version; add upgrade script

[jasonmp85]

Adding a new UDF means adding an upgrade script to augment existing installations of pg_shard.

fixes #69

[coveralls]

Coverage remained the same at 93.2% when pulling 78ffe34 on feature-upgrade_script-#69 into 9838e1f on develop.

[sumedhpathak]

So how does this work? Will both files be executed on a CREATE EXTENSION command?

As I understand, and ALTER EXTENSION UPDATE on a 1.0 installation will add the new UDF.

Should we be moving the UDF to the 1.1 file, and keeping the above line as pg_shard--1.1.sql only? If I run a CREATE EXTENSION, shouldn't I expect the 1.1 file to include everything?
I'm not sure, so I'm just asking.

[jasonmp85]

So how does this work? Will both files be executed on a CREATE EXTENSION command?

No, the extension will come with exactly one version: 1.1. If you want 1.0 you'd download that version instead.

So for installing from scratch, the 1.1 script is used. For upgrading from 1.0, PostgreSQL will route a path from 1.0 to 1.1. Here it's trivial (a single file), so it'll execute that to perform the upgrade.

Should we be moving the UDF to the 1.1 file, and keeping the above line as pg_shard--1.1.sql only?

The UDF is already in the 1.1 file. We checked it into 1.0, but this Pull Request renames the file to 1.1. The 1.1 standalone file should include everything (double check for me).

If I run a CREATE EXTENSION, shouldn't I expect the 1.1 file to include everything?

It does. Don't think about the code in develop's history. Think about the history of releases. We released a 1.0 file in December. That's the only public install file so far. So for a 1.1 release we need two things:

• A 1.1 install file, to install 1.1 from scratch
• A 1.0-to-1.1 upgrade file, containing the delta between 1.0 and 1.1

This change renames the "main" install file to 1.1, satisfying the first requirement above and adds the upgrade script, satisfying the second.

[sumedhpathak]

The UDF is already in the 1.1 file. We checked it into 1.0, but this Pull Request renames the file to 1.1. The 1.1 standalone file should include everything (double check for me).

Ah, ok. That part I didn't realize. For some reason, I thought the UDF was only in the 1.0-1.1.sql file. The rest of it makes sense then. I checked, and the 1.1 sql file looks good.

[sumedhpathak]

One last question then. The create-extension command also supports a version. If I specify create-extension version 1.0, would that work? (And create 1.0 without the UDF?)

After checking on that, and assuming we've tested 1.0-1.1 upgrade and a 1.1 fresh install, you're good to

[jasonmp85]

The only way to install version 1.0 would be to download 1.0 and use that. The state of affairs for our extensions seems to be:

• The latest download contains a script to install that latest version
• It also contains upgrade scripts from earlier versions

[jasonmp85]

As a sanity check, I looked over at cstore, which looks exactly like pg_shard will after this Pull Request.

[jasonmp85]

Testing (not currently automated in any fashion):

• Checked out tag v1.0.2 and ran make uninstall; make install. This places the control and 1.0 SQL file in my PostgreSQL extension area
• Checked out this branch and ran make uninstall; make install. This replaces the control file with one defining 1.1 as the default version and adds the 1.1 upgrade (and install) script. This does not remove the 1.0 install script added by the first step
• Modified the init.sql in our tests to first install 1.0 and then upgrade to the latest known version
• Ran tests and verified they passed

Here is the SQL for the upgrade:

CREATE EXTENSION pg_shard VERSION '1.0';
ALTER EXTENSION pg_shard UPDATE;
# \dx
#                                List of installed extensions
#    Name   | Version |   Schema   |                       Description                       
# ----------+---------+------------+---------------------------------------------------------
#  pg_shard | 1.1     | public     | extension for sharding across remote PostgreSQL servers
#  plpgsql  | 1.0     | pg_catalog | PL/pgSQL procedural language
# (2 rows)

[jasonmp85]

So yeah, the two caveats are:

• Future versions don't remove the "main" install script from previous versions
• Our CI system (Travis) isn't currently testing upgrade paths (these could become numerous as time goes on anyhow, so we'll have to see how much support we need for previous versions before we go down the road of automating this).

But this patch works, works with an upgrade from 1.0, and matches what we're doing in cstore.