Re: Index split WAL reduction

Here's an updated patch that fixes a bug with full_page_writes, and an
alignment issue in replay code. Also added a new test case to
crashtest.sh that exercises the fixed bug.

Has anyone looked at this? I now consider it ready for committing, if
no-one sees a problem with it.

Here's the original description of the patch:

> Currently, an index split writes all the data on the split page to
> WAL. That's a lot of WAL traffic. The tuples that are copied to the
> right page need to be WAL logged, but the tuples that stay on the
> original page don't.
>
> Here's a patch to do that. It needs further testing, I have used the
> attached crude crashtest.sh to test the basics, but we need to test
> the more obscure cases like splitting non-leaf or root page.
>
> On a test case that inserts 10000 rows in increasing key order with a
> 100 characters wide text-field as key, the patch reduced the total
> generated WAL traffic from 45MB to 33MB, or ~ 25%. Your mileage may
> vary, depending on the tuple and key sizes, and the order of inserts.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com