Does “WHERE 1=1” usually have an impact on query performance

It will take marginally longer to generate the plan when there are more indexes to consider, but I doubt the difference would be measurably significant. The reasons for dropping an index does not list query performance. On the other hand, in general you shouldn't create indexes unless you know they will be used to make a query more efficient.

From the Oracle Concepts Guide, here are the criteria for creating an index.

In general, consider creating an index on a column in any of the following situations:

• The indexed columns are queried frequently and return a small percentage of the total number of rows in the table.

• A referential integrity constraint exists on the indexed column or columns. The index is a means to avoid a full table lock that would otherwise be required if you update the parent table primary key, merge into the parent table, or delete from the parent table.

• A unique key constraint will be placed on the table and you want to manually specify the index and all index options.

All indexes will be considered in the sense that all indexes on the tables in the query are examined to determine whether they could be used. Those that could be are further examined to determine usefulness.

Jonathan Kehayias did a good blog post on NUMA at SQLSkills.com.

I believe server wise most of the vendors out there note if they are NUMA capable servers or not. From reading Jonathan's post it seems the focus is on the motherboard and processor capabilities. Then I would imagine how they interconnect would be an important thing to note as well, since that would be the bottleneck in most cases.

I have not really seen anyone write up on when NUMA becomes beneficial. I think it would just be a analysis on what your system is going to need. If one server maxed out to the nines is not going to cut it for the workload, then look at the alternatives.