My book is complete, many thanks to Hugo, Tony, and many others!

Sankar,

The printed/kindle editions have two more chapters:

Ch. 09: Concurrent Queries and Transaction Isolation Levels

A query that works splendidly in isolation can often fail miserably when put to work in

a live OLTP system, with real life concurrency. To make a bad situation worse, in many

cases such errors are subtle and intermittent, and therefore very difficult to reproduce

and understand. This chapter considers the case of reporting queries running against

tables that are being simultaneously modified, demonstrates how inconsistent results

can be returned, assesses the impact of various isolation levels, and considers how best

the defensive programmer can defend data integrity, while minimizing deadlocks.

Ch. 10: Developing Modifications that Survive Concurrency

Just like queries, modifications that work perfectly well in the isolated world of the

test database, can suddenly start misbehaving intermittently when run in a production

environment under conditions of concurrent access. The chapter covers some of the

problems that might occur when "competing" connections try to simultaneously update

the same data, and how to avoid them:

• lost modifications, a.k.a. lost updates – such problems occur when modifications

performed by one connection are overwritten by another; they typically occur

silently, and no errors are raised.

• resource contention errors – such as deadlocks and lock timeouts

• primary key and unique constraint violations – such problems occur when

different modifications attempt to insert one and the same row.

Thanks, Sankar, Alejandro, James, Adam, and Aaron!

Thank you, Piotr!