To see a wonderful example of this, Figure 6-39 shows the inactive transactions flag change as a direct result of issuing a simple a select statement that touches block 1,78547.

Figure 6-39. Shown is a data block (1,75847) dumped immediately after a simple select statement touched the block. Notice the transaction flags have changed from a --U- to a C---, indicating a block cleanout has occurred.

Now I realize this is interesting and all that, but I also understand some readers may think this block dump and ITL stuff is not all that relevant. But I beg to differ. Not only have you gained a fuller understanding of the TX enqueue, but you have also clearly seen how Oracle implements its patented row-level locking scheme, In the next section, you will see how ITLs are involved with the "snapshot too old" error and with buffer cloning!