SAP Note 16063 - SAPDBA: index tablespace too small during reorg.

Symptom:

Reorganization of a table terminates with a message stating that the index tablespace is too small.

Cause and prerequisites

The index tablespace is too small. In this case, however, "too small" can also mean that the fragmentation of the available space is so great that the index/indices for reorganization (n extents -> 1 extent) no longer fit in the tablespace.

Solution
SAPDBA offers many different display options:
Free space analysis: Reorganization -> Check ->
Tablespace fragmentation (summary)
Detailed analysis: Reorganization -> Check -> Tablespace fragmentation (all extents)
When too little absolute free space is available, or the fragmentation of the available free space is too great, expand the index tablespace to enable the table reorganization to start. In the long term, you should also schedule a reorganization of the entire index tablespace.