The onstat -g afr option prints allocated memory fragments for a specified session or shared-memory pool. Each session is allocated a pool of shared memory.
IBM Informix Dynamic Server Version 10.00.UC1 -- On-Line -- Up 18:47:42 -- 43008 Kbytes Allocations for pool name dfm_pool: addr size memid 10ac8c000 192 overhead 10ac8d000 24352 dfm