Not Updating Customized Table when System having Performance Issue

Dear Gurus,

I've built an user exit in MM using EXIT_SAPLMBMB_001

. This userexit is triggered whenever a material document is created. This userexit in turns call a function module that write information to a customized table ZMCHA.

During normal operations, this function has been working fine. Both MCHA and ZMCHB is updated. However during performance issue times, only MCHA table is updated and not ZMCHB.

I've tried a commit statement inside the function module but i've got an abap dump. Function Module used for Commit is DB_COMMIT.

Please let me know if anybody has encounter such issues. Thanks in advance

Regards

Leonard