process hunging

We have a batch process, most time it runs ok, sometime it hung forever. We use IDS 7.23uc3 on SUn solaris 2.5.1. What possible cause a process to hung in Informix? Help please. Thanks Jean Wang When the process hung, following was the status: INFORMIX-OnLine Version 7.22.UC1 -- On-Line -- Up 3 days 13:26:26 -- 1533368 K bytes session #RSAM total used id user tty pid hostname threads memory memory 1494 dwdev - 28302 icarus 6 237568 220672 tid name rstcb flags curstk status 243905 sqlexec 1e5d4e58 Y--P--- 1808 1e5d4e58 cond wait(sm_read) 243906 scan_1.0 1e5e6f58 Y------ 1312 1e5e6f58 cond wait(await_MC1) 243907 hjoin_2. 1e5d7498 Y------ 1312 1e5d7498 cond wait(await_MC2) 243908 join_3.0 1e5d56d8 Y------ 1312 1e5d56d8 cond wait(await_MC3) 243909 scan_4.0 1e5df418 Y------ 1312 1e5df418 cond wait(await_MC4) 243910 scan_5.0 1e5dfc98 Y------ 1312 1e5dfc98 cond wait(await_MC5) Memory pools count 1 name class addr totalsize freesize #allocfrag #freefrag 1494 V 1e8a0018 237568 16896 514 7 name free used name free used overhead 0 120 scb 0 96 opentable 0 13920 filetable 0 3144 ru 0 224 log 0 12816 temprec 0 5736 ralloc 0 132184 gentcb 0 11032 ostcb 0 2016 sort 0 56 sqscb 0 7864 rdahead 0 1600 xchg_desc 0 3528 xchg_port 0 3624 xchg_packet 0 1376 xchg_group 0 360 xchg_priv 0 400 hashfiletab 0 1680 osenv 0 1944 buft_buffer 0 8544 sqtcb 0 7240 fragman 0 512 shmblklist 0 656 Sess SQL Current Iso Lock SQL ISAM F.E. Id Stmt type Database Lvl Mode ERR ERR Vers 1494 SELECT INTO bir10ifx NL Not Wait 0 0 7.23 Current SQL statement : Current SQL statement : select unique a.sys_orig_stn_id[1,3]||'-'||a.sys_dest_stn_id[1,3] bdstn, b.stn_supercity_cd start_sstn, c.stn_supercity_cd end_sstn from stgt01_tiiss a, bir10t02_dorigsta b, bir10t02_dorigsta c where b.stn_cd= a.sys_orig_stn_id and c.stn_cd = a.sys_dest_stn_id and b.end_eftv_dt is null and c.end_eftv_dt is null and a.sys_orig_stn_id[1,3] <= a.sys_dest_stn_id[1,3] into temp sstmp1 Last parsed SQL statement : select unique a.sys_orig_stn_id[1,3]||'-'||a.sys_dest_stn_id[1,3] bdstn, b.stn_supercity_cd start_sstn, c.stn_supercity_cd end_sstn from stgt01_tiiss a, bir10t02_dorigsta b, bir10t02_dorigsta c where b.stn_cd= a.sys_orig_stn_id and c.stn_cd = a.sys_dest_stn_id and b.end_eftv_dt is null and c.end_eftv_dt is null and a.sys_orig_stn_id[1,3] <= a.sys_dest_stn_id[1,3] into temp sstmp1