$cursor = $collection->find($query,array("UID"))->limit($limit_size);

When Use LoadRunner Run PHP Code(up here),System Memory Add over to 2.5GB,latest to crash!!

My Question: Why Query Opt use amount of Memory and not release?

Here is Stack Trace
--------------------------------------------------------------------------------------
Mon Aug 9 16:46:00 [conn79] got request after shutdown()
Mon Aug 9 16:46:00 [conn59] assertion 10000 out of memory BufBuilder ns:SearchDatabase1.BasiTable query:{ TIMS:

}
Mon Aug 9 16:46:00 Got signal: 11 (Segmentation fault).

Mon Aug 9 16:46:00 [conn73] got request after shutdown()
Mon Aug 9 16:46:00 [conn70] got request after shutdown()
Mon Aug 9 16:46:00 [conn76] got request after shutdown()
Mon Aug 9 16:46:00 [conn64] got request after shutdown()
Mon Aug 9 16:46:00 [conn91] got request after shutdown()
Mon Aug 9 16:46:00 Got signal: 11 (Segmentation fault).

Mon Aug 9 16:46:00 [conn59] ntoskip:0 ntoreturn:20
Mon Aug 9 16:46:00 Got signal: 11 (Segmentation fault).

Mon Aug 9 16:46:00 [conn86] got request after shutdown()
Mon Aug 9 16:46:00 [conn94] got request after shutdown()
Mon Aug 9 16:46:00 Got signal: 11 (Segmentation fault).

Mon Aug 9 16:46:00 [conn56] got request after shutdown()
Mon Aug 9 16:46:00 [conn54] got request after shutdown()
Mon Aug 9 16:46:00 Got signal: 11 (Segmentation fault).

Mon Aug 9 16:46:00 [conn62] got request after shutdown()
Mon Aug 9 16:46:00 Got signal: 11 (Segmentation fault).

Mon Aug 9 16:46:00 Backtrace:
0x8489262 0x895420 0x83a1439 0x838f80f 0x824fa4a 0x83924b0 0x8397428 0x839b25f 0x839c159 0x839cc6d 0x823a746 0x834ce26 0x8355c17 0x848a243 0x81c74e8 0x84a247d 0xc5473b 0xbd2cfe
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo10abruptQuitEi+0x3c2) [0x8489262]
[0x895420]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZNK5mongo10FieldRange10nontrivialEv+0x49) [0x83a1439]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZNK5mongo9QueryPlan9newCursorERKNS_7DiskLocEi+0x7cf) [0x838f80f]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo11UserQueryOp5_initEv+0x38a) [0x824fa4a]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo12QueryPlanSet6Runner6initOpERNS_7QueryOpE+0x110) [0x83924b0]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo12QueryPlanSet6Runner3runEv+0x2b8) [0x8397428]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo12QueryPlanSet5runOpERNS_7QueryOpE+0x4f) [0x839b25f]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo16MultiPlanScanner9runOpOnceERNS_7QueryOpE+0x59) [0x839c159]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo16MultiPlanScanner5runOpERNS_7QueryOpE+0x2d) [0x839cc6d]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(ZN5mongo8runQueryERNS_7MessageERNS_12QueryMessageERNS_5CurOpES1+0xde6) [0x823a746]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod [0x834ce26]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo16assembleResponseERNS_7MessageERNS_10DbResponseERKNS_8SockAddrE+0x1587) [0x8355c17]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo10connThreadEPNS_13MessagingPortE+0x313) [0x848a243]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5boost6detail11thread_dataINS_3_bi6bind_tIvPFvPN5mongo13MessagingPortEENS2_5list1INS2_5valueIS6_EEEEEEE3runEv+0x18) [0x81c74e8]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(thread_proxy+0x7d) [0x84a247d]
/lib/libpthread.so.0 [0xc5473b]
/lib/libc.so.6(clone+0x5e) [0xbd2cfe]

Mon Aug 9 16:46:00 Got signal: 11 (Segmentation fault).

Mon Aug 9 16:46:00 [conn66] got request after shutdown()
Mon Aug 9 16:46:00 Backtrace:
0x8489262 0x895420 0x83a1439 0x838f80f 0x824fa4a 0x83924b0 0x8397428 0x839b25f 0x839c159 0x839cc6d 0x823a746 0x834ce26 0x8355c17 0x848a243 0x81c74e8 0x84a247d 0xc5473b 0xbd2cfe
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo10abruptQuitEi+0x3c2) [0x8489262]
[0x895420]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZNK5mongo10FieldRange10nontrivialEv+0x49) [0x83a1439]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZNK5mongo9QueryPlan9newCursorERKNS_7DiskLocEi+0x7cf) [0x838f80f]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo11UserQueryOp5_initEv+0x38a) [0x824fa4a]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo12QueryPlanSet6Runner6initOpERNS_7QueryOpE+0x110) [0x83924b0]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo12QueryPlanSet6Runner3runEv+0x2b8) [0x8397428]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo12QueryPlanSet5runOpERNS_7QueryOpE+0x4f) [0x839b25f]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo16MultiPlanScanner9runOpOnceERNS_7QueryOpE+0x59) [0x839c159]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo16MultiPlanScanner5runOpERNS_7QueryOpE+0x2d) [0x839cc6d]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(ZN5mongo8runQueryERNS_7MessageERNS_12QueryMessageERNS_5CurOpES1+0xde6) [0x823a746]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod [0x834ce26]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo16assembleResponseERNS_7MessageERNS_10DbResponseERKNS_8SockAddrE+0x1587) [0x8355c17]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5mongo10connThreadEPNS_13MessagingPortE+0x313) [0x848a243]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(_ZN5boost6detail11thread_dataINS_3_bi6bind_tIvPFvPN5mongo13MessagingPortEENS2_5list1INS2_5valueIS6_EEEEEEE3runEv+0x18) [0x81c74e8]
/91u/lib_install/mongodb/mongodb-linux-i686-1.6.0/bin/mongod(thread_proxy+0x7d) [0x84a247d]
/lib/libpthread.so.0 [0xc5473b]
/lib/libc.so.6(clone+0x5e) [0xbd2cfe]