[GENERAL] how to set CACHEDEBUG ?

[sunpeng]

I noticed there is a piece of code:
#ifdef CACHEDEBUG
#define InitCatCache_DEBUG2 \
do { \
    elog(.......
} while(0)
#else
#define InitCatCache_DEBUG2
#endif

Now I'd like to set CACHEDEBUG, how to set up it ? where ?
thanks

peng