access          various index access methods
access/common           common access routines
access/gist             easy-to-define access method system
access/hash             hash
access/heap             heap
access/index            index handling
access/nbtree           btree
access/rtree            rtree
access/transam          transaction manager (BEGIN/ABORT/COMMIT)
bootstrap       handles initdb requests to create initial template database
catalog         system catalog manipulation
commands        commands that do not require executor
executor        executes complex node plans from optimizer
include         include files
lib             support library
libpq           communication to client libpq library routines
main            passes control to postmaster or postgres
nodes           creation/manipulation of nodes
optimizer       creates path and plan
optimizer/path          creates path from parser output
optimizer/plan          optmizes path output
optimizer/prep          handle special plan cases
optimizer/util          optimizer support routines
parser          converts SQL query to query tree
postmaster      controls postgres server startup/termination
regex           regular expression library
rewrite         rules system
storage         manages various storage systems
storage/buffer          shared buffer pool manager
storage/file            file manager
storage/ipc             semaphores and shared memory
storage/large_object    large objects
storage/lmgr            lock manager
storage/page            page manager
storage/smgr            storage(disk) manager
tcop            traffic cop, dispatches request to proper module
tioga           array handling?
utils           support routines
utils/adt               built-in data type routines
utils/cache             system/relation/function cache routines
utils/error             error reporting routines
utils/fmgr              function manager
utils/hash              hash routines for internal algorithms
utils/init              initialization stuff
utils/mmgr              memory manager(process-local memory)
utils/sort              sort routines for internal algorithms
utils/time              transaction time qualification routines