Cache counter values, avoiding I/O when it doesn't change.

This improves merge times by up to 25%, since looping over the vardb for
each package install is slow.

TEST=Emerge a bunch of packages, notice 25% speed improvement.
BUG=chromium-os:15112

Change-Id: I51dd617219cd1820ceeb702291bd790990995be4

diff --git a/pym/portage/dbapi/vartree.py b/pym/portage/dbapi/vartree.py
index 1302556fc2ec9d413bf0147dafa52714e63d40e1..a1299738963f34b6ba44c5e6a2a2c43270eaf569 100644 (file)
--- a/pym/portage/dbapi/vartree.py
+++ b/pym/portage/dbapi/vartree.py
@@ -158,6 +158,8 @@ class vardbapi(dbapi):
                        self._linkmap = LinkageMap(self)
                self._owners = self._owners_db(self)
 
+               self._cached_counter = None
+
        def getpath(self, mykey, filename=None):
                # This is an optimized hotspot, so don't use unicode-wrapped
                # os module and don't use os.path.join().
@@ -715,17 +717,6 @@ class vardbapi(dbapi):
                @param myroot: ignored, self._eroot is used instead
                """
                myroot = None
-               cp_list = self.cp_list
-               max_counter = 0
-               for cp in self.cp_all():
-                       for cpv in cp_list(cp):
-                               try:
-                                       counter = int(self.aux_get(cpv, ["COUNTER"])[0])
-                               except (KeyError, OverflowError, ValueError):
-                                       continue
-                               if counter > max_counter:
-                                       max_counter = counter
-
                new_vdb = False
                counter = -1
                try:
@@ -753,16 +744,27 @@ class vardbapi(dbapi):
                                writemsg("!!! %s\n" % str(e), noiselevel=-1)
                                del e
 
-               # We must ensure that we return a counter
-               # value that is at least as large as the
-               # highest one from the installed packages,
-               # since having a corrupt value that is too low
-               # can trigger incorrect AUTOCLEAN behavior due
-               # to newly installed packages having lower
-               # COUNTERs than the previous version in the
-               # same slot.
-               if counter > max_counter:
+               if self._cached_counter == counter:
+                       max_counter = counter
+               else:
+                       # We must ensure that we return a counter
+                       # value that is at least as large as the
+                       # highest one from the installed packages,
+                       # since having a corrupt value that is too low
+                       # can trigger incorrect AUTOCLEAN behavior due
+                       # to newly installed packages having lower
+                       # COUNTERs than the previous version in the
+                       # same slot.
+                       cp_list = self.cp_list
                        max_counter = counter
+                       for cp in self.cp_all():
+                               for cpv in cp_list(cp):
+                                       try:
+                                               pkg_counter = int(self.aux_get(cpv, ["COUNTER"])[0])
+                                       except (KeyError, OverflowError, ValueError):
+                                               continue
+                                       if pkg_counter > max_counter:
+                                               max_counter = pkg_counter
 
                if counter < 0 and not new_vdb:
                        writemsg(_("!!! Initializing COUNTER to " \
@@ -780,18 +782,19 @@ class vardbapi(dbapi):
                """
                myroot = None
                mycpv = None
-
                self.lock()
                try:
                        counter = self.get_counter_tick_core() - 1
-                       if incrementing:
-                               #increment counter
-                               counter += 1
-                               # use same permissions as config._init_dirs()
-                               ensure_dirs(os.path.dirname(self._counter_path),
-                                       gid=portage_gid, mode=0o2750, mask=0o2)
-                               # update new global counter file
-                               write_atomic(self._counter_path, str(counter))
+                       if self._cached_counter != counter:
+                               if incrementing:
+                                       #increment counter
+                                       counter += 1
+                                       # use same permissions as config._init_dirs()
+                                       ensure_dirs(os.path.dirname(self._counter_path),
+                                               gid=portage_gid, mode=0o2750, mask=0o2)
+                                       # update new global counter file
+                                       write_atomic(self._counter_path, str(counter))
+                               self._cached_counter = counter
                finally:
                        self.unlock()
 
@@ -2824,7 +2827,7 @@ class dblink(object):
                        env=env)
 
        def treewalk(self, srcroot, destroot, inforoot, myebuild, cleanup=0,
-               mydbapi=None, prev_mtimes=None):
+               mydbapi=None, prev_mtimes=None, counter=None):
                """
                
                This function does the following:
@@ -3242,7 +3245,8 @@ class dblink(object):
                        self.copyfile(inforoot+"/"+x)
 
                # write local package counter for recording
-               counter = self.vartree.dbapi.counter_tick(mycpv=self.mycpv)
+               if counter is not None:
+                       counter = self.vartree.dbapi.counter_tick(mycpv=self.mycpv)
                codecs.open(_unicode_encode(os.path.join(self.dbtmpdir, 'COUNTER'),
                        encoding=_encodings['fs'], errors='strict'),
                        'w', encoding=_encodings['repo.content'], errors='backslashreplace'
@@ -3857,7 +3861,7 @@ class dblink(object):
                                showMessage(zing + " " + mydest + "\n")
 
        def merge(self, mergeroot, inforoot, myroot=None, myebuild=None, cleanup=0,
-               mydbapi=None, prev_mtimes=None):
+               mydbapi=None, prev_mtimes=None, counter=None):
                """
                If portage is reinstalling itself, create temporary
                copies of PORTAGE_BIN_PATH and PORTAGE_PYM_PATH in order
@@ -3926,7 +3930,8 @@ class dblink(object):
                self.vartree.dbapi._bump_mtime(self.mycpv)
                try:
                        retval = self.treewalk(mergeroot, myroot, inforoot, myebuild,
-                               cleanup=cleanup, mydbapi=mydbapi, prev_mtimes=prev_mtimes)
+                               cleanup=cleanup, mydbapi=mydbapi, prev_mtimes=prev_mtimes,
+                               counter=counter)
 
                        # If PORTAGE_BUILDDIR doesn't exist, then it probably means
                        # fail-clean is enabled, and the success/die hooks have