Add ability to limit the number of unclaimed build requests we query

for, and make getOldestRequestTime only request 1.

buildbot/db/connector.py

@@ -793,16 +793,19 @@ def _txn_get_buildername_for_brid(self, t, brid):
         return r[0][0]
 
     def get_unclaimed_buildrequests(self, buildername, old, master_name,
-                                    master_incarnation, t):
-        t.execute(self.quoteq("SELECT br.id"
-                              " FROM buildrequests AS br, buildsets AS bs"
-                              " WHERE br.buildername=? AND br.complete=0"
-                              " AND br.buildsetid=bs.id"
-                              " AND (br.claimed_at<?"
-                              "      OR (br.claimed_by_name=?"
-                              "          AND br.claimed_by_incarnation!=?))"
-                              " ORDER BY br.priority DESC,bs.submitted_at ASC"),
-                  (buildername, old, master_name, master_incarnation))
+                                    master_incarnation, t, limit=None):
+        q = ("SELECT br.id"
+             " FROM buildrequests AS br, buildsets AS bs"
+             " WHERE br.buildername=? AND br.complete=0"
+             " AND br.buildsetid=bs.id"
+             " AND (br.claimed_at<?"
+             "      OR (br.claimed_by_name=?"
+             "          AND br.claimed_by_incarnation!=?))"
+             " ORDER BY br.priority DESC,bs.submitted_at ASC")
+        if limit:
+            q += " LIMIT %s" % limit
+        t.execute(self.quoteq(q),
+                (buildername, old, master_name, master_incarnation))
         requests = [self.getBuildRequestWithNumber(brid, t)
                     for (brid,) in t.fetchall()]
         return requests

buildbot/process/builder.py

@@ -556,21 +556,22 @@ def _start_builds(self, assignments):
         self.updateBigStatus()
 
 
-    def getBuildable(self):
-        return self.db.runInteractionNow(self._getBuildable)
-    def _getBuildable(self, t):
+    def getBuildable(self, limit=None):
+        return self.db.runInteractionNow(self._getBuildable, limit)
+    def _getBuildable(self, t, limit):
         now = util.now()
         old = now - self.RECLAIM_INTERVAL
         return self.db.get_unclaimed_buildrequests(self.name, old,
                                                    self.master_name,
                                                    self.master_incarnation,
-                                                   t)
+                                                   t,
+                                                   limit)
 
     def getOldestRequestTime(self):
         """Returns the timestamp of the oldest build request for this builder.
 
         If there are no build requests, None is returned."""
-        buildable = self.getBuildable()
+        buildable = self.getBuildable(1)
         if buildable:
             # TODO: this is sorted by priority first, not strictly reqtime
             return buildable[0].getSubmitTime()