[datastore] Fix #3743

This change adds support for key == NULL to the datastore plugins
and replaces the offset argument with a next_uid and random arguments to
increase performance in the key == NULL case.

With the offset argument a datastore plugin would have to count all
matching keys before fetching the key at the right offset, which would
iterate over the entire database in the case of key == NULL.

The offset argument was used in two ways: to iterate over a set of
matching values and to start iteration at a random matching value. The new API
seperates these into two arguments: if random is true it will return a
random matching value, otherwise next_uid can be set to uid + 1 to return the
next matching value.

The random argument was not added to get_zero_anonymity. This function
is used to periodically insert zero anonymity values into the DHT. I
don't think it's necessary to randomize this.

1 files changed, 12 insertions, 15 deletions

diff --git a/src/datastore/datastore_api.c b/src/datastore/datastore_api.c
index c677654aa..26e1e501d 100644
--- a/src/datastore/datastore_api.c
+++ b/src/datastore/datastore_api.c
@@ -1325,10 +1325,7 @@ GNUNET_DATASTORE_get_for_replication (struct GNUNET_DATASTORE_Handle *h,
  * Get a single zero-anonymity value from the datastore.
  *
  * @param h handle to the datastore
- * @param offset offset of the result (modulo num-results); set to
- *               a random 64-bit value initially; then increment by
- *               one each time; detect that all results have been found by uid
- *               being again the first uid ever returned.
+ * @param next_uid return the result with lowest uid >= next_uid
  * @param queue_priority ranking of this request in the priority queue
  * @param max_queue_size at what queue size should this request be dropped
  *        (if other requests of higher priority are in the queue)
@@ -1342,7 +1339,7 @@ GNUNET_DATASTORE_get_for_replication (struct GNUNET_DATASTORE_Handle *h,
  */
 struct GNUNET_DATASTORE_QueueEntry *
 GNUNET_DATASTORE_get_zero_anonymity (struct GNUNET_DATASTORE_Handle *h,
-                                     uint64_t offset,
+                                     uint64_t next_uid,
                                      unsigned int queue_priority,
                                      unsigned int max_queue_size,
                                      enum GNUNET_BLOCK_Type type,
@@ -1357,13 +1354,12 @@ GNUNET_DATASTORE_get_zero_anonymity (struct GNUNET_DATASTORE_Handle *h,
   GNUNET_assert (NULL != proc);
   GNUNET_assert (type != GNUNET_BLOCK_TYPE_ANY);
   LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Asked to get %llu-th zero-anonymity entry of type %d\n",
-       (unsigned long long) offset,
+       "Asked to get a zero-anonymity entry of type %d\n",
        type);
   env = GNUNET_MQ_msg (m,
                        GNUNET_MESSAGE_TYPE_DATASTORE_GET_ZERO_ANONYMITY);
   m->type = htonl ((uint32_t) type);
-  m->offset = GNUNET_htonll (offset);
+  m->next_uid = GNUNET_htonll (next_uid);
   qc.rc.proc = proc;
   qc.rc.proc_cls = proc_cls;
   qe = make_queue_entry (h,
@@ -1392,10 +1388,8 @@ GNUNET_DATASTORE_get_zero_anonymity (struct GNUNET_DATASTORE_Handle *h,
  * will only be called once.
  *
  * @param h handle to the datastore
- * @param offset offset of the result (modulo num-results); set to
- *               a random 64-bit value initially; then increment by
- *               one each time; detect that all results have been found by uid
- *               being again the first uid ever returned.
+ * @param next_uid return the result with lowest uid >= next_uid
+ * @param random if true, return a random result instead of using next_uid
  * @param key maybe NULL (to match all entries)
  * @param type desired type, 0 for any
  * @param queue_priority ranking of this request in the priority queue
@@ -1409,7 +1403,8 @@ GNUNET_DATASTORE_get_zero_anonymity (struct GNUNET_DATASTORE_Handle *h,
  */
 struct GNUNET_DATASTORE_QueueEntry *
 GNUNET_DATASTORE_get_key (struct GNUNET_DATASTORE_Handle *h,
-                          uint64_t offset,
+                          uint64_t next_uid,
+                          bool random,
                           const struct GNUNET_HashCode *key,
                           enum GNUNET_BLOCK_Type type,
                           unsigned int queue_priority,
@@ -1433,14 +1428,16 @@ GNUNET_DATASTORE_get_key (struct GNUNET_DATASTORE_Handle *h,
     env = GNUNET_MQ_msg (gm,
                          GNUNET_MESSAGE_TYPE_DATASTORE_GET);
     gm->type = htonl (type);
-    gm->offset = GNUNET_htonll (offset);
+    gm->next_uid = GNUNET_htonll (next_uid);
+    gm->random = random;
   }
   else
   {
     env = GNUNET_MQ_msg (gkm,
                          GNUNET_MESSAGE_TYPE_DATASTORE_GET_KEY);
     gkm->type = htonl (type);
-    gkm->offset = GNUNET_htonll (offset);
+    gkm->next_uid = GNUNET_htonll (next_uid);
+    gkm->random = random;
     gkm->key = *key;
   }
   qc.rc.proc = proc;