From ae8d481e1ce9f694a42619809d2c9b6e6acf3497 Mon Sep 17 00:00:00 2001
From: Christian Grothoff <christian@grothoff.org>
Date: Sun, 5 Sep 2021 15:25:46 +0200
Subject: implement taler-exchange-transfer DB sharding logic

---
 src/exchangedb/plugin_exchangedb_postgres.c | 123 +++++++++++++++++++++-------
 1 file changed, 94 insertions(+), 29 deletions(-)

(limited to 'src/exchangedb/plugin_exchangedb_postgres.c')

diff --git a/src/exchangedb/plugin_exchangedb_postgres.c b/src/exchangedb/plugin_exchangedb_postgres.c
index d66370a25..817c1a18c 100644
--- a/src/exchangedb/plugin_exchangedb_postgres.c
+++ b/src/exchangedb/plugin_exchangedb_postgres.c
@@ -1188,11 +1188,12 @@ prepare_statements (struct PostgresClosure *pg)
                             ",type"
                             ",buf"
                             " FROM prewire"
-                            " WHERE finished=FALSE"
+                            " WHERE prewire_uuid >= $1"
+                            "   AND finished=FALSE"
                             "   AND failed=FALSE"
                             " ORDER BY prewire_uuid ASC"
-                            " LIMIT 1;",
-                            0),
+                            " LIMIT $2;",
+                            2),
     /* Used in #postgres_select_deposits_missing_wire */
     GNUNET_PQ_make_prepare ("deposits_get_overdue",
                             "SELECT"
@@ -6984,52 +6985,116 @@ postgres_wire_prepare_data_mark_failed (
 }
 
 
+/**
+ * Closure for #prewire_cb().
+ */
+struct PrewireContext
+{
+  /**
+   * Function to call on each result.
+   */
+  TALER_EXCHANGEDB_WirePreparationIterator cb;
+
+  /**
+   * Closure for @a cb.
+   */
+  void *cb_cls;
+
+  /**
+   * #GNUNET_OK if everything went fine.
+   */
+  enum GNUNET_GenericReturnValue status;
+};
+
+
+/**
+ * Invoke the callback for each result.
+ *
+ * @param cls a `struct MissingWireContext *`
+ * @param result SQL result
+ * @param num_results number of rows in @a result
+ */
+static void
+prewire_cb (void *cls,
+            PGresult *result,
+            unsigned int num_results)
+{
+  struct PrewireContext *pc = cls;
+
+  for (unsigned int i = 0; i < num_results; i++)
+  {
+    uint64_t prewire_uuid;
+    char *type;
+    void *buf = NULL;
+    size_t buf_size;
+    struct GNUNET_PQ_ResultSpec rs[] = {
+      GNUNET_PQ_result_spec_uint64 ("prewire_uuid",
+                                    &prewire_uuid),
+      GNUNET_PQ_result_spec_string ("type",
+                                    &type),
+      GNUNET_PQ_result_spec_variable_size ("buf",
+                                           &buf,
+                                           &buf_size),
+      GNUNET_PQ_result_spec_end
+    };
+
+    if (GNUNET_OK !=
+        GNUNET_PQ_extract_result (result,
+                                  rs,
+                                  i))
+    {
+      GNUNET_break (0);
+      pc->status = GNUNET_SYSERR;
+      return;
+    }
+    pc->cb (pc->cb_cls,
+            prewire_uuid,
+            type,
+            buf,
+            buf_size);
+    GNUNET_PQ_cleanup_result (rs);
+  }
+}
+
+
 /**
  * Function called to get an unfinished wire transfer
  * preparation data. Fetches at most one item.
  *
  * @param cls closure
+ * @param start_row offset to query table at
+ * @param limit maximum number of results to return
  * @param cb function to call for ONE unfinished item
  * @param cb_cls closure for @a cb
  * @return transaction status code
  */
 static enum GNUNET_DB_QueryStatus
 postgres_wire_prepare_data_get (void *cls,
+                                uint64_t start_row,
+                                uint64_t limit,
                                 TALER_EXCHANGEDB_WirePreparationIterator cb,
                                 void *cb_cls)
 {
   struct PostgresClosure *pg = cls;
-  enum GNUNET_DB_QueryStatus qs;
   struct GNUNET_PQ_QueryParam params[] = {
+    GNUNET_PQ_query_param_uint64 (&start_row),
+    GNUNET_PQ_query_param_uint64 (&limit),
     GNUNET_PQ_query_param_end
   };
-  uint64_t prewire_uuid;
-  char *type;
-  void *buf = NULL;
-  size_t buf_size;
-  struct GNUNET_PQ_ResultSpec rs[] = {
-    GNUNET_PQ_result_spec_uint64 ("prewire_uuid",
-                                  &prewire_uuid),
-    GNUNET_PQ_result_spec_string ("type",
-                                  &type),
-    GNUNET_PQ_result_spec_variable_size ("buf",
-                                         &buf,
-                                         &buf_size),
-    GNUNET_PQ_result_spec_end
+  struct PrewireContext pc = {
+    .cb = cb,
+    .cb_cls = cb_cls,
+    .status = GNUNET_OK
   };
+  enum GNUNET_DB_QueryStatus qs;
 
-  qs = GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
-                                                 "wire_prepare_data_get",
-                                                 params,
-                                                 rs);
-  if (0 >= qs)
-    return qs;
-  cb (cb_cls,
-      prewire_uuid,
-      type,
-      buf,
-      buf_size);
-  GNUNET_PQ_cleanup_result (rs);
+  qs = GNUNET_PQ_eval_prepared_multi_select (pg->conn,
+                                             "wire_prepare_data_get",
+                                             params,
+                                             &prewire_cb,
+                                             &pc);
+  if (GNUNET_OK != pc.status)
+    return GNUNET_DB_STATUS_HARD_ERROR;
   return qs;
 }
 
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