From fd9ba53c492835b52bd75a5ae113b7bcc81fe161 Mon Sep 17 00:00:00 2001
From: Christian Grothoff <christian@grothoff.org>
Date: Thu, 24 Feb 2022 13:53:09 +0100
Subject: make_coin_known can experience serialization failures, add retry
 logic

---
 src/exchange/taler-exchange-httpd_db.c      | 13 -------------
 src/exchange/taler-exchange-httpd_db.h      | 13 +++++++++++++
 src/exchange/taler-exchange-httpd_deposit.c | 24 ++++++++++++++++++------
 src/exchange/taler-exchange-httpd_melt.c    | 23 +++++++++++++++++------
 4 files changed, 48 insertions(+), 25 deletions(-)

diff --git a/src/exchange/taler-exchange-httpd_db.c b/src/exchange/taler-exchange-httpd_db.c
index f621d8c87..d383c471d 100644
--- a/src/exchange/taler-exchange-httpd_db.c
+++ b/src/exchange/taler-exchange-httpd_db.c
@@ -29,19 +29,6 @@
 #include "taler-exchange-httpd_responses.h"
 
 
-/**
- * How often should we retry a transaction before giving up
- * (for transactions resulting in serialization/dead locks only).
- *
- * The current value is likely too high for production. We might want to
- * benchmark good values once we have a good database setup.  The code is
- * expected to work correctly with any positive value, albeit inefficiently if
- * we too aggressively force clients to retry the HTTP request merely because
- * we have database serialization issues.
- */
-#define MAX_TRANSACTION_COMMIT_RETRIES 100
-
-
 enum GNUNET_DB_QueryStatus
 TEH_make_coin_known (const struct TALER_CoinPublicInfo *coin,
                      struct MHD_Connection *connection,
diff --git a/src/exchange/taler-exchange-httpd_db.h b/src/exchange/taler-exchange-httpd_db.h
index 7c954ffe1..bca97cf0a 100644
--- a/src/exchange/taler-exchange-httpd_db.h
+++ b/src/exchange/taler-exchange-httpd_db.h
@@ -27,6 +27,19 @@
 #include <gnunet/gnunet_mhd_compat.h>
 
 
+/**
+ * How often should we retry a transaction before giving up
+ * (for transactions resulting in serialization/dead locks only).
+ *
+ * The current value is likely too high for production. We might want to
+ * benchmark good values once we have a good database setup.  The code is
+ * expected to work correctly with any positive value, albeit inefficiently if
+ * we too aggressively force clients to retry the HTTP request merely because
+ * we have database serialization issues.
+ */
+#define MAX_TRANSACTION_COMMIT_RETRIES 100
+
+
 /**
  * Ensure coin is known in the database, and handle conflicts and errors.
  *
diff --git a/src/exchange/taler-exchange-httpd_deposit.c b/src/exchange/taler-exchange-httpd_deposit.c
index ea319f23a..66cbe04ca 100644
--- a/src/exchange/taler-exchange-httpd_deposit.c
+++ b/src/exchange/taler-exchange-httpd_deposit.c
@@ -442,12 +442,24 @@ TEH_handler_deposit (struct MHD_Connection *connection,
     enum GNUNET_DB_QueryStatus qs;
 
     /* make sure coin is 'known' in database */
-    qs = TEH_make_coin_known (&deposit.coin,
-                              connection,
-                              &dc.known_coin_id,
-                              &mhd_ret);
-    /* no transaction => no serialization failures should be possible */
-    GNUNET_break (GNUNET_DB_STATUS_SOFT_ERROR != qs);
+    for (unsigned int tries = 0; tries<MAX_TRANSACTION_COMMIT_RETRIES; tries++)
+    {
+      qs = TEH_make_coin_known (&deposit.coin,
+                                connection,
+                                &dc.known_coin_id,
+                                &mhd_ret);
+      /* no transaction => no serialization failures should be possible */
+      if (GNUNET_DB_STATUS_SOFT_ERROR != qs)
+        break;
+    }
+    if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
+    {
+      GNUNET_break (0);
+      return TALER_MHD_reply_with_error (connection,
+                                         MHD_HTTP_INTERNAL_SERVER_ERROR,
+                                         TALER_EC_GENERIC_DB_COMMIT_FAILED,
+                                         "make_coin_known");
+    }
     if (qs < 0)
       return mhd_ret;
   }
diff --git a/src/exchange/taler-exchange-httpd_melt.c b/src/exchange/taler-exchange-httpd_melt.c
index 049fd09a0..4db1b2469 100644
--- a/src/exchange/taler-exchange-httpd_melt.c
+++ b/src/exchange/taler-exchange-httpd_melt.c
@@ -237,12 +237,23 @@ database_melt (struct MHD_Connection *connection,
     MHD_RESULT mhd_ret = MHD_NO;
     enum GNUNET_DB_QueryStatus qs;
 
-    qs = TEH_make_coin_known (&rmc->refresh_session.coin,
-                              connection,
-                              &rmc->known_coin_id,
-                              &mhd_ret);
-    /* no transaction => no serialization failures should be possible */
-    GNUNET_break (GNUNET_DB_STATUS_SOFT_ERROR != qs);
+    for (unsigned int tries = 0; tries<MAX_TRANSACTION_COMMIT_RETRIES; tries++)
+    {
+      qs = TEH_make_coin_known (&rmc->refresh_session.coin,
+                                connection,
+                                &rmc->known_coin_id,
+                                &mhd_ret);
+      if (GNUNET_DB_STATUS_SOFT_ERROR != qs)
+        break;
+    }
+    if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
+    {
+      GNUNET_break (0);
+      return TALER_MHD_reply_with_error (connection,
+                                         MHD_HTTP_INTERNAL_SERVER_ERROR,
+                                         TALER_EC_GENERIC_DB_COMMIT_FAILED,
+                                         "make_coin_known");
+    }
     if (qs < 0)
       return mhd_ret;
   }
-- 
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