donau

Donation authority for GNU Taler (experimental)
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commit.c (3426B)

      1 /*
      2    This file is part of TALER
      3    Copyright (C) 2024 Taler Systems SA
      4 
      5    TALER is free software; you can redistribute it and/or modify it under the
      6    terms of the GNU General Public License as published by the Free Software
      7    Foundation; either version 3, or (at your option) any later version.
      8 
      9    TALER is distributed in the hope that it will be useful, but WITHOUT ANY
     10    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
     11    A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
     12 
     13    You should have received a copy of the GNU General Public License along with
     14    TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
     15  */
     16 /**
     17  * @file src/donaudb/commit.c
     18  * @brief Implementation of the commit function for Postgres
     19  * @author Christian Grothoff
     20  */
     21 #include <donau_config.h>
     22 #include "commit.h"
     23 #include "helper.h"
     24 
     25 
     26 /**
     27  * Commit the current transaction of a database connection.
     28  *
     29  * @param ctx the `struct DONAUDB_PostgresContext` with the plugin-specific state
     30  * @return final transaction status
     31  */
     32 enum GNUNET_DB_QueryStatus
     33 DONAUDB_commit (struct DONAUDB_PostgresContext *ctx)
     34 {
     35   struct GNUNET_PQ_QueryParam params[] = {
     36     GNUNET_PQ_query_param_end
     37   };
     38   enum GNUNET_DB_QueryStatus qs;
     39 
     40   GNUNET_break (NULL != ctx->transaction_name);
     41   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
     42               "Committing transaction `%s'\n",
     43               ctx->transaction_name);
     44   PREPARE (ctx,
     45            "commit",
     46            "COMMIT");
     47 
     48   {
     49     PGresult *result;
     50 
     51     result = GNUNET_PQ_exec_prepared (ctx->conn,
     52                                       "commit",
     53                                       params);
     54     qs = GNUNET_PQ_eval_result (ctx->conn,
     55                                 "commit",
     56                                 result);
     57     /* PostgreSQL accepts COMMIT on a transaction it has already aborted: it
     58        silently rolls the transaction back and answers PGRES_COMMAND_OK with the
     59        command tag ROLLBACK.  GNUNET_PQ_eval_result() cannot tell that apart from
     60        a real commit, so every caller took the success path for a transaction
     61        whose writes are gone.  Report it as a soft error instead: sessions run
     62        SERIALIZABLE, so the overwhelmingly likely cause is an unhandled
     63        40001/40P01 for which retrying is right; a caller with a retry loop gives
     64        up after MAX_RETRIES and fails visibly, one without fails immediately.
     65 
     66        The *success* path deliberately keeps returning exactly what
     67        GNUNET_PQ_eval_prepared_non_select() returned before.  That function is
     68        GNUNET_PQ_exec_prepared() + GNUNET_PQ_eval_result() plus a
     69        strtol(PQcmdTuples()) step that only runs when the status is already
     70        GNUNET_DB_STATUS_SUCCESS_NO_RESULTS, and PQcmdTuples() on a COMMIT command
     71        tag is the empty string -- so that step yields 0, which is
     72        GNUNET_DB_STATUS_SUCCESS_NO_RESULTS again. */
     73     if ( (0 <= qs) &&
     74          (NULL != result) &&
     75          (0 == strcmp ("ROLLBACK",
     76                        PQcmdStatus (result))) )
     77     {
     78       GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
     79                   "Transaction `%s' was rolled back by the database instead of committed; a previous statement must have failed without being handled\n",
     80                   ctx->transaction_name);
     81       qs = GNUNET_DB_STATUS_SOFT_ERROR;
     82     }
     83     PQclear (result);
     84   }
     85   ctx->transaction_name = NULL;
     86   return qs;
     87 }