vacuumlo: Use a cursor to limit client-side memory usage.

This prevents the client from gobbling up too much memory when the
number of large objects to be removed is very large.

Andrew Dunstan, reviewed by Josh Kupershmidt

diff --git a/contrib/vacuumlo/vacuumlo.c b/contrib/vacuumlo/vacuumlo.c
index 70f7ea70ba08dc11eb1d037aabc2d18f75e49a32..134fd9d9c82d3bbb4663a51cf3b88ea42d765834 100644 (file)
--- a/contrib/vacuumlo/vacuumlo.c
+++ b/contrib/vacuumlo/vacuumlo.c
@@ -290,74 +290,101 @@ vacuumlo(const char *database, const struct _param * param)
    PQclear(res);
 
    buf[0] = '\0';
-   strcat(buf, "SELECT lo FROM vacuum_l");
+   strcat(buf,
+          "DECLARE myportal CURSOR WITH HOLD FOR SELECT lo FROM vacuum_l");
    res = PQexec(conn, buf);
-   if (PQresultStatus(res) != PGRES_TUPLES_OK)
+   if (PQresultStatus(res) != PGRES_COMMAND_OK)
    {
-       fprintf(stderr, "Failed to read temp table:\n");
-       fprintf(stderr, "%s", PQerrorMessage(conn));
+       fprintf(stderr, "DECLARE CURSOR failed: %s", PQerrorMessage(conn));
        PQclear(res);
        PQfinish(conn);
        return -1;
    }
+   PQclear(res);
+
+   snprintf(buf, BUFSIZE, "FETCH FORWARD %ld IN myportal",
+            param->transaction_limit > 0 ? param->transaction_limit : 1000L);
 
-   matched = PQntuples(res);
    deleted = 0;
-   for (i = 0; i < matched; i++)
+
+   while (1)
    {
-       Oid         lo = atooid(PQgetvalue(res, i, 0));
+       res = PQexec(conn, buf);
+       if (PQresultStatus(res) != PGRES_TUPLES_OK)
+       {
+           fprintf(stderr, "FETCH FORWARD failed: %s", PQerrorMessage(conn));
+           PQclear(res);
+           PQfinish(conn);
+           return -1;
+       }
 
-       if (param->verbose)
+       matched = PQntuples(res);
+       if (matched <= 0)
        {
-           fprintf(stdout, "\rRemoving lo %6u   ", lo);
-           fflush(stdout);
+           /* at end of resultset */
+           PQclear(res);
+           break;
        }
 
-       if (param->dry_run == 0)
+       for (i = 0; i < matched; i++)
        {
-           if (lo_unlink(conn, lo) < 0)
+           Oid         lo = atooid(PQgetvalue(res, i, 0));
+
+           if (param->verbose)
+           {
+               fprintf(stdout, "\rRemoving lo %6u   ", lo);
+               fflush(stdout);
+           }
+
+           if (param->dry_run == 0)
            {
-               fprintf(stderr, "\nFailed to remove lo %u: ", lo);
-               fprintf(stderr, "%s", PQerrorMessage(conn));
-               if (PQtransactionStatus(conn) == PQTRANS_INERROR)
+               if (lo_unlink(conn, lo) < 0)
                {
-                   success = false;
-                   break;
+                   fprintf(stderr, "\nFailed to remove lo %u: ", lo);
+                   fprintf(stderr, "%s", PQerrorMessage(conn));
+                   if (PQtransactionStatus(conn) == PQTRANS_INERROR)
+                   {
+                       success = false;
+                       PQclear(res);
+                       break;
+                   }
                }
+               else
+                   deleted++;
            }
            else
                deleted++;
-       }
-       else
-           deleted++;
-       if (param->transaction_limit > 0 &&
-           (deleted % param->transaction_limit) == 0)
-       {
-           res2 = PQexec(conn, "commit");
-           if (PQresultStatus(res2) != PGRES_COMMAND_OK)
+
+           if (param->transaction_limit > 0 &&
+               (deleted % param->transaction_limit) == 0)
            {
-               fprintf(stderr, "Failed to commit transaction:\n");
-               fprintf(stderr, "%s", PQerrorMessage(conn));
+               res2 = PQexec(conn, "commit");
+               if (PQresultStatus(res2) != PGRES_COMMAND_OK)
+               {
+                   fprintf(stderr, "Failed to commit transaction:\n");
+                   fprintf(stderr, "%s", PQerrorMessage(conn));
+                   PQclear(res2);
+                   PQclear(res);
+                   PQfinish(conn);
+                   return -1;
+               }
                PQclear(res2);
-               PQclear(res);
-               PQfinish(conn);
-               return -1;
-           }
-           PQclear(res2);
-           res2 = PQexec(conn, "begin");
-           if (PQresultStatus(res2) != PGRES_COMMAND_OK)
-           {
-               fprintf(stderr, "Failed to start transaction:\n");
-               fprintf(stderr, "%s", PQerrorMessage(conn));
+               res2 = PQexec(conn, "begin");
+               if (PQresultStatus(res2) != PGRES_COMMAND_OK)
+               {
+                   fprintf(stderr, "Failed to start transaction:\n");
+                   fprintf(stderr, "%s", PQerrorMessage(conn));
+                   PQclear(res2);
+                   PQclear(res);
+                   PQfinish(conn);
+                   return -1;
+               }
                PQclear(res2);
-               PQclear(res);
-               PQfinish(conn);
-               return -1;
            }
-           PQclear(res2);
        }
+
+       PQclear(res);
    }
-   PQclear(res);
 
    /*
     * That's all folks!