Avoid passing zero as a value for vacuum_cost_limit, because it's not a valid

value for the vacuum code.  Instead, make zero signify getting the value from a
higher level configuration facility, just like -1 in the original coding.  We
still document that -1 is the value that disables the feature, to avoid
confusing the user unnecessarily.

Reported by Galy Lee in <200705310914.l4V9E6JA094603@wwwmaster.postgresql.org>;
per subsequent discussion.

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index eeb568a3610449f92e1bb2352acc2160a10641ba..121c0c71ada3a726e88166bd9a5906747bcd799a 100644 (file)
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -1339,7 +1339,7 @@
    be used for this particular value.  Observe that the
    <structfield>vac_cost_delay</> variable inherits its default value from the
    <xref linkend="guc-autovacuum-vacuum-cost-delay"> configuration parameter,
-   or from <varname>vacuum_cost_delay</> if the former is set to a negative
+   or from <xref linkend="guc-vacuum-cost-delay"> if the former is set to a negative
    value.  The same applies to <structfield>vac_cost_limit</>.
    Also, autovacuum will ignore attempts to set a per-table
    <structfield>freeze_max_age</> larger than the system-wide setting (it can only be set

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index cd1c4bdcd947429f4242aad5798446115b667ed2..af6c0546d4f45b613ea2130f619f86b9d5575769 100644 (file)
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -1548,7 +1548,11 @@ static void
 autovac_balance_cost(void)
 {
        WorkerInfo      worker;
-       int         vac_cost_limit = (autovacuum_vac_cost_limit >= 0 ?
+       /*
+        * note: in cost_limit, zero also means use value from elsewhere, because
+        * zero is not a valid value.
+        */
+       int         vac_cost_limit = (autovacuum_vac_cost_limit > 0 ?
                                                                  autovacuum_vac_cost_limit : VacuumCostLimit);
        int         vac_cost_delay = (autovacuum_vac_cost_delay >= 0 ?
                                                                  autovacuum_vac_cost_delay : VacuumCostDelay);
@@ -2140,12 +2144,14 @@ table_recheck_autovac(Oid relid)
                 * there is a tuple in pg_autovacuum, use it; else, use the GUC
                 * defaults.  Note that the fields may contain "-1" (or indeed any
                 * negative value), which means use the GUC defaults for each setting.
+                * In cost_limit, the value 0 also means to use the value from
+                * elsewhere.
                 */
                if (avForm != NULL)
                {
-                       vac_cost_limit = (avForm->vac_cost_limit >= 0) ?
+                       vac_cost_limit = (avForm->vac_cost_limit > 0) ?
                                avForm->vac_cost_limit :
-                               ((autovacuum_vac_cost_limit >= 0) ?
+                               ((autovacuum_vac_cost_limit > 0) ?
                                 autovacuum_vac_cost_limit : VacuumCostLimit);
 
                        vac_cost_delay = (avForm->vac_cost_delay >= 0) ?
@@ -2158,7 +2164,7 @@ table_recheck_autovac(Oid relid)
                }
                else
                {
-                       vac_cost_limit = (autovacuum_vac_cost_limit >= 0) ?
+                       vac_cost_limit = (autovacuum_vac_cost_limit > 0) ?
                                autovacuum_vac_cost_limit : VacuumCostLimit;
 
                        vac_cost_delay = (autovacuum_vac_cost_delay >= 0) ?