Add SKIP_LOCKED option to RangeVarGetRelidExtended().

This will be used for VACUUM (SKIP LOCKED).

Author: Nathan Bossart
Reviewed-By: Michael Paquier and Andres Freund
Discussion: https://postgr.es/m/20180306005349.b65whmvj7z6hbe2y@alap3.anarazel.de

diff --git a/src/backend/catalog/namespace.c b/src/backend/catalog/namespace.c
index 687d31e083ba511b084374493211fd4ea4e56836..d69b015c6980089a2d37b51bfc7bd6665cddb768 100644 (file)
--- a/src/backend/catalog/namespace.c
+++ b/src/backend/catalog/namespace.c
@@ -212,6 +212,15 @@ static bool MatchNamedCall(HeapTuple proctup, int nargs, List *argnames,
  * If flags contains RVR_NOWAIT, throw an error if we'd have to wait for a
  * lock.
  *
+ * If flags contains RVR_SKIP_LOCKED, return InvalidOid if we'd have to wait
+ * for a lock.
+ *
+ * flags cannot contain both RVR_NOWAIT and RVR_SKIP_LOCKED.
+ *
+ * Note that if RVR_MISSING_OK and RVR_SKIP_LOCKED are both specified, a
+ * return value of InvalidOid could either mean the relation is missing or it
+ * could not be locked.
+ *
  * Callback allows caller to check permissions or acquire additional locks
  * prior to grabbing the relation lock.
  */
@@ -226,6 +235,9 @@ RangeVarGetRelidExtended(const RangeVar *relation, LOCKMODE lockmode,
    bool        retry = false;
    bool        missing_ok = (flags & RVR_MISSING_OK) != 0;
 
+   /* verify that flags do no conflict */
+   Assert(!((flags & RVR_NOWAIT) && (flags & RVR_SKIP_LOCKED)));
+
    /*
     * We check the catalog name and then ignore it.
     */
@@ -363,20 +375,24 @@ RangeVarGetRelidExtended(const RangeVar *relation, LOCKMODE lockmode,
         */
        if (!OidIsValid(relId))
            AcceptInvalidationMessages();
-       else if (!(flags & RVR_NOWAIT))
+       else if (!(flags & (RVR_NOWAIT | RVR_SKIP_LOCKED)))
            LockRelationOid(relId, lockmode);
        else if (!ConditionalLockRelationOid(relId, lockmode))
        {
+           int         elevel = (flags & RVR_SKIP_LOCKED) ? DEBUG1 : ERROR;
+
            if (relation->schemaname)
-               ereport(ERROR,
+               ereport(elevel,
                        (errcode(ERRCODE_LOCK_NOT_AVAILABLE),
                         errmsg("could not obtain lock on relation \"%s.%s\"",
                                relation->schemaname, relation->relname)));
            else
-               ereport(ERROR,
+               ereport(elevel,
                        (errcode(ERRCODE_LOCK_NOT_AVAILABLE),
                         errmsg("could not obtain lock on relation \"%s\"",
                                relation->relname)));
+
+           return InvalidOid;
        }
 
        /*

diff --git a/src/include/catalog/namespace.h b/src/include/catalog/namespace.h
index 0bccf910a9ec50dbb726097d2682a384de6ecf4d..7991de5e210bb5800fb652d5350b914cecf48f52 100644 (file)
--- a/src/include/catalog/namespace.h
+++ b/src/include/catalog/namespace.h
@@ -53,7 +53,8 @@ typedef struct OverrideSearchPath
 typedef enum RVROption
 {
    RVR_MISSING_OK = 1 << 0,    /* don't error if relation doesn't exist */
-   RVR_NOWAIT = 1 << 1         /* error if relation cannot be locked */
+   RVR_NOWAIT = 1 << 1,        /* error if relation cannot be locked */
+   RVR_SKIP_LOCKED = 1 << 2    /* skip if relation cannot be locked */
 } RVROption;
 
 typedef void (*RangeVarGetRelidCallback) (const RangeVar *relation, Oid relId,