Make TRUNCATE do truncate-in-place when processing a relation that was created

or previously truncated in the current (sub)transaction.  This is safe since
if the (sub)transaction later rolls back, we'd just discard the rel's current
physical file anyway.  This avoids unreasonable growth in the number of
transient files when a relation is repeatedly truncated.  Per a performance
gripe a couple weeks ago from Todd Cook.

diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
index 3c0133bcbd70f375fb157304313523fa5f96fc29..ae406ae6abb9972a7a823408888344e21159500d 100644 (file)
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -2342,18 +2342,9 @@ heap_truncate(List *relids)
        {
                Oid                     rid = lfirst_oid(cell);
                Relation        rel;
-               Oid                     toastrelid;
 
                rel = heap_open(rid, AccessExclusiveLock);
                relations = lappend(relations, rel);
-
-               /* If there is a toast table, add it to the list too */
-               toastrelid = rel->rd_rel->reltoastrelid;
-               if (OidIsValid(toastrelid))
-               {
-                       rel = heap_open(toastrelid, AccessExclusiveLock);
-                       relations = lappend(relations, rel);
-               }
        }
 
        /* Don't allow truncate on tables that are referenced by foreign keys */
@@ -2364,19 +2355,47 @@ heap_truncate(List *relids)
        {
                Relation        rel = lfirst(cell);
 
-               /* Truncate the actual file (and discard buffers) */
-               RelationTruncate(rel, 0);
+               /* Truncate the relation */
+               heap_truncate_one_rel(rel);
 
-               /* If this relation has indexes, truncate the indexes too */
-               RelationTruncateIndexes(rel);
-
-               /*
-                * Close the relation, but keep exclusive lock on it until commit.
-                */
+               /* Close the relation, but keep exclusive lock on it until commit */
                heap_close(rel, NoLock);
        }
 }
 
+/*
+ *      heap_truncate_one_rel
+ *
+ *      This routine deletes all data within the specified relation.
+ *
+ * This is not transaction-safe, because the truncation is done immediately
+ * and cannot be rolled back later.  Caller is responsible for having
+ * checked permissions etc, and must have obtained AccessExclusiveLock.
+ */
+void
+heap_truncate_one_rel(Relation rel)
+{
+       Oid                     toastrelid;
+
+       /* Truncate the actual file (and discard buffers) */
+       RelationTruncate(rel, 0);
+
+       /* If the relation has indexes, truncate the indexes too */
+       RelationTruncateIndexes(rel);
+
+       /* If there is a toast table, truncate that too */
+       toastrelid = rel->rd_rel->reltoastrelid;
+       if (OidIsValid(toastrelid))
+       {
+               Relation        toastrel = heap_open(toastrelid, AccessExclusiveLock);
+
+               RelationTruncate(toastrel, 0);
+               RelationTruncateIndexes(toastrel);
+               /* keep the lock... */
+               heap_close(toastrel, NoLock);
+       }
+}
+
 /*
  * heap_truncate_check_FKs
  *             Check for foreign keys referencing a list of relations that

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 7029c3c1e8cd3b98e9d103c77f7c57dab88a3ec1..89dd19b2649c743d33e4bc46150d1bdcbf8dee8b 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -775,6 +775,7 @@ ExecuteTruncate(TruncateStmt *stmt)
        EState     *estate;
        ResultRelInfo *resultRelInfos;
        ResultRelInfo *resultRelInfo;
+       SubTransactionId mySubid;
        ListCell   *cell;
 
        /*
@@ -944,36 +945,58 @@ ExecuteTruncate(TruncateStmt *stmt)
        /*
         * OK, truncate each table.
         */
+       mySubid = GetCurrentSubTransactionId();
+
        foreach(cell, rels)
        {
                Relation        rel = (Relation) lfirst(cell);
-               Oid                     heap_relid;
-               Oid                     toast_relid;
 
                /*
-                * Create a new empty storage file for the relation, and assign it as
-                * the relfilenode value.       The old storage file is scheduled for
-                * deletion at commit.
+                * Normally, we need a transaction-safe truncation here.  However,
+                * if the table was either created in the current (sub)transaction
+                * or has a new relfilenode in the current (sub)transaction, then
+                * we can just truncate it in-place, because a rollback would
+                * cause the whole table or the current physical file to be
+                * thrown away anyway.
                 */
-               setNewRelfilenode(rel, RecentXmin);
-
-               heap_relid = RelationGetRelid(rel);
-               toast_relid = rel->rd_rel->reltoastrelid;
-
-               /*
-                * The same for the toast table, if any.
-                */
-               if (OidIsValid(toast_relid))
+               if (rel->rd_createSubid == mySubid ||
+                       rel->rd_newRelfilenodeSubid == mySubid)
                {
-                       rel = relation_open(toast_relid, AccessExclusiveLock);
-                       setNewRelfilenode(rel, RecentXmin);
-                       heap_close(rel, NoLock);
+                       /* Immediate, non-rollbackable truncation is OK */
+                       heap_truncate_one_rel(rel);
                }
+               else
+               {
+                       Oid                     heap_relid;
+                       Oid                     toast_relid;
 
-               /*
-                * Reconstruct the indexes to match, and we're done.
-                */
-               reindex_relation(heap_relid, true);
+                       /*
+                        * Need the full transaction-safe pushups.
+                        *
+                        * Create a new empty storage file for the relation, and assign it
+                        * as the relfilenode value. The old storage file is scheduled for
+                        * deletion at commit.
+                        */
+                       setNewRelfilenode(rel, RecentXmin);
+
+                       heap_relid = RelationGetRelid(rel);
+                       toast_relid = rel->rd_rel->reltoastrelid;
+
+                       /*
+                        * The same for the toast table, if any.
+                        */
+                       if (OidIsValid(toast_relid))
+                       {
+                               rel = relation_open(toast_relid, AccessExclusiveLock);
+                               setNewRelfilenode(rel, RecentXmin);
+                               heap_close(rel, NoLock);
+                       }
+
+                       /*
+                        * Reconstruct the indexes to match, and we're done.
+                        */
+                       reindex_relation(heap_relid, true);
+               }
        }
 
        /*

diff --git a/src/include/catalog/heap.h b/src/include/catalog/heap.h
index d618319e98b6938a47fabb8bfa37b502acb12508..d7fdc9b1f930bf15a72326b17e301f961420cd78 100644 (file)
--- a/src/include/catalog/heap.h
+++ b/src/include/catalog/heap.h
@@ -62,6 +62,8 @@ extern void heap_drop_with_catalog(Oid relid);
 
 extern void heap_truncate(List *relids);
 
+extern void heap_truncate_one_rel(Relation rel);
+
 extern void heap_truncate_check_FKs(List *relations, bool tempTables);
 
 extern List *heap_truncate_find_FKs(List *relationIds);