Optimize recompression in ATRewriteTable()

Nikita Glukhov · Nikita Glukhov · commit 7ac1e2e2763f · 2017-05-02T21:38:26.000+03:00
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
@@ -2571,7 +2571,7 @@ heap_insert(Relation relation, HeapTuple tup, TupleDesc tupdesc,
 	return HeapTupleGetOid(tup);
 }
 
-static inline bool
+bool
 tuple_attr_compression_equals(TupleDesc td1, TupleDesc td2, AttrNumber attidx)
 {
 	if (td1->attrs[attidx]->attcompression !=
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
@@ -4554,6 +4554,7 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 		List	   *dropped_attrs = NIL;
 		ListCell   *lc;
 		Snapshot	snapshot;
+		bool	   *recompress;
 
 		if (newrel)
 			ereport(DEBUG1,
@@ -4602,6 +4603,22 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 				dropped_attrs = lappend_int(dropped_attrs, i);
 		}
 
+		if (tab->newvals != NIL)
+			recompress = NULL; /* recompress all */
+		else
+		{
+			int natts = Min(oldTupDesc->natts, newTupDesc->natts);
+
+			recompress = palloc0(sizeof(bool) * oldTupDesc->natts);
+
+			for (i = 0; i < natts; i++)
+				if (!tuple_attr_compression_equals(oldTupDesc, newTupDesc, i))
+					recompress[i] = true;
+
+			foreach(lc, dropped_attrs)
+				recompress[lfirst_int(lc)] = false;
+		}
+
 		/*
 		 * Scan through the rows, generating a new row if needed and then
 		 * checking all the constraints.
@@ -4622,7 +4639,8 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 				Oid			tupOid = InvalidOid;
 
 				/* Extract data from old tuple */
-				heap_deform_tuple(tuple, oldTupDesc, values, isnull);
+				heap_deform_tuple_decompress(tuple, oldTupDesc, values, isnull,
+											 recompress);
 				if (oldTupDesc->tdhasoid)
 					tupOid = HeapTupleGetOid(tuple);
 
@@ -4650,7 +4668,8 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 				 * Form the new tuple. Note that we don't explicitly pfree it,
 				 * since the per-tuple memory context will be reset shortly.
 				 */
-				tuple = heap_form_tuple(newTupDesc, values, isnull);
+				tuple = heap_form_tuple_compress(newTupDesc, values, isnull,
+												 recompress);
 
 				/* Preserve OID, if any */
 				if (newTupDesc->tdhasoid)
diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
@@ -181,6 +181,9 @@ extern void simple_heap_update(Relation relation, ItemPointer otid,
 extern void heap_sync(Relation relation);
 extern void heap_update_snapshot(HeapScanDesc scan, Snapshot snapshot);
 
+extern bool tuple_attr_compression_equals(TupleDesc td1, TupleDesc td2,
+										  AttrNumber attidx);
+
 /* in heap/pruneheap.c */
 extern void heap_page_prune_opt(Relation relation, Buffer buffer);
 extern int heap_page_prune(Relation relation, Buffer buffer,

Original file line number	Diff line number	Diff line change
`@@ -2571,7 +2571,7 @@ heap_insert(Relation relation, HeapTuple tup, TupleDesc tupdesc,`
`2571`	`2571`	`return HeapTupleGetOid(tup);`
`2572`	`2572`	`}`
`2573`	`2573`
`2574`		`-static inline bool`
	`2574`	`+bool`
`2575`	`2575`	`tuple_attr_compression_equals(TupleDesc td1, TupleDesc td2, AttrNumber attidx)`
`2576`	`2576`	`{`
`2577`	`2577`	`if (td1->attrs[attidx]->attcompression !=`