From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Mon, 20 Apr 2015 13:47:58 +0000 (+0300)
Subject: Add comments
X-Git-Url: http://git.postgresql.org/gitweb/review?a=commitdiff_plain;h=a1f6bc8582240a7b7186f6055fcc434f82165e6d;p=users%2Fheikki%2Fpostgres.git

Add comments
---

diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index f68dd9034f..a2ad7a5bbf 100644
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -1018,7 +1018,14 @@ sequence_read_tuple(SequenceHandle *seqh)
 }
 
 /*
- * Update the page, optionally do WAL logging of the tuple
+ * Update a sequence tuple.
+ *
+ * If 'newtup' is valid, the tuple on the page is replaced with 'newtup'.
+ * Otherwise, the caller has modified the tuple directly on the page, and
+ * we just handle WAL-logging and dirtying the buffer here.
+ *
+ * If 'do_wal' is false, the update doesn't need to be WAL-logged. After
+ * a crash, you might get an old copy of the tuple.
  */
 void
 sequence_save_tuple(SequenceHandle *seqh, HeapTuple newtup, bool do_wal)
@@ -1046,12 +1053,12 @@ sequence_save_tuple(SequenceHandle *seqh, HeapTuple newtup, bool do_wal)
 	if (do_wal && RelationNeedsWAL(seqh->rel))
 		GetTopTransactionId();
 
+	/*
+	 * If the caller passed a new tuple, replace the old one with it.
+	 * Otherwise just mark the buffer dirty and WAL-log it.
+	 */
 	if (HeapTupleIsValid(newtup))
 	{
-		/*
-		 * New tuple was passed, we must process it and replace the old one on
-		 * the same page.
-		 */
 		Page	temppage;
 
 		/* Sequence tuples are always frozen. */
@@ -1062,9 +1069,7 @@ sequence_save_tuple(SequenceHandle *seqh, HeapTuple newtup, bool do_wal)
 		newtup->t_data->t_infomask |= HEAP_XMAX_INVALID;
 		ItemPointerSet(&newtup->t_data->t_ctid, 0, FirstOffsetNumber);
 
-		/*
-		 * Replace the original tuple on the page.
-		 */
+		/* Replace the original tuple on the page. */
 		temppage = PageGetTempPageCopySpecial(page);
 
 		if (PageAddItem(temppage, (Item) newtup->t_data, newtup->t_len,
@@ -1087,11 +1092,6 @@ sequence_save_tuple(SequenceHandle *seqh, HeapTuple newtup, bool do_wal)
 	}
 	else
 	{
-		/*
-		 * New tuple was not sent, so the original tuple was probably just
-		 * changed inline, all we need to do is mark the buffer dirty and
-		 * optionally log the updated tuple.
-		 */
 		START_CRIT_SECTION();
 
 		MarkBufferDirtyHint(seqh->buf, true);
@@ -1103,6 +1103,9 @@ sequence_save_tuple(SequenceHandle *seqh, HeapTuple newtup, bool do_wal)
 	}
 }
 
+/*
+ * Release a tuple, read with sequence_read_tuple, without saving it
+ */
 void
 sequence_release_tuple(SequenceHandle *seqh)
 {