On Wed, Nov 16, 2016 at 11:45 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> The header comment for heap_create_init_fork() says this:
>
> /*
> * Set up an init fork for an unlogged table so that it can be correctly
> * reinitialized on restart. Since we're going to do an immediate sync, we
> * only need to xlog this if archiving or streaming is enabled. And the
> * immediate sync is required, because otherwise there's no guarantee that
> * this will hit the disk before the next checkpoint moves the redo pointer.
> */
>
> Your patch causes the code not to match the comment any more. And the
> comment explains why at the time I wrote this code I thought it was OK
> to have the XLogIsNeeded() test in there, so it clearly needs
> updating.
Indeed I missed this comment block. Please let me suggest the following instead:
/*
* Set up an init fork for an unlogged table so that it can be correctly
- * reinitialized on restart. Since we're going to do an immediate sync, we
- * only need to xlog this if archiving or streaming is enabled. And the
- * immediate sync is required, because otherwise there's no guarantee that
- * this will hit the disk before the next checkpoint moves the redo pointer.
+ * reinitialized on restart. An immediate sync is required even if the
+ * page has been logged, because the write did not go through
+ * shared_buffers and therefore a concurrent checkpoint may have moved
+ * the redo pointer past our xlog record.
*/
--
Michael
