Re: pageinspect and hash indexes

On Mon, Mar 20, 2017 at 6:53 PM, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com> wrote:
>
> I think it is not just happening for freed overflow but also for newly
> allocated bucket page. It would be good if we could mark freed
> overflow page as UNUSED page rather than just initialising it's header
> portion and leaving the page type in special area as it is. Attached
> is the patch '0001-mark_freed_ovflpage_as_UNUSED_pagetype.patch' that
> marks a freed overflow page as an unused page.
>

_hash_pageinit(ovflpage, BufferGetPageSize(ovflbuf));
+
+ ovflopaque = (HashPageOpaque) PageGetSpecialPointer(ovflpage);
+
+ ovflopaque->hasho_prevblkno = InvalidBlockNumber;
+ ovflopaque->hasho_nextblkno = InvalidBlockNumber;
+ ovflopaque->hasho_bucket = -1;
+ ovflopaque->hasho_flag = LH_UNUSED_PAGE;
+ ovflopaque->hasho_page_id = HASHO_PAGE_ID;
+

You need similar initialization in replay routine as well.

> Also, I have now changed pageinspect module to handle unused and empty
> hash index page. Attached is the patch
> (0002-allow_pageinspect_handle_UNUSED_OR_EMPTY_hash_pages.patch) for
> the same.
>

1.
@@ -70,6 +70,17 @@ verify_hash_page(bytea *raw_page, int flags)
pageopaque = (HashPageOpaque) PageGetSpecialPointer(page);
+
+ /* Check if it is an unused hash page. */
+ if (pageopaque->hasho_flag == LH_UNUSED_PAGE)
+ return page;

I don't see we need to have a separate check for unused page, why
can't it be checked with other page types in below check.

if (pagetype != LH_OVERFLOW_PAGE && pagetype != LH_BUCKET_PAGE &&
pagetype != LH_BITMAP_PAGE && pagetype != LH_META_PAGE)

2.
+ /* Check if it is an empty hash page. */
+ if (PageIsEmpty(page))
+ ereport(ERROR,
+ (errcode(ERRCODE_INDEX_CORRUPTED),
+ errmsg("index table contains empty page")));

Do we want to give a separate message for EMPTY and NEW pages? Isn't
it better that the same error message can be given for both of them as
from user perspective there is not much difference between both the
messages?

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com