Hi Amit,
>>> +
>>> + /* 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)
>>
>> That is because UNUSED page is as good as an empty page except that
>> empty page doesn't have any pagetype. If we add condition for checking
>> UNUSED page in above if check it will never show unused page as an
>> unsed page rather it will always show it as an empty page.
>>
>
> Oh, okay, but my main objection was that we should not check hash page
> type (hasho_flag) without ensuring whether it is a hash page. Can you
> try to adjust the above code so that this check can be moved after
> hasho_page_id check?
Yes, I got your point. I have done that but then i had to remove the
check for PageIsEmpty(). Anyways, I think PageIsEmpty() condition will
only be true for one page in entire hash index table and can be
ignored. If you wish, I could mention about it in the documentation.
>
>> To avoid
>> this, at the start of verify_hash_page function itself if we recognise
>> page as UNUSED page we return immediately.
>>
>>>
>>> 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?
>>
>> I think we should show separate message because they are two different
>> type of pages. In the sense like, one is initialised whereas other is
>> completely zero.
>>
>
> I understand your point, but not sure if it makes any difference to user.
>
okay, I have now anyways removed the check for PageIsEmpty. Please
refer to the attached '0002
allow_pageinspect_handle_UNUSED_hash_pages.patch'
Also, I have attached
'0001-Mark-freed-overflow-page-as-UNUSED-pagetype-v2.patch' that
handles your comment mentioned in [1].
[1] -
https://www.postgresql.org/message-id/CAA4eK1%2BVE_TDRLWpyeOf%2B7%2B6if68kgPNwO4guKo060rm_t3O5w%40mail.gmail.com
--
With Regards,
Ashutosh Sharma
EnterpriseDB:http://www.enterprisedb.com
From 86eb711ea80b495c9d2f5228558682d0e95c41eb Mon Sep 17 00:00:00 2001
From: ashu <ashu@localhost.localdomain>
Date: Thu, 23 Mar 2017 16:47:17 +0530
Subject: [PATCH] Mark freed overflow page as UNUSED pagetype v2
---
src/backend/access/hash/hash_xlog.c | 9 +++++++++
src/backend/access/hash/hashovfl.c | 13 ++++++++++++-
2 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/src/backend/access/hash/hash_xlog.c b/src/backend/access/hash/hash_xlog.c
index d9ac42c..2ccaf46 100644
--- a/src/backend/access/hash/hash_xlog.c
+++ b/src/backend/access/hash/hash_xlog.c
@@ -697,11 +697,20 @@ hash_xlog_squeeze_page(XLogReaderState *record)
if (XLogReadBufferForRedo(record, 2, &ovflbuf) == BLK_NEEDS_REDO)
{
Page ovflpage;
+ HashPageOpaque ovflopaque;
ovflpage = BufferGetPage(ovflbuf);
_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;
+
PageSetLSN(ovflpage, lsn);
MarkBufferDirty(ovflbuf);
}
diff --git a/src/backend/access/hash/hashovfl.c b/src/backend/access/hash/hashovfl.c
index a3cae21..d3eaee0 100644
--- a/src/backend/access/hash/hashovfl.c
+++ b/src/backend/access/hash/hashovfl.c
@@ -591,9 +591,20 @@ _hash_freeovflpage(Relation rel, Buffer bucketbuf, Buffer ovflbuf,
/*
* Initialize the freed overflow page. Just zeroing the page won't work,
* because WAL replay routines expect pages to be initialized. See
- * explanation of RBM_NORMAL mode atop XLogReadBufferExtended.
+ * explanation of RBM_NORMAL mode atop XLogReadBufferExtended. Also, mark
+ * the page as UNUSED type and retain it's page id. This allows the tools
+ * like pageinspect to consider it as a hash 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;
+
MarkBufferDirty(ovflbuf);
if (BufferIsValid(prevbuf))
--
1.8.3.1
diff --git a/contrib/pageinspect/hashfuncs.c b/contrib/pageinspect/hashfuncs.c
index 812a03f..6ba8847 100644
--- a/contrib/pageinspect/hashfuncs.c
+++ b/contrib/pageinspect/hashfuncs.c
@@ -70,6 +70,7 @@ verify_hash_page(bytea *raw_page, int flags)
errmsg("index table contains corrupted page")));
pageopaque = (HashPageOpaque) PageGetSpecialPointer(page);
+
if (pageopaque->hasho_page_id != HASHO_PAGE_ID)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
@@ -77,6 +78,10 @@ verify_hash_page(bytea *raw_page, int flags)
errdetail("Expected %08x, got %08x.",
HASHO_PAGE_ID, pageopaque->hasho_page_id)));
+ /* Check if it is an unused hash page. */
+ if (pageopaque->hasho_flag == LH_UNUSED_PAGE)
+ return page;
+
/* Check that page type is sane. */
pagetype = pageopaque->hasho_flag & LH_PAGE_TYPE;
if (pagetype != LH_OVERFLOW_PAGE && pagetype != LH_BUCKET_PAGE &&
--
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