Tom Lane wrote:
> Alvaro Herrera <alvhe...@2ndquadrant.com> writes:
> > typedef struct BrinSpecialSpace
> > {
> > char padding[MAXALIGN(1) - 2 * sizeof(uint16)];
> > uint16 flags;
> > uint16 type;
> > } BrinSpecialSpace;
>
> I should expect that to fail altogether on 32-bit machines, because
> the declared array size will be zero.
Hah, of course.
> You could try something like
>
> typedef struct BrinSpecialSpace
> {
> uint16 vector[MAXALIGN(1) / sizeof(uint16)];
> } BrinSpecialSpace;
>
> and then some access macros to use the last and next-to-last
> elements of that array.
Ah, thanks, that works fine on x86-64. Here's a patch I intend to push
tomorrow.
Heikki suggested that the comment above GinPageOpaqueData be moved to
some better place, but I couldn't find any such. If there are other
ideas, I'm all ears.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
commit 8532bfeffdaeffa1d49c390ba6b7b0b46a20afb7
Author: Alvaro Herrera <alvhe...@alvh.no-ip.org>
Date: Mon Mar 9 23:18:16 2015 -0300
Move BRIN page type to page's last two bytes
... which is the usual convention, so that pg_filedump and similar
utilities can tell apart pages of different AMs.
Per note from Heikki at
http://www.postgresql.org/message-id/546a16ef.9070...@vmware.com
diff --git a/contrib/pageinspect/brinfuncs.c b/contrib/pageinspect/brinfuncs.c
index 630dda4..1b15a7b 100644
--- a/contrib/pageinspect/brinfuncs.c
+++ b/contrib/pageinspect/brinfuncs.c
@@ -58,12 +58,9 @@ brin_page_type(PG_FUNCTION_ARGS)
{
bytea *raw_page = PG_GETARG_BYTEA_P(0);
Page page = VARDATA(raw_page);
- BrinSpecialSpace *special;
char *type;
- special = (BrinSpecialSpace *) PageGetSpecialPointer(page);
-
- switch (special->type)
+ switch (BrinPageType(page))
{
case BRIN_PAGETYPE_META:
type = "meta";
@@ -75,7 +72,7 @@ brin_page_type(PG_FUNCTION_ARGS)
type = "regular";
break;
default:
- type = psprintf("unknown (%02x)", special->type);
+ type = psprintf("unknown (%02x)", BrinPageType(page));
break;
}
@@ -91,7 +88,6 @@ verify_brin_page(bytea *raw_page, uint16 type, const char *strtype)
{
Page page;
int raw_page_size;
- BrinSpecialSpace *special;
raw_page_size = VARSIZE(raw_page) - VARHDRSZ;
@@ -104,13 +100,12 @@ verify_brin_page(bytea *raw_page, uint16 type, const char *strtype)
page = VARDATA(raw_page);
/* verify the special space says this page is what we want */
- special = (BrinSpecialSpace *) PageGetSpecialPointer(page);
- if (special->type != type)
+ if (BrinPageType(page) != type)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("page is not a BRIN page of type \"%s\"", strtype),
errdetail("Expected special type %08x, got %08x.",
- type, special->type)));
+ type, BrinPageType(page))));
return page;
}
diff --git a/src/backend/access/brin/brin_pageops.c b/src/backend/access/brin/brin_pageops.c
index 4e9392b..acb64bd 100644
--- a/src/backend/access/brin/brin_pageops.c
+++ b/src/backend/access/brin/brin_pageops.c
@@ -53,7 +53,6 @@ brin_doupdate(Relation idxrel, BlockNumber pagesPerRange,
BrinTuple *oldtup;
Size oldsz;
Buffer newbuf;
- BrinSpecialSpace *special;
bool extended = false;
newsz = MAXALIGN(newsz);
@@ -113,8 +112,6 @@ brin_doupdate(Relation idxrel, BlockNumber pagesPerRange,
return false;
}
- special = (BrinSpecialSpace *) PageGetSpecialPointer(oldpage);
-
/*
* Great, the old tuple is intact. We can proceed with the update.
*
@@ -124,7 +121,7 @@ brin_doupdate(Relation idxrel, BlockNumber pagesPerRange,
* caller told us there isn't, if a concurrent update moved another tuple
* elsewhere or replaced a tuple with a smaller one.
*/
- if (((special->flags & BRIN_EVACUATE_PAGE) == 0) &&
+ if (((BrinPageFlags(oldpage) & BRIN_EVACUATE_PAGE) == 0) &&
brin_can_do_samepage_update(oldbuf, origsz, newsz))
{
if (BufferIsValid(newbuf))
@@ -374,12 +371,9 @@ brin_doinsert(Relation idxrel, BlockNumber pagesPerRange,
void
brin_page_init(Page page, uint16 type)
{
- BrinSpecialSpace *special;
-
PageInit(page, BLCKSZ, sizeof(BrinSpecialSpace));
- special = (BrinSpecialSpace *) PageGetSpecialPointer(page);
- special->type = type;
+ BrinPageType(page) = type;
}
/*
@@ -420,7 +414,6 @@ brin_start_evacuating_page(Relation idxRel, Buffer buf)
{
OffsetNumber off;
OffsetNumber maxoff;
- BrinSpecialSpace *special;
Page page;
page = BufferGetPage(buf);
@@ -428,8 +421,6 @@ brin_start_evacuating_page(Relation idxRel, Buffer buf)
if (PageIsNew(page))
return false;
- special = (BrinSpecialSpace *) PageGetSpecialPointer(page);
-
maxoff = PageGetMaxOffsetNumber(page);
for (off = FirstOffsetNumber; off <= maxoff; off++)
{
@@ -439,7 +430,7 @@ brin_start_evacuating_page(Relation idxRel, Buffer buf)
if (ItemIdIsUsed(lp))
{
/* prevent other backends from adding more stuff to this page */
- special->flags |= BRIN_EVACUATE_PAGE;
+ BrinPageFlags(page) |= BRIN_EVACUATE_PAGE;
MarkBufferDirtyHint(buf, true);
return true;
@@ -463,8 +454,7 @@ brin_evacuate_page(Relation idxRel, BlockNumber pagesPerRange,
page = BufferGetPage(buf);
- Assert(((BrinSpecialSpace *)
- PageGetSpecialPointer(page))->flags & BRIN_EVACUATE_PAGE);
+ Assert(BrinPageFlags(page) & BRIN_EVACUATE_PAGE);
maxoff = PageGetMaxOffsetNumber(page);
for (off = FirstOffsetNumber; off <= maxoff; off++)
@@ -677,11 +667,8 @@ brin_getinsertbuffer(Relation irel, Buffer oldbuf, Size itemsz,
static Size
br_page_get_freespace(Page page)
{
- BrinSpecialSpace *special;
-
- special = (BrinSpecialSpace *) PageGetSpecialPointer(page);
if (!BRIN_IS_REGULAR_PAGE(page) ||
- (special->flags & BRIN_EVACUATE_PAGE) != 0)
+ (BrinPageFlags(page) & BRIN_EVACUATE_PAGE) != 0)
return 0;
else
return PageGetFreeSpace(page);
diff --git a/src/backend/access/brin/brin_revmap.c b/src/backend/access/brin/brin_revmap.c
index 5e4499d..80795ec 100644
--- a/src/backend/access/brin/brin_revmap.c
+++ b/src/backend/access/brin/brin_revmap.c
@@ -446,7 +446,7 @@ revmap_physical_extend(BrinRevmap *revmap)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("unexpected page type 0x%04X in BRIN index \"%s\" block %u",
- BRIN_PAGE_TYPE(page),
+ BrinPageType(page),
RelationGetRelationName(irel),
BufferGetBlockNumber(buf))));
diff --git a/src/include/access/brin_page.h b/src/include/access/brin_page.h
index 44ce5f6..6c645b3 100644
--- a/src/include/access/brin_page.h
+++ b/src/include/access/brin_page.h
@@ -20,24 +20,44 @@
#include "storage/block.h"
#include "storage/itemptr.h"
+/*
+ * Special area of BRIN pages.
+ *
+ * We define it in this odd way so that it always occupies the last
+ * MAXALIGN-sized element of each page.
+ */
+typedef struct BrinSpecialSpace
+{
+ uint16 vector[MAXALIGN(1) / sizeof(uint16)];
+} BrinSpecialSpace;
+
+/*
+ * Make the page type be the last half-word in the page, for consumption by
+ * pg_filedump and similar utilities. We don't really care much about the
+ * position of the "flags" half-word, but it's simpler to apply a consistent
+ * rule to both.
+ *
+ * See comments above GinPageOpaqueData.
+ */
+#define BrinPageType(page) \
+ (((BrinSpecialSpace *) \
+ PageGetSpecialPointer(page))->vector[MAXALIGN(1) / sizeof(uint16) - 1])
+
+#define BrinPageFlags(page) \
+ (((BrinSpecialSpace *) \
+ PageGetSpecialPointer(page))->vector[MAXALIGN(1) / sizeof(uint16) - 2])
+
/* special space on all BRIN pages stores a "type" identifier */
#define BRIN_PAGETYPE_META 0xF091
#define BRIN_PAGETYPE_REVMAP 0xF092
#define BRIN_PAGETYPE_REGULAR 0xF093
-#define BRIN_PAGE_TYPE(page) \
- (((BrinSpecialSpace *) PageGetSpecialPointer(page))->type)
-#define BRIN_IS_REVMAP_PAGE(page) (BRIN_PAGE_TYPE(page) == BRIN_PAGETYPE_REVMAP)
-#define BRIN_IS_REGULAR_PAGE(page) (BRIN_PAGE_TYPE(page) == BRIN_PAGETYPE_REGULAR)
+#define BRIN_IS_REVMAP_PAGE(page) (BrinPageType(page) == BRIN_PAGETYPE_REVMAP)
+#define BRIN_IS_REGULAR_PAGE(page) (BrinPageType(page) == BRIN_PAGETYPE_REGULAR)
/* flags for BrinSpecialSpace */
#define BRIN_EVACUATE_PAGE (1 << 0)
-typedef struct BrinSpecialSpace
-{
- uint16 flags;
- uint16 type;
-} BrinSpecialSpace;
/* Metapage definitions */
typedef struct BrinMetaPageData
diff --git a/src/include/access/gin_private.h b/src/include/access/gin_private.h
index c1a2049..c9f2026 100644
--- a/src/include/access/gin_private.h
+++ b/src/include/access/gin_private.h
@@ -24,10 +24,10 @@
* Note: GIN does not include a page ID word as do the other index types.
* This is OK because the opaque data is only 8 bytes and so can be reliably
* distinguished by size. Revisit this if the size ever increases.
- * Further note: as of 9.2, SP-GiST also uses 8-byte special space. This is
- * still OK, as long as GIN isn't using all of the high-order bits in its
- * flags word, because that way the flags word cannot match the page ID used
- * by SP-GiST.
+ * Further note: as of 9.2, SP-GiST also uses 8-byte special space, as does
+ * BRIN as of 9.5. This is still OK, as long as GIN isn't using all of the
+ * high-order bits in its flags word, because that way the flags word cannot
+ * match the page IDs used by SP-GiST and BRIN.
*/
typedef struct GinPageOpaqueData
{
diff --git a/src/include/access/spgist_private.h b/src/include/access/spgist_private.h
index 0492ef6..413f71e 100644
--- a/src/include/access/spgist_private.h
+++ b/src/include/access/spgist_private.h
@@ -64,6 +64,8 @@ typedef SpGistPageOpaqueData *SpGistPageOpaque;
* which otherwise would have a hard time telling pages of different index
* types apart. It should be the last 2 bytes on the page. This is more or
* less "free" due to alignment considerations.
+ *
+ * See comments above GinPageOpaqueData.
*/
#define SPGIST_PAGE_ID 0xFF82
--
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