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Commit63735ca

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Dept. of second thoughts: add comments cautioning against using
ReadOrZeroBuffer to fetch pages from beyond physical EOF. This wouldusually work, but would cause problems for md.c if writes occurredbeyond a segment boundary when the previous segment file hadn't beenfully extended.
1 parent8c3cc86 commit63735ca

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‎src/backend/storage/buffer/bufmgr.c

Lines changed: 7 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.217 2007/05/02 23:18:03 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.218 2007/05/02 23:34:48 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -21,7 +21,9 @@
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*cache we don't read it, but just return a zeroed-out buffer. Useful
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*when the caller intends to fill the page from scratch, since this
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*saves I/O and avoids unnecessary failure if the page-on-disk has
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*corrupt page headers.
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*corrupt page headers. Caution: do not use this to read a page that
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*is beyond the relation's current physical EOF; that is likely to
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*cause problems in md.c when the page is modified and written out.
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*
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* ReleaseBuffer() -- unpin a buffer
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*
@@ -137,6 +139,9 @@ ReadBuffer(Relation reln, BlockNumber blockNum)
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*cache already, it's filled with zeros instead of reading it from
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*disk. The caller is expected to overwrite the whole buffer,
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*so that the current page contents are not interesting.
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*Caution: do not use this to read a page that is beyond the relation's
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*current physical EOF; that is likely to cause problems in md.c when
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*the page is modified and written out. P_NEW is OK, though.
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*/
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Buffer
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ReadOrZeroBuffer(Relationreln,BlockNumberblockNum)

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