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Back-patch fix for 'Sorcerer's Apprentice' syndrome wherein md.c would

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create a vast quantity of zero-length files if asked to access a block
number far beyond the actual end of a relation.
This commit is contained in:
Tom Lane
2000-09-23 22:11:41 +00:00
parent aa09aaabff
commit 403bdc4ec1
1 changed files with 42 additions and 14 deletions
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56
src/backend/storage/smgr/md.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/smgr/md.c,v 1.68 2000/05/25 23:30:20 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/storage/smgr/md.c,v 1.68.2.1 2000/09/23 22:11:41 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -130,6 +130,7 @@ mdcreate(Relation reln)
char *path;
Assert(reln->rd_unlinked && reln->rd_fd < 0);
path = relpath(RelationGetPhysicalRelationName(reln));
#ifndef __CYGWIN32__
fd = FileNameOpenFile(path, O_RDWR | O_CREAT | O_EXCL, 0600);
@ -138,19 +139,21 @@ mdcreate(Relation reln)
#endif
/*
* For cataloged relations, pg_class is guaranteed to have a unique
* record with the same relname by the unique index. So we are able to
* reuse existent files for new cataloged relations. Currently we reuse
* them in the following cases. 1. they are empty. 2. they are used
* for Index relations and their size == BLCKSZ * 2.
*
* During bootstrap processing, we skip that check, because pg_time,
* pg_variable, and pg_log get created before their .bki file entries
* are processed.
*
* For cataloged relations,pg_class is guaranteed to have an unique
* record with the same relname by the unique index. So we are able to
* reuse existent files for new catloged relations. Currently we reuse
* them in the following cases. 1. they are empty. 2. they are used
* for Index relations and their size == BLCKSZ * 2.
*/
if (fd < 0)
{
int save_errno = errno;
if (!IsBootstrapProcessingMode() &&
reln->rd_rel->relkind == RELKIND_UNCATALOGED)
return -1;
@ -161,11 +164,15 @@ mdcreate(Relation reln)
fd = FileNameOpenFile(path, O_RDWR | O_BINARY, 0600);
#endif
if (fd < 0)
{
/* be sure to return the error reported by create, not open */
errno = save_errno;
return -1;
}
if (!IsBootstrapProcessingMode())
{
bool reuse = false;
int len = FileSeek(fd, 0L, SEEK_END);
long len = FileSeek(fd, 0L, SEEK_END);
if (len == 0)
reuse = true;
@ -175,9 +182,12 @@ mdcreate(Relation reln)
if (!reuse)
{
FileClose(fd);
/* be sure to return the error reported by create */
errno = save_errno;
return -1;
}
}
errno = 0;
}
reln->rd_unlinked = false;
@ -733,9 +743,16 @@ mdnblocks(Relation reln)
if (v->mdfd_chain == (MdfdVec *) NULL)
{
/*
* Because we pass O_CREAT, we will create the next segment
* (with zero length) immediately, if the last segment is of
* length REL_SEGSIZE. This is unnecessary but harmless, and
* testing for the case would take more cycles than it seems
* worth.
*/
v->mdfd_chain = _mdfd_openseg(reln, segno, O_CREAT);
if (v->mdfd_chain == (MdfdVec *) NULL)
elog(ERROR, "cannot count blocks for %s -- open failed",
elog(ERROR, "cannot count blocks for %s -- open failed: %m",
RelationGetRelationName(reln));
}
@ -1075,11 +1092,20 @@ _mdfd_getseg(Relation reln, int blkno)
if (v->mdfd_chain == (MdfdVec *) NULL)
{
v->mdfd_chain = _mdfd_openseg(reln, i, O_CREAT);
/*
* We will create the next segment only if the target block
* is within it. This prevents Sorcerer's Apprentice syndrome
* if a bug at higher levels causes us to be handed a ridiculously
* large blkno --- otherwise we could create many thousands of
* empty segment files before reaching the "target" block. We
* should never need to create more than one new segment per call,
* so this restriction seems reasonable.
*/
v->mdfd_chain = _mdfd_openseg(reln, i, (segno == 1) ? O_CREAT : 0);
if (v->mdfd_chain == (MdfdVec *) NULL)
elog(ERROR, "cannot open segment %d of relation %s",
i, RelationGetRelationName(reln));
elog(ERROR, "cannot open segment %d of relation %s (target block %d): %m",
i, RelationGetRelationName(reln), blkno);
}
v = v->mdfd_chain;
}
@ -1097,8 +1123,10 @@ _mdfd_getseg(Relation reln, int blkno)
* "blind" with no Relation struct. We assume that we are not likely to
* touch the same relation again soon, so we do not create an FD entry for
* the relation --- we just open a kernel file descriptor which will be
* used and promptly closed. The return value is the kernel descriptor,
* or -1 on failure.
* used and promptly closed. We also assume that the target block already
* exists, ie, we need not extend the relation.
*
* The return value is the kernel descriptor, or -1 on failure.
*/
static int