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Fix locking while setting flags in MySerializableXact.

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Even if a flag is modified only by the backend owning the transaction, it's
not safe to modify it without a lock. Another backend might be setting or
clearing a different flag in the flags field concurrently, and that
operation might be lost because setting or clearing a bit in a word is not
atomic.

Make did-write flag a simple backend-private boolean variable, because it
was only set or tested in the owning backend (except when committing a
prepared transaction, but it's not worthwhile to optimize for the case of a
read-only prepared transaction). This also eliminates the need to add
locking where that flag is set.

Also, set the did-write flag when doing DDL operations like DROP TABLE or
TRUNCATE -- that was missed earlier.
This commit is contained in:
Heikki Linnakangas
2011-06-10 23:15:05 +03:00
parent d69149ed71
commit cb2d158c58
2 changed files with 61 additions and 39 deletions
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15
src/include/storage/predicate_internals.h
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@@ -99,14 +99,13 @@ typedef struct SERIALIZABLEXACT
*/
#define SXACT_FLAG_CONFLICT_OUT 0x00000004
#define SXACT_FLAG_READ_ONLY 0x00000008
#define SXACT_FLAG_DID_WRITE 0x00000010
#define SXACT_FLAG_MARKED_FOR_DEATH 0x00000020
#define SXACT_FLAG_DEFERRABLE_WAITING 0x00000040
#define SXACT_FLAG_RO_SAFE 0x00000080
#define SXACT_FLAG_RO_UNSAFE 0x00000100
#define SXACT_FLAG_SUMMARY_CONFLICT_IN 0x00000200
#define SXACT_FLAG_SUMMARY_CONFLICT_OUT 0x00000400
#define SXACT_FLAG_PREPARED 0x00000800
#define SXACT_FLAG_MARKED_FOR_DEATH 0x00000010
#define SXACT_FLAG_DEFERRABLE_WAITING 0x00000020
#define SXACT_FLAG_RO_SAFE 0x00000040
#define SXACT_FLAG_RO_UNSAFE 0x00000080
#define SXACT_FLAG_SUMMARY_CONFLICT_IN 0x00000100
#define SXACT_FLAG_SUMMARY_CONFLICT_OUT 0x00000200
#define SXACT_FLAG_PREPARED 0x00000400
/*
* The following types are used to provide an ad hoc list for holding