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| author | Michael Cahill <michael.cahill@wiredtiger.com> | 2014-09-11 10:30:52 +1000 |
|---|---|---|
| committer | Michael Cahill <michael.cahill@wiredtiger.com> | 2014-09-11 10:30:52 +1000 |
| commit | e535a5202a60050f84cc2a0f8f5cc8c7392b9b20 (patch) | |
| tree | 8106d15947d0b604efcf34f84dc1401540fdc7c9 /src/include/txn.i | |
| parent | cfab614cbb4d2c9f3443a0289eb47476344fb5a3 (diff) | |
| download | mongo-e535a5202a60050f84cc2a0f8f5cc8c7392b9b20.tar.gz | |
Change transaction ID allocation so that if transactions stop, the last ID becomes globally visible. We want post-increment semantics but our atomic primitive is pre-increment.
refs #1200
Diffstat (limited to 'src/include/txn.i')
| -rw-r--r-- | src/include/txn.i | 21 |
1 files changed, 9 insertions, 12 deletions
diff --git a/src/include/txn.i b/src/include/txn.i index 3854429f8e4..81559bfe490 100644 --- a/src/include/txn.i +++ b/src/include/txn.i @@ -179,7 +179,7 @@ __wt_txn_read(WT_SESSION_IMPL *session, WT_UPDATE *upd) /* * __wt_txn_autocommit_check -- - * If an auto-commit transaction is required, start one. + * If an auto-commit transaction is required, start one. */ static inline int __wt_txn_autocommit_check(WT_SESSION_IMPL *session) @@ -195,23 +195,20 @@ __wt_txn_autocommit_check(WT_SESSION_IMPL *session) } /* - * __wt_txn_current_id -- - * Get the current transaction ID. - */ -static inline uint64_t -__wt_txn_current_id(WT_SESSION_IMPL *session) -{ - return (S2C(session)->txn_global.current); -} - -/* * __wt_txn_new_id -- * Allocate a new transaction ID. */ static inline uint64_t __wt_txn_new_id(WT_SESSION_IMPL *session) { - return WT_ATOMIC_ADD(S2C(session)->txn_global.current, 1); + /* + * We want the global value to lead the allocated values, so that any + * allocated transaction ID eventually becomes globally visible. When + * there are no transactions running, the oldest_id will reach the + * global current ID, so we want post-increment semantics. Our atomic + * add primitive does pre-increment, so adjust the result here. + */ + return WT_ATOMIC_ADD(S2C(session)->txn_global.current, 1) - 1; } /* |