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| author | Keith Bostic <keith@wiredtiger.com> | 2012-08-09 09:33:23 +0000 |
|---|---|---|
| committer | Keith Bostic <keith@wiredtiger.com> | 2012-08-09 09:33:23 +0000 |
| commit | a6185492f9f59512b9a96773d25bbe534701651f (patch) | |
| tree | 7af4409fbd5964a1ed7c438e5d227f41b39dae87 /src/docs/transactions.dox | |
| parent | 18d0434b0109809f139b89d8081ba81736e7a072 (diff) | |
| download | mongo-a6185492f9f59512b9a96773d25bbe534701651f.tar.gz | |
re-work transaction page to list the isolation levels in order of
data/operation protection.
Diffstat (limited to 'src/docs/transactions.dox')
| -rw-r--r-- | src/docs/transactions.dox | 29 |
1 files changed, 15 insertions, 14 deletions
diff --git a/src/docs/transactions.dox b/src/docs/transactions.dox index 60b8a9e4d11..29efd194d88 100644 --- a/src/docs/transactions.dox +++ b/src/docs/transactions.dox @@ -54,30 +54,31 @@ attempts to rollback and update the same value. @section transaction_isolation Isolation levels -WiredTiger supports <code>snapshot</code>, <code>read-committed</code> -and <code>read-uncommitted</code> isolation levels; the default -isolation level is is <code>read-committed</code>. - -- <code>read-committed</code>: -Transactions cannot see changes made by other transactions before those -transactions are committed. Dirty reads are not possible; non-repeatable -reads and phantoms are possible. Read-committed isolation is the -default. +WiredTiger supports <code>read-uncommitted</code>, +<code>read-committed</code> and <code>snapshot</code> isolation levels; +the default isolation level is is <code>read-committed</code>. - <code>read-uncommitted</code>: Transactions can see changes made by other transactions before those transactions are committed. Dirty reads, non-repeatable reads and phantoms are possible. +- <code>read-committed</code>: +Transactions cannot see changes made by other transactions before those +transactions are committed. Dirty reads are not possible; +non-repeatable reads and phantoms are possible. + - <code>snapshot</code>: Transactions read the versions of records committed before the transaction started. Dirty reads and non-repeatable reads are not possible; phantoms -are possible. Snapshot isolation is a strong guarantee, but not equivalent -to a single-threaded execution of the transactions, known as serializable +are possible.<br><br> +Snapshot isolation is a strong guarantee, but not equivalent to a +single-threaded execution of the transactions, known as serializable isolation. Concurrent transactions T1 and T2 running under snapshot -isolation may both commit and produce a state that neither (T1 followed by -T2) or (T2 followed by T1) could have produced, if there is overlap between -T1's reads and T2's writes, and between T1's writes and T2's reads. +isolation may both commit and produce a state that neither (T1 followed +by T2) or (T2 followed by T1) could have produced, if there is overlap +between T1's reads and T2's writes, and between T1's writes and T2's +reads. The transaction isolation level can be configured on a per-transaction basis: |