diff options
Diffstat (limited to 'sql/handler.h')
| -rw-r--r-- | sql/handler.h | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/sql/handler.h b/sql/handler.h index a5c4af533be..82926dc08c0 100644 --- a/sql/handler.h +++ b/sql/handler.h @@ -667,6 +667,11 @@ struct handlerton full transaction is committed, not for each commit of statement transaction in a multi-statement transaction. + Not that like prepare(), commit_ordered() is only called when 2-phase + commit takes place. Ie. when no binary log and only a single engine + participates in a transaction, one commit() is called, no + commit_orderd(). So engines must be prepared for this. + The calls to commit_ordered() in multiple parallel transactions is guaranteed to happen in the same order in every participating handler. This can be used to ensure the same commit order among multiple @@ -684,11 +689,9 @@ struct handlerton doing any time-consuming or blocking operations in commit_ordered() will limit scalability. - Handlers can rely on commit_ordered() calls for transactions that updated - data to be serialised (no two calls can run in parallel, so no extra - locking on the handler part is required to ensure this). However, calls - for SELECT-only transactions are not serialised, so can occur in parallel - with each other and with at most one write-transaction. + Handlers can rely on commit_ordered() calls to be serialised (no two + calls can run in parallel, so no extra locking on the handler part is + required to ensure this). Note that commit_ordered() can be called from a different thread than the one handling the transaction! So it can not do anything that depends on @@ -700,7 +703,8 @@ struct handlerton must be saved and returned from the commit() method instead. The commit_ordered method is optional, and can be left unset if not - needed in a particular handler. + needed in a particular handler (then there will be no ordering guarantees + wrt. other engines and binary log). */ void (*commit_ordered)(handlerton *hton, THD *thd, bool all); int (*rollback)(handlerton *hton, THD *thd, bool all); |