#include <trx0trx.h>
Detailed Description
The transaction handle
Normally, there is a 1:1 relationship between a transaction handle (trx) and a session (client connection). One session is associated with exactly one user transaction. There are some exceptions to this:
For DDL operations, a subtransaction is allocated that modifies the data dictionary tables. Lock waits and deadlocks are prevented by acquiring the dict_operation_lock before starting the subtransaction and releasing it after committing the subtransaction.
The purge system uses a special transaction that is not associated with any session.
If the system crashed or it was quickly shut down while there were transactions in the ACTIVE or PREPARED state, these transactions would no longer be associated with a session when the server is restarted.
A session may be served by at most one thread at a time. The serving thread of a session might change in some MySQL implementations. Therefore we do not have os_thread_get_curr_id() assertions in the code.
Normally, only the thread that is currently associated with a running transaction may access (read and modify) the trx object, and it may do so without holding any mutex. The following are exceptions to this:
trx_rollback_resurrected() may access resurrected (connectionless) transactions while the system is already processing new user transactions. The trx_sys->mutex prevents a race condition between it and lock_trx_release_locks() [invoked by trx_commit()].
trx_print_low() may access transactions not associated with the current thread. The caller must be holding trx_sys->mutex and lock_sys->mutex.
When a transaction handle is in the trx_sys->mysql_trx_list or trx_sys->trx_list, some of its fields must not be modified without holding trx_sys->mutex exclusively.
The locking code (in particular, lock_deadlock_recursive() and lock_rec_convert_impl_to_expl()) will access transactions associated to other connections. The locks of transactions are protected by lock_sys->mutex and sometimes by trx->mutex.
Field Documentation
| bool trx_t::api_auto_commit |
automatic commit
| bool trx_t::api_trx |
trx started by InnoDB API
| ibool trx_t::auto_commit |
TRUE if it is an autocommit
| ulint trx_t::check_foreigns |
normally TRUE, but if the user wants to suppress foreign key checks, (in table imports, for example) we set this FALSE
| ulint trx_t::check_unique_secondary |
normally TRUE, but if the user wants to speed up inserts by suppressing unique key checks for secondary indexes when we decide if we can use the insert buffer for them, we set this FALSE
| lsn_t trx_t::commit_lsn |
lsn at the time of the commit
| bool trx_t::ddl |
true if it is a transaction that is being started for a DDL operation
| ulint trx_t::declared_to_be_inside_innodb |
this is TRUE if we have declared this transaction in srv_conc_enter_innodb to be inside the InnoDB engine
| char trx_t::detailed_error[256] |
detailed error message for last error, or empty.
| trx_dict_op_t trx_t::dict_operation |
- See Also
- enum trx_dict_op
| ulint trx_t::dict_operation_lock_mode |
0, RW_S_LATCH, or RW_X_LATCH: the latch mode trx currently holds on dict_operation_lock. Protected by dict_operation_lock.
| ulint trx_t::duplicates |
TRX_DUP_IGNORE | TRX_DUP_REPLACE
| const dict_index_t* trx_t::error_info |
if the error number indicates a duplicate key error, a pointer to the problematic index is stored here
| ulint trx_t::error_key_num |
if the index creation fails to a duplicate key error, a mysql key number of that index is stored here
| dberr_t trx_t::error_state |
0 if no error, otherwise error number; NOTE That ONLY the thread doing the transaction is allowed to set this field: this is NOT protected by any mutex
| ulint trx_t::flush_tables |
if "covering" the FLUSH TABLES", count of tables being flushed.
| fts_trx_t* trx_t::fts_trx |
FTS information, or NULL if transaction hasn't modified tables with FTS indexes (yet).
| read_view_t* trx_t::global_read_view |
consistent read view associated to a transaction or NULL
| mem_heap_t* trx_t::global_read_view_heap |
memory heap for the global read view
| que_t* trx_t::graph |
query currently run in the session, or NULL if none; NOTE that the query belongs to the session, and it can survive over a transaction commit, if it is a stored procedure with a COMMIT WORK statement, for instance
| ulint trx_t::has_search_latch |
TRUE if this trx has latched the search system latch in S-mode
| trx_id_t trx_t::id |
transaction id
| ibool trx_t::in_mysql_trx_list |
TRUE if in trx_sys->mysql_trx_list
| ibool trx_t::in_ro_trx_list |
The following two fields are mutually exclusive. TRUE if in trx_sys->ro_trx_list
| ibool trx_t::in_rw_trx_list |
TRUE if in trx_sys->rw_trx_list
| trx_undo_t* trx_t::insert_undo |
pointer to the insert undo log, or NULL if no inserts performed yet
| ulint trx_t::is_recovered |
0=normal transaction, 1=recovered, must be rolled back, protected by trx_sys->mutex when trx->in_rw_trx_list holds
| ulint trx_t::isolation_level |
TRX_ISO_REPEATABLE_READ, ...
| trx_savept_t trx_t::last_sql_stat_start |
undo_no when the last sql statement was started: in case of an error, trx is rolled back down to this undo number; see note at undo_mutex!
| trx_lock_t trx_t::lock |
Information about the transaction locks and state. Protected by trx->mutex or lock_sys->mutex or both
| ulint trx_t::must_flush_log_later |
this flag is set to TRUE in trx_commit() if flush_log_later was TRUE, and there were modifications by the transaction; in that case we must flush the log in trx_commit_complete_for_mysql()
| ib_mutex_t trx_t::mutex |
Mutex protecting the fields state and lock (except some fields of lock, which are protected by lock_sys->mutex)
| const char* trx_t::mysql_log_file_name |
if MySQL binlog is used, this field contains a pointer to the latest file name; this is NULL if binlog is not used
| ib_int64_t trx_t::mysql_log_offset |
if MySQL binlog is used, this field contains the end offset of the binlog entry
| ulint trx_t::mysql_n_tables_locked |
how many tables the current SQL statement uses, except those in consistent read
| THD* trx_t::mysql_thd |
MySQL thread handle corresponding to this trx, or NULL
| ut_list_node< trx_t > trx_t::mysql_trx_list |
list of transactions created for MySQL; protected by trx_sys->mutex
| ulint trx_t::n_autoinc_rows |
no. of AUTO-INC rows required for an SQL statement. This is useful for multi-row INSERTs
| ulint trx_t::n_mysql_tables_in_use |
number of Innobase tables used in the processing of the current SQL statement in MySQL
| ulint trx_t::n_tickets_to_enter_innodb |
this can be > 0 only when declared_to_... is TRUE; when we come to srv_conc_innodb_enter, if the value here is > 0, we decrement this by 1
| trx_id_t trx_t::no |
transaction serialization number: max trx id shortly before the transaction is moved to COMMITTED_IN_MEMORY state. Protected by trx_sys_t::mutex when trx->in_rw_trx_list. Initially set to TRX_ID_MAX.
| const char* trx_t::op_info |
English text describing the current operation, or an empty string
| ulint trx_t::pages_undone |
number of undo log pages undone since the last undo log truncation
| ibool trx_t::read_only |
TRUE if transaction is flagged as a READ-ONLY transaction. if !auto_commit || will_lock > 0 then it will added to the list trx_sys_t::ro_trx_list. A read only transaction will not be assigned an UNDO log. Non-locking auto-commit read-only transaction will not be on either list.
| read_view_t* trx_t::read_view |
consistent read view used in the transaction or NULL, this read view if defined can be normal read view associated to a transaction (i.e. same as global_read_view) or read view associated to a cursor
| bool trx_t::read_write |
if read and write operation
| undo_no_t trx_t::roll_limit |
least undo number to undo during a rollback
| trx_rseg_t* trx_t::rseg |
rollback segment assigned to the transaction, or NULL if not assigned yet
| ulint trx_t::search_latch_timeout |
If we notice that someone is waiting for our S-lock on the search latch to be released, we wait in row0sel.cc for BTR_SEA_TIMEOUT new searches until we try to keep the search latch again over calls from MySQL; this is intended to reduce contention on the search latch
| sess_t* trx_t::sess |
session of the trx, NULL if none
| const char* trx_t::start_file |
Filename where it was started
| ulint trx_t::start_line |
Track where it was started from
| time_t trx_t::start_time |
time the trx state last time became TRX_STATE_ACTIVE
| trx_state_t trx_t::state |
State of the trx from the point of view of concurrency control
and the valid state transitions.
Possible states:
TRX_STATE_NOT_STARTED TRX_STATE_ACTIVE TRX_STATE_PREPARED TRX_STATE_COMMITTED_IN_MEMORY (alias below COMMITTED)
Valid state transitions are:
Regular transactions: NOT_STARTED -> ACTIVE -> COMMITTED -> NOT_STARTED
Auto-commit non-locking read-only: NOT_STARTED -> ACTIVE -> NOT_STARTED
XA (2PC): NOT_STARTED -> ACTIVE -> PREPARED -> COMMITTED -> NOT_STARTED
Recovered XA: NOT_STARTED -> PREPARED -> COMMITTED -> (freed)
XA (2PC) (shutdown before ROLLBACK or COMMIT): NOT_STARTED -> PREPARED -> (freed)
Latching and various transaction lists membership rules:
XA (2PC) transactions are always treated as non-autocommit.
Transitions to ACTIVE or NOT_STARTED occur when !in_rw_trx_list and !in_ro_trx_list (no trx_sys->mutex needed).
Autocommit non-locking read-only transactions move between states without holding any mutex. They are !in_rw_trx_list, !in_ro_trx_list.
When a transaction is NOT_STARTED, it can be in_mysql_trx_list if it is a user transaction. It cannot be in ro_trx_list or rw_trx_list.
ACTIVE->PREPARED->COMMITTED is only possible when trx->in_rw_trx_list. The transition ACTIVE->PREPARED is protected by trx_sys->mutex.
ACTIVE->COMMITTED is possible when the transaction is in ro_trx_list or rw_trx_list.
Transitions to COMMITTED are protected by both lock_sys->mutex and trx->mutex.
NOTE: Some of these state change constraints are an overkill, currently only required for a consistent view for printing stats. This unnecessarily adds a huge cost for the general case.
NOTE: In the future we should add read only transactions to the ro_trx_list the first time they try to acquire a lock ie. by default we treat all read-only transactions as non-locking.
| ulint trx_t::support_xa |
normally we do the XA two-phase commit steps, but by setting this to FALSE, one can save CPU time and about 150 bytes in the undo log size as then we skip XA steps
| table_id_t trx_t::table_id |
Table to drop iff dict_operation == TRX_DICT_OP_TABLE, or 0.
| ut_list_node< trx_t > trx_t::trx_list |
list of transactions; protected by trx_sys->mutex. The same node is used for both trx_sys_t::ro_trx_list and trx_sys_t::rw_trx_list
| ut_list_base< trx_named_savept_t > trx_t::trx_savepoints |
savepoints set with SAVEPOINT ..., oldest first
| ib_mutex_t trx_t::undo_mutex |
mutex protecting the fields in this section (down to undo_no_arr), EXCEPT last_sql_stat_start, which can be accessed only when we know that there cannot be any activity in the undo logs!
| undo_no_t trx_t::undo_no |
next undo log record number to assign; since the undo log is private for a transaction, this is a simple ascending sequence with no gaps; thus it represents the number of modified/inserted rows in a transaction
| trx_undo_arr_t* trx_t::undo_no_arr |
array of undo numbers of undo log records which are currently processed by a rollback operation
| trx_undo_t* trx_t::update_undo |
pointer to the update undo log, or NULL if no update performed yet
| ulint trx_t::will_lock |
Will acquire some locks. Increment each time we determine that a lock will be acquired by the MySQL layer.
| XID trx_t::xid |
X/Open XA transaction identification to identify a transaction branch
The documentation for this struct was generated from the following file:
- include/trx0trx.h
