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@ -112,19 +112,25 @@ public: |
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@sa Comments for MDL_object_lock::can_grant_lock() and |
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MDL_scoped_lock::can_grant_lock() for details. |
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Scoped locks are GLOBAL READ LOCK, COMMIT and database (or schema) locks. |
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The object locks are for tables, triggers etc. |
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*/ |
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enum enum_mdl_type { |
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/* |
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An intention exclusive metadata lock. Used only for scoped locks. |
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An intention exclusive metadata lock (IX). Used only for scoped locks. |
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Owner of this type of lock can acquire upgradable exclusive locks on |
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individual objects. |
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Compatible with other IX locks, but is incompatible with scoped S and |
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X locks. |
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IX lock is taken in SCHEMA namespace when we intend to modify |
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object metadata. Object may refer table, stored procedure, trigger, |
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view/etc. |
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*/ |
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MDL_INTENTION_EXCLUSIVE= 0, |
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/* |
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A shared metadata lock. |
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A shared metadata lock (S). |
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To be used in cases when we are interested in object metadata only |
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and there is no intention to access object data (e.g. for stored |
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routines or during preparing prepared statements). |
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@ -144,6 +150,9 @@ enum enum_mdl_type { |
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use SNRW locks for them. It also does not arise when S locks are used |
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during PREPARE calls as table-level locks are not acquired in this |
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case. |
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This lock is taken for global read lock, when caching a stored |
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procedure in memory for the duration of the transaction and for |
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tables used by prepared statements. |
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*/ |
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MDL_SHARED, |
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/* |
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@ -164,8 +173,8 @@ enum enum_mdl_type { |
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*/ |
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MDL_SHARED_HIGH_PRIO, |
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/* |
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A shared metadata lock for cases when there is an intention to read data |
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from table. |
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A shared metadata lock (SR) for cases when there is an intention to read |
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data from table. |
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A connection holding this kind of lock can read table metadata and read |
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table data (after acquiring appropriate table and row-level locks). |
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This means that one can only acquire TL_READ, TL_READ_NO_INSERT, and |
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@ -175,7 +184,7 @@ enum enum_mdl_type { |
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*/ |
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MDL_SHARED_READ, |
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/* |
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A shared metadata lock for cases when there is an intention to modify |
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A shared metadata lock (SW) for cases when there is an intention to modify |
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(and not just read) data in the table. |
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A connection holding SW lock can read table metadata and modify or read |
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table data (after acquiring appropriate table and row-level locks). |
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@ -185,8 +194,8 @@ enum enum_mdl_type { |
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*/ |
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MDL_SHARED_WRITE, |
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/* |
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An upgradable shared metadata lock for cases when there is an intention |
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to modify (and not just read) data in the table. |
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An upgradable shared metadata lock for cases when there is an |
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intention to modify (and not just read) data in the table. |
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Can be upgraded to MDL_SHARED_NO_WRITE and MDL_EXCLUSIVE. |
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A connection holding SU lock can read table metadata and modify or read |
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table data (after acquiring appropriate table and row-level locks). |
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@ -226,7 +235,7 @@ enum enum_mdl_type { |
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*/ |
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MDL_SHARED_NO_READ_WRITE, |
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/* |
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An exclusive metadata lock. |
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An exclusive metadata lock (X). |
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A connection holding this lock can modify both table's metadata and data. |
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No other type of metadata lock can be granted while this lock is held. |
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To be used for CREATE/DROP/RENAME TABLE statements and for execution of |
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@ -234,7 +243,8 @@ enum enum_mdl_type { |
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*/ |
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MDL_EXCLUSIVE, |
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/* This should be the last !!! */ |
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MDL_TYPE_END}; |
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MDL_TYPE_END |
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}; |
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/** Duration of metadata lock. */ |
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Monty
7 years ago