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This should be functionally equivalent to WL#6204 in MySQL 8.0.0, with the notable difference that the file format changes are limited to repurposing a previously unused data field in B-tree pages. For persistent InnoDB tables, write the last used AUTO_INCREMENT value to the root page of the clustered index, in the previously unused (0) PAGE_MAX_TRX_ID field, now aliased as PAGE_ROOT_AUTO_INC. Unlike some other previously unused InnoDB data fields, this one was actually always zero-initialized, at least since MySQL 3.23.49. The writes to PAGE_ROOT_AUTO_INC are protected by SX or X latch on the root page. The SX latch will allow concurrent read access to the root page. (The field PAGE_ROOT_AUTO_INC will only be read on the first-time call to ha_innobase::open() from the SQL layer. The PAGE_ROOT_AUTO_INC can only be updated when executing SQL, so read/write races are not possible.) During INSERT, the PAGE_ROOT_AUTO_INC is updated by the low-level function btr_cur_search_to_nth_level(), adding no extra page access. [Adaptive hash index lookup will be disabled during INSERT.] If some rare UPDATE modifies an AUTO_INCREMENT column, the PAGE_ROOT_AUTO_INC will be adjusted in a separate mini-transaction in ha_innobase::update_row(). When a page is reorganized, we have to preserve the PAGE_ROOT_AUTO_INC field. During ALTER TABLE, the initial AUTO_INCREMENT value will be copied from the table. ALGORITHM=COPY and online log apply in LOCK=NONE will update PAGE_ROOT_AUTO_INC in real time. innodb_col_no(): Determine the dict_table_t::cols[] element index corresponding to a Field of a non-virtual column. (The MySQL 5.7 implementation of virtual columns breaks the 1:1 relationship between Field::field_index and dict_table_t::cols[]. Virtual columns are omitted from dict_table_t::cols[]. Therefore, we must translate the field_index of AUTO_INCREMENT columns into an index of dict_table_t::cols[].) Upgrade from old data files: By default, the AUTO_INCREMENT sequence in old data files would appear to be reset, because PAGE_MAX_TRX_ID or PAGE_ROOT_AUTO_INC would contain the value 0 in each clustered index page. In new data files, PAGE_ROOT_AUTO_INC can only be 0 if the table is empty or does not contain any AUTO_INCREMENT column. For backward compatibility, we use the old method of SELECT MAX(auto_increment_column) for initializing the sequence. btr_read_autoinc(): Read the AUTO_INCREMENT sequence from a new-format data file. btr_read_autoinc_with_fallback(): A variant of btr_read_autoinc() that will resort to reading MAX(auto_increment_column) for data files that did not use AUTO_INCREMENT yet. It was manually tested that during the execution of innodb.autoinc_persist the compatibility logic is not activated (for new files, PAGE_ROOT_AUTO_INC is never 0 in nonempty clustered index root pages). initialize_auto_increment(): Replaces ha_innobase::innobase_initialize_autoinc(). This initializes the AUTO_INCREMENT metadata. Only called from ha_innobase::open(). ha_innobase::info_low(): Do not try to lazily initialize dict_table_t::autoinc. It must already have been initialized by ha_innobase::open() or ha_innobase::create(). Note: The adjustments to class ha_innopart were not tested, because the source code (native InnoDB partitioning) is not being compiled. |
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