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The purpose of the change buffer was to reduce random disk access, which could be useful on rotational storage, but maybe less so on solid-state storage. When we wished to (1) insert a record into a non-unique secondary index, (2) delete-mark a secondary index record, (3) delete a secondary index record as part of purge (but not ROLLBACK), and the B-tree leaf page where the record belongs to is not in the buffer pool, we inserted a record into the change buffer B-tree, indexed by the page identifier. When the page was eventually read into the buffer pool, we looked up the change buffer B-tree for any modifications to the page, applied these upon the completion of the read operation. This was called the insert buffer merge. We remove the change buffer, because it has been the source of various hard-to-reproduce corruption bugs, including those fixed in commit5b9ee8d819and commit165564d3c3but not limited to them. A downgrade will fail with a clear message starting with commitdb14eb16f9(MDEV-30106). buf_page_t::state: Merge IBUF_EXIST to UNFIXED and WRITE_FIX_IBUF to WRITE_FIX. buf_pool_t::watch[]: Remove. trx_t: Move isolation_level, check_foreigns, check_unique_secondary, bulk_insert into the same bit-field. The only purpose of trx_t::check_unique_secondary is to enable bulk insert into an empty table. It no longer enables insert buffering for UNIQUE INDEX. btr_cur_t::thr: Remove. This field was originally needed for change buffering. Later, its use was extended to cover SPATIAL INDEX. Much of the time, rtr_info::thr holds this field. When it does not, we will add parameters to SPATIAL INDEX specific functions. ibuf_upgrade_needed(): Check if the change buffer needs to be updated. ibuf_upgrade(): Merge and upgrade the change buffer after all redo log has been applied. Free any pages consumed by the change buffer, and zero out the change buffer root page to mark the upgrade completed, and to prevent a downgrade to an earlier version. dict_load_tablespaces(): Renamed from dict_check_tablespaces_and_store_max_id(). This needs to be invoked before ibuf_upgrade(). btr_cur_open_at_rnd_pos(): Specialize for use in persistent statistics. The change buffer merge does not need this function anymore. btr_page_alloc(): Renamed from btr_page_alloc_low(). We no longer allocate any change buffer pages. btr_cur_open_at_rnd_pos(): Specialize for use in persistent statistics. The change buffer merge does not need this function anymore. row_search_index_entry(), btr_lift_page_up(): Add a parameter thr for the SPATIAL INDEX case. rtr_page_split_and_insert(): Specialized from btr_page_split_and_insert(). rtr_root_raise_and_insert(): Specialized from btr_root_raise_and_insert(). Note: The support for upgrading from the MySQL 3.23 or MySQL 4.0 change buffer format that predates the MySQL 4.1 introduction of the option innodb_file_per_table was removed in MySQL 5.6.5 as part of mysql/mysql-server@69b6241a79 and MariaDB 10.0.11 as part of1d0f70c2f8. In the tests innodb.log_upgrade and innodb.log_corruption, we create valid (upgraded) change buffer pages. Tested by: Matthias Leich
55 lines
2.6 KiB
C
55 lines
2.6 KiB
C
/*****************************************************************************
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Copyright (c) 2023, MariaDB Corporation.
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This program is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free Software
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Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along with
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this program; if not, write to the Free Software Foundation, Inc.,
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA
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*****************************************************************************/
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#include "db0err.h"
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/* The purpose of the change buffer was to reduce random disk access.
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When we wished to
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(1) insert a record into a non-unique secondary index,
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(2) delete-mark a secondary index record,
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(3) delete a secondary index record as part of purge (but not ROLLBACK),
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and the B-tree leaf page where the record belongs to is not in the buffer
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pool, we inserted a record into the change buffer B-tree, indexed by
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the page identifier. When the page was eventually read into the buffer
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pool, we looked up the change buffer B-tree for any modifications to the
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page, applied these upon the completion of the read operation. This
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was called the insert buffer merge.
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There was a hash index of the change buffer B-tree, implemented as the
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"change buffer bitmap". Bits in these bitmap pages indicated how full
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the page roughly was, and whether any records for the page identifier
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exist in the change buffer. The "free" bits had to be updated as part of
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operations that modified secondary index leaf pages.
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Because the change buffer has been removed, we will no longer update
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any change buffer bitmap pages. Instead, on database startup, we will
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check if an upgrade needs to be performed, and apply any buffered
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changes if that is the case. Finally, the change buffer will be
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transformed to a format that will not be recognized by earlier
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versions of MariaDB Server, to prevent downgrades from causing
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corruption (due to the removed updates of the bitmap pages) when the
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change buffer might be enabled. */
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/** Check if ibuf_upgrade() is needed as part of server startup.
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@return error code
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@retval DB_SUCCESS if no upgrade is needed
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@retval DB_FAIL if the change buffer is not empty (need ibuf_upgrade()) */
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dberr_t ibuf_upgrade_needed();
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/** Upgrade the change buffer after all redo log has been applied. */
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dberr_t ibuf_upgrade();
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