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- With the help of MDEV-14795, InnoDB implemented a way to shrink the InnoDB system tablespace after undo tablespaces have been moved to separate files (MDEV-29986). There is no way to defragment any pages of InnoDB system tables. By doing that, shrinking of system tablespace can be more effective. This patch deals with defragment of system tables inside ibdata1. Following steps are done to do the defragmentation of system tablespace: 1) Make sure that there is no user tables exist in ibdata1 2) Iterate through all extent descriptor pages in system tablespace and note their states. 3) Find the free earlier extent to replace the lastly used extents in the system tablespace. 4) Iterate through all indexes of system tablespace and defragment the tree level by level. 5) Iterate the level from left page to right page and find out the page comes under the extent to be replaced. If it is then do step (6) else step(4) 6) Prepare the allocation of new extent by latching necessary pages. If any error happens then there is no modification of page happened till step (5). 7) Allocate the new page from the new extent 8) Prepare the associated pages for the block to be modified 9) Prepare the step of freeing of page 10) If any error happens during preparing of associated pages, freeing of page then restore the page which was modified during new page allocation 11) Copy the old page content to new page 12) Change the associative pages like left, right and parent page 13) Complete the freeing of old page Allocation of page from new extent, changing of relative pages, freeing of page are done by 2 steps. one is prepare which latches the to be modified pages and checks their validation. Other is complete(), Do the operation fseg_validate(): Validate the list exist in inode segment Defragmentation is enabled only when :autoextend exist in innodb_data_file_path variable. |
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