- InnoDB fails to shrink the system tablespace when it contains
the leaked undo log pages caused by MDEV-30671.
- InnoDB does free the unused segment in system tablespace
before shrinking the tablespace. InnoDB fails to free
the unused segment if XA PREPARE transaction exist or
if the previous shutdown was not with innodb_fast_shutdown=0
inode_info: Structure to store the inode page and offsets.
fil_space_t::garbage_collect(): Frees the system tablespace
unused segment
fsp_get_sys_used_segment(): Iterates through all default
file segment and index segment present in system tablespace.
trx_sys_t::is_xa_exist(): Returns true if the XA transaction
exist in the undo logs
fseg_inode_free(): Frees the extents, fragment pages for the
given index node and ignores any error similar to
trx_purge_free_segment()
trx_sys_t::reset_page(): Retain the TRX_SYS_FSEG_HEADER value
in trx_sys page while resetting the page.
- Introduce the option :autoshrink attribute to be
added to innodb_data_file_path variable to allow
the shrinking of system tablespace during startup process.
Steps for shrinking the system tablespace:
1) Find the last used extent in system tablespace
by iterating through the BITMAP in extent descriptor pages
2) If the last used extent is lesser than user specified size
then set desired target size to user specified size.
3) Store the page contents of "to be modified" extent
descriptor pages, latches the "to be modified"
extent descriptor pages and check for buffer pool
memory availability
4) Make checkpoint to flush all pages in buffer pool, so
that pages in flush list doesn't have to use doublewrite
buffer and disable doublewrite buffer during shrinking process
5) Update the FSP_SIZE and FSP_FREE_LIMIT in header page
6) Remove the "to be truncated" pages from FSP_FREE and
FSP_FREE_FRAG list
7) Reset the bitmap in the last descriptor pages for the
"to be truncated" pages.
8) In case of multiple files, calculate the truncated last
file size and do the truncation in last file
9) Check whether mini-transaction log size doesn't exceed
the minimum value of innodb_log_buffer_size which is 2MB.
In that case, replace the modified buffer pool pages with
the page old content.
11) Commit the mini-transaction for shrinking the tablespace
and enable/disable the doublewrite buffer depends on user
specified value.
recv_sys_t::apply(): Handle the truncation of system tablespace
only if the recovered tablespace size is lesser than actual
existing size.
