Bug: fseg_get_pages_info does not release pages during extent iteration

Bug: fseg_get_pages_info does not release pages during extent iteration

Problem

In fseg_get_pages_info() (storage/innobase/fsp/fsp0fsp.cc), when scanning the FSEG_NOT_FULL and FSEG_FULL extent lists for a segment, the mtr holds latches on every visited page descriptor (xdes) without releasing them until the entire function completes and mtr_commit() is called.

For tables with a large number of extents (large tables or tables with fragmented segments), this can mean holding hundreds or thousands of page latches simultaneously within a single mini-transaction. This causes:

• Excessive buffer pool frame consumption (each latched page pins a buffer pool frame)
• Increased memory pressure and potential OOM
• CHECK INDEX on large tables becomes unreliable (may OOM)

Root Cause

The mtr_t memo stack grows unbounded during extent list traversal in fseg_get_pages_info(). Each call to xdes_lst_get_descriptor() and xdes_mtr_get_bit() adds a page latch to the mtr memo, but these latches are only released at mtr_commit() which happens at the very end of the function.

Fix

Add a new function mtr_t::release_all_after_savepoint() that releases all pages held in the mtr memo after a given savepoint. Then in fseg_get_pages_info(), set a savepoint and release pages every 100 iterations, effectively bounding the number of simultaneously held latches.

Changes

1. storage/innobase/include/mtr0mtr.h: Declare release_all_after_savepoint(ulint savepoint) method and mtr_release_all_after_savepoint() macro.

2. storage/innobase/mtr/mtr0mtr.cc: Implement Release_all_after_savepoint functor and mtr_t::release_all_after_savepoint() method.

3. storage/innobase/fsp/fsp0fsp.cc: In fseg_get_pages_info(), add savepoint and release logic every 100 pages during FSEG_NOT_FULL and FSEG_FULL list scans.

Affected Scenarios

• CHECK INDEX on large tables — ha_innobase::check_index() → innobase_get_index_status() → fseg_get_pages_info() for both leaf and top segments of each index

Empieza leyendo fseg_get_pages_info() en storage/innobase/fsp/fsp0fsp.cc y, después, inspecciona las declaraciones y la implementación de mtr_t en storage/innobase/include/mtr0mtr.h y storage/innobase/mtr/mtr0mtr.cc. Sigue la ruta de CHECK INDEX descrita en el issue. Se considera terminado cuando los escaneos de extents limitan los page latches retenidos, preservando los resultados existentes de información de páginas y el comportamiento de CHECK INDEX.