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Crash Recovery

I learned from this page.

When is crash recovery used?

  • When you crash and restart
  • After restoring from backups
  • Restarting after fast shutdown

Check for unclean shutdown

  • Redo logs and system tablespace are opened.
  • Checkpoints are read to find highest checkpoint number.
  • Redo logs are scanned starting from latest checkpoint.
  • Crash recovery is initiated if any redo records are found.

Create file-per-table space ID mapping

  • Open all .ibd files in directories within the data directory.
  • Read their space ID from the page 0 (FSP_HDR) header.
  • Populate the space ID to table name mapping.

In Face, if the most recent copy of the page 0 is stored in SSD cache, it should be read in from the SSD cache, instead of the storage.

Torn page recovery

All 128 pages from the doublewrite buffer are examined:

  • Each "target" page from the tablespace is read.
  • If the header and trailer LSN do not match or the page checksum is invalid, the page is restored from the doublewrite buffer.
  • If the doublewrite buffer version of the page is also corrupt, the server will assert(crash).

FaCE does not use doublewrite buffer. So this sequences should be replaced with SSD cache (that is, instead of restoring pages from doublewrite buffer, restores pages from the SSD cache).

Rollback of uncommitted transactions

  • Transaction system (rollback segments) is initialized.
  • Transactions corresponding to "active" undo logs are resurrected.
  • Redo log records are applied since the latest checkpoint.
  • Active transactions are rolled back (using undo logs).