An internal buffer being reused immediately after it had been freed could lead to an unplanned data node shutdown. (Bug #27622643)

References: See also: Bug #28698831.

An NDB online backup consists of data, which is fuzzy, and a redo and undo log. To restore to a consistent state it is necessary to ensure that the log contains all of the changes spanning the capture of the fuzzy data portion and beyond to a consistent snapshot point. This is achieved by waiting for a GCI boundary to be passed after the capture of data is complete, but before stopping change logging and recording the stop GCI in the backup's metadata.

At restore time, the log is replayed up to the stop GCI, restoring the system to the state it had at the consistent stop GCI. A problem arose when, under load, it was possible to select a GCI boundary which occurred too early and did not span all the data captured. This could lead to inconsistencies when restoring the backup; these could be be noticed as broken constraints or corrupted BLOB entries.

Now the stop GCI is chosen is so that it spans the entire duration of the fuzzy data capture process, so that the backup log always contains all data within a given stop GCI. (Bug #27497461)

References: See also: Bug #27566346.