what is a commit log?

Question

in google's bigtable context, what does a commit log mean? and what is the use of a commit log?

Answer 1

In any database context, a "commit" is the application of a single transaction to the DB. A commit log is a record of transactions. It's used to keep track of what's happening, and help with e.g. disaster recovery - generally, all commits are written to the log before being applied, so transactions that were in flight when the server went down can be recovered and re-applied by checking the log.