Two straightforward changes in Bigtable or Spanner are changing tablet compression settings or tuning compaction more aggressively. Edit: given the mention of

Two straightforward changes in Bigtable or Spanner are changing tablet compression settings or tuning compaction more aggressively. Edit: given the mention of a job that got stopped, perhaps they had a tool that manually forced compaction of data in order to adopt new compression settings or purge deleted rows. Normally, compactions would happen on the tablet servers on a cycle of N days. Another possible explanation is that they tweaked the garbage collector, which runs on the master.