Snapshots for distributed object-based datastores

A distributed computer system comprising:

• a metadata database configured to be instantiable and to store map data for an object-based datastore, the map data locating respective data blocks for a given object key of the object-based datastore;
• and
• one or more manager nodes configured to perform operations comprising:
• in response to an access request that specifies a particular object key for an active timepoint, using a first instance of the metadata database to locate the respective data blocks for the particular object key at the active timepoint;
• in response to a snapshot request for a snapshot timepoint, wherein the snapshot timepoint is a temporal identifier of a second instance of the metadata database, instantiating, based on the snapshot timepoint, the second instance of the metadata database using the first instance of the metadata database, wherein the second instance represents a snapshot image of the object-based datastore for the snapshot timepoint;
• receiving a deletion request to delete the snapshot image;
• subsequent to deleting the snapshot image, (1) generating a first set of different object keys based on a first set of object keys associated with the snapshot image and a second set of object keys associated with a preceding snapshot image from a snapshot chain and (2) generating a second set of different object keys based on the first set of object keys and a third set of object keys associated with a subsequent snapshot image from the snapshot chain;
• and
• generating a set of reclaimable object keys by determining an intersection of the first set of different object keys and the second set of different object keys.

A computer-implemented method comprising:

• receiving, by one or more computing nodes, an access request that specifies a particular object key and a particular timepoint, wherein the particular timepoint is a temporal identifier of a first instance of an instantiable metadata datastore, and wherein the particular timepoint is different than a present timepoint;
• based on the particular timepoint, selecting, by the one or more computing nodes, a second instance of the instantiable metadata datastore that is associated with the particular timepoint;
• using, by the one or more computing nodes, the second instance of the instantiable metadata datastore to locate one or more distributed data blocks that were mapped to the particular object key during the particular timepoint;
• receiving a deletion request to delete the second instance of the instantiable metadata datastore;
• subsequent to deleting the second instance of the instantiable metadata datastore, (1) generating a first set of different object keys based on a first set of object keys associated with the second instance of the instantiable metadata datastore and a second set of object keys associated with a preceding instance of the instantiable metadata datastore and (2) generating a second set of different object keys based on the first set of object keys and a third set of object keys associated with a subsequent instance of the instantiable metadata datastore;
• and
• generating a set of reclaimable object keys by determining an intersection of the first set of different object keys and the second set of different object keys.