Snapshots for distributed object-based datastores

A distributed computer system comprising:

• a plurality of data nodes communicatively coupled with one another and implementing an object-based datastore for a plurality of object keys, wherein an object key is a lexicographic identifier that names a particular data object and that is reclaimable upon deletion of the particular data object and a set of data blocks associated with the particular data object;
• a metadata database configured to be instantiable and to store map data for the 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 a first 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 data object key at the active timepoint, wherein the first instance is configured to be modifiable to update a respective map data for a present 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, the second instance preserving a read-only copy of the first instance at the snapshot timepoint, wherein the second instance represents a snapshot image of the object-based datastore for the snapshot timepoint;
• in response to a second access request that specifies the particular object key for the snapshot timepoint, using the second instance of the metadata database to locate the respective data blocks that were associated with the particular object key at 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:

• generating, by one or more computing nodes of a distributed computing platform, a plurality of instances of an instantiable metadata datastore associated with an object-based datastore, wherein (i) a first instance of the instantiable metadata datastore is configured to dynamically identify distributed data blocks that are mapped to object keys of the object-based datastore at a present timepoint, and (ii) one or more other instances of the instantiable metadata datastore each configured to preserve a read-only copy of the first instance at a respective timepoint prior to the present timepoint,
• receiving, by the 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 an instance of the instantiable metadata datastore, and wherein the particular timepoint is different than the present timepoint;
• based on the particular timepoint, selecting, by the one or more computing nodes, a particular instance of the one or more other instances of the instantiable metadata datastore that is associated with the particular timepoint;
• handling, by the one or more computing nodes, the access request based on using the particular instance of the instantiable metadata datastore to locate the distributed data blocks that were mapped to the particular object key during the particular timepoint;
• receiving a deletion request to delete the particular instance of the instantiable metadata datastore;
• subsequent to deleting the particular 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 particular 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.