Multiple transactions in a single KV store

A database system, comprising:

• processor, main memory, and secondary memory implementing:
• a plurality of low-level stores, each including key-value (KV) pairs and having a respective low-level running transaction accumulating a plurality of changes to the key-value pairs of the low-level store;
• and
• a top-level store including for each of the plurality of low-level stores information leading to the respective low-level store and information indicating which respective low-level running transaction was last committed in the low-level store, and has a top-level running transaction, distinct of a plurality of low-level running transactions of the plurality of low-level stores, accumulating a plurality of changes to the information indicating which respective low-level running transaction was last committed to a low-level store of the plurality of low-level stores;
• and
• a KV store database management system (DBMS) configured to:
• in response to a plurality of changes made to a plurality of key-value pairs in at least two of the plurality of low-level stores, such that each of the respective at least two low-level transactions of the at least two low-level stores accumulate some of the plurality of changes:
• commit the respective low-level running transaction of one of the at least two low-level stores, without committing another respective low-level transaction of another of the at least two low-level stores to reduce an amount of writes to secondary memory, by:
• persisting changes to the one low-level store accumulated by the respective low-level running transaction to secondary memory;
• and
• updating the top-level store to indicate the respective low-level running transaction was last committed in the one low-level store;
• and
• after committing the respective low-level running transaction of the one low-level store, open a new respective low-level transaction for the one low-level store.

A non-transitory, computer-readable storage medium encoded with instructions executable by a processor to implement a key-value (KV) store database management system (DBMS) to provide a KV store to an application, the instructions comprising:

• provide a plurality of low-level stores and a top-level store, wherein:
• each of the plurality of low-level stores includes key-value pairs and has a respective low-level running transaction accumulating a plurality of changes to the key-value pairs of the low-level store;
• and
• the top-level store includes for each of the plurality of low-level stores information leading to the respective low-level store and information indicating which respective low-level running transaction was last committed in the low-level store, and has a top-level running transaction, distinct of a plurality of low-level running transactions of the plurality of low-level stores, accumulating a plurality of changes to the information indicating which respective low-level running transaction was last committed to a low-level store of the plurality of low-level stores;
• and
• in response to a plurality of changes made to a plurality of key-value pairs in at least two of the plurality of low-level stores, such that each of the respective at least two low-level transactions of the at least two low-level stores accumulate some of the plurality of changes:
• commit the respective low-level running transaction of one of the at least two low-level stores, without committing another respective low-level transaction of another of the at least two low-level stores to reduce an amount of writes to secondary memory, comprising:
• persisting changes to the one low-level store accumulated by the respective low-level running transaction to secondary memory;
• and
• updating the top-level store to indicate the respective low-level running transaction was last committed in the one low-level store;
• and
• after committing the respective low-level running transaction of the one low-level store, opening a new respective low-level running transaction for the one low-level store.