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@@ -374,7 +374,45 @@ For more information on getting started with Bolt, check out the following artic -## Comparing Bolt to LMDB +## Comparison with other databases + +### Postgres, MySQL, & other relational databases + +Relational databases structure data into rows and are only accessible through +the use of SQL. This approach provides flexibility in how you store and query +your data but also incurs overhead in parsing and planning SQL statements. Bolt +accesses all data by a byte slice key. This makes Bolt fast to read and write +data by key but provides no built-in support for joining values together. + +Most relational databases (with the exception of SQLite) are standalone servers +that run separately from your application. This gives your systems +flexibility to connect multiple application servers to a single database +server but also adds overhead in serializing and transporting data over the +network. Bolt runs as a library included in your application so all data access +has to go through your application's process. This brings data closer to your +application but limits multi-process access to the data. + + +### LevelDB, RocksDB + +LevelDB and it's derivatives (RocksDB, HyperLevelDB) are similar to Bolt in that +they are libraries bundled into the application, however, their underlying +structure is a log-structured merge-tree (LSM tree). An LSM tree optimizes +random writes by using a write ahead log and multi-tiered, sorted files called +SSTables. Bolt uses a B+tree internally and only a single file. Both approaches +have trade offs. + +If you require a high random write throughput (>10,000 w/sec) or you need to use +spinning disks then LevelDB could be a good choice. If your application is +read-heavy or does a lot of range scans then Bolt could be a good choice. + +One other important consideration is that LevelDB does not have transactions. +It supports batch writing of key/values pairs and it supports read snapshots +but it will not give you the ability to do a compare-and-swap operation safely. +Bolt supports fully serializable ACID transactions. + + +### LDMB Bolt was originally a port of LMDB so it is architecturally similar. Both use a B+tree, have ACID semanetics with fully serializable transactions, and support @@ -386,6 +424,11 @@ several unsafe actions such as direct writes and append writes for the sake of performance. Bolt opts to disallow actions which can leave the database in a corrupted state. The only exception to this in Bolt is `DB.NoSync`. +There are also a few differences in API. LMDB requires a maximum mmap size when +opening an `mdb_env` whereas Bolt will handle incremental mmap resizing +automatically. LMDB overloads the getter and setter functions with multiple +flags whereas Bolt splits these specialized cases into their own functions. + ## Caveats & Limitations |