bolt-内嵌kv存储

However, this limited scope also means that the project is complete.

more featureful version repo

关于transactions的手动实现

// Start a writable transaction.
tx, err := db.Begin(true)
if err != nil {
    return err
}
defer tx.Rollback()

// Use the transaction...
_, err := tx.CreateBucket([]byte("MyBucket"))
if err != nil {
    return err
}

// Commit the transaction and check for error.
if err := tx.Commit(); err != nil {
    return err
}

使用bucket部分

这里面比较有意思的是：通过seek()部分操作

prefix scans
range scans
foreach

天然支持database backups

comparison with other databases

Postgres, MySQL, & other relational databases

sql

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. 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

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.

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.(事务上的支持)

LMDB

Bolt was originally a port of LMDB so it is architecturally similar. Both use a B+tree, have ACID semantics with fully serializable transactions, and support lock-free MVCC using a single writer and multiple readers.

on safe actions

on api, LMDB requires a maximum mmap size when opening an mdb_env whereas Bolt will handle incremental mmap resizing automatically

conclusion

Bolt is good for read intensive workloads.
Bolt uses a B+tree internally so there can be a lot of random page access
Bulk loading a lot of random writes into a new bucket can be slow as the page will not split until the transaction is committed. 在一个事务里尽量是连续性的操作
The data structures in the Bolt database are memory mapped so the data file will be endian specific
Because of the way pages are laid out on disk, Bolt cannot truncate data files and return free pages back to the disk. Instead, Bolt maintains a free list of unused pages within its data file. These free pages can be reused by later transactions. 关于bolt的reuse特性