boltDB 是用 go 写的一款基于纯内存的 k-v 存储引擎，etcd 底层就使用了 boltDB。相对于其他常见的如 MySQL、redis 等，其实现的功能较简单，是一个很好的通过阅读源码，加强对数据库、操作系统文件处理等，以及 go 语言本身的理解。
组织结构
boltDB 代码不多，一般都是 test、main 以及一些平台兼容代码（为了兼容各个操作系统，统一封装了不同操作系统的一些系统调用），概览如下：
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> gocloc --by-file --include-lang=Go --exclude-ext=.go .
---------------------------------------------------------------------------------------
File files blank comment code
---------------------------------------------------------------------------------------
bucket_test.go 235 111 1613
cmd/bbolt/main.go 314 251 1571
db_test.go 213 147 1423
tx_test.go 101 74 749
db.go 173 306 695
cursor_test.go 97 65 655
bucket.go 120 162 495
tx.go 101 146 477
node.go 88 122 392
freelist_test.go 43 17 374
freelist.go 44 63 297
cursor.go 53 78 265
simulation_test.go 56 40 265
page.go 32 24 148
freelist_hmap.go 35 20 123
node_test.go 19 21 116
bolt_windows.go 20 19 102
quick_test.go 13 10 67
bolt_unix.go 12 15 66
bolt_unix_aix.go 12 13 65
bolt_unix_solaris.go 11 12 65
page_test.go 10 5 57
manydbs_test.go 12 2 53
simulation_no_freelist_sync_test.go 3 0 44
allocate_test.go 6 0 25
errors.go 17 30 24
bolt_openbsd.go 4 0 23
unsafe.go 5 14 20
bolt_linux.go 2 1 7
boltsync_unix.go 2 2 4
bolt_386.go 2 2 3
bolt_amd64.go 2 2 3
bolt_arm64.go 3 3 3
bolt_mips64x.go 3 3 3
bolt_mipsx.go 3 3 3
bolt_ppc.go 3 3 3
bolt_ppc64.go 3 3 3
bolt_ppc64le.go 3 3 3
bolt_riscv64.go 3 3 3
bolt_s390x.go 3 3 3
doc.go 13 30 1
---------------------------------------------------------------------------------------
TOTAL 41 1894 1828 10311
---------------------------------------------------------------------------------------
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bolt 主要文件大概 4k+ 行，其他形如 bolt_* 的文件：
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> wc -l `ls *.go | grep -iv bolt_ | grep -iv test | grep -iv doc | grep -iv unix`
777 bucket.go
400 cursor.go
1037 db.go
71 errors.go
252 freelist.go
604 node.go
197 page.go
691 tx.go
4029 total
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文件与目录组织结构如下：
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> tree
.
├── LICENSE
├── Makefile
├── README.md
├── allocate_test.go
├── bolt_386.go
├── bolt_amd64.go
├── bolt_arm.go
├── bolt_arm64.go
├── bolt_linux.go
├── bolt_mips64x.go
├── bolt_mipsx.go
├── bolt_openbsd.go
├── bolt_ppc.go
├── bolt_ppc64.go
├── bolt_ppc64le.go
├── bolt_riscv64.go
├── bolt_s390x.go
├── bolt_unix.go
├── bolt_unix_aix.go
├── bolt_unix_solaris.go
├── bolt_windows.go
├── boltsync_unix.go
├── bucket.go
├── bucket_test.go
├── cmd
│ └── bbolt
│ ├── main.go
│ └── main_test
├── cover.out
├── cursor.go
├── cursor_test.go
├── db.go
├── db_test.go
├── doc.go
├── errors.go
├── freelist.go
├── freelist_hmap.go
├── freelist_test.go
├── go.mod
├── go.sum
├── manydbs_test.go
├── node.go
├── node_test.go
├── page.go
├── page_test.go
├── quick_test.go
├── simulation_no_freelist_sync_test.go
├── simulation_test.go
├── tx.go
├── tx_test.go
└── unsafe.go
2 directories, 49 files
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其中，errors.go 定义的是全局错误，其他文件对应一个核心模块，后面会逐个注解。
cmd/bbolt/main.go 封装了 bolt 命令行参数，代码组织格式类似，实现了各大命令行的使用：
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> bbolt
Bolt is a tool for inspecting bolt databases.
Usage:
bolt command [arguments]
The commands are:
bench run synthetic benchmark against bolt
buckets print a list of buckets
check verifies integrity of bolt database
compact copies a bolt database, compacting it in the process
dump print a hexadecimal dump of a single page
get print the value of a key in a bucket
info print basic info
keys print a list of keys in a bucket
help print this screen
page print one or more pages in human readable format
pages print list of pages with their types
page-item print the key and value of a page item.
stats iterate over all pages and generate usage stats
Use "bolt [command] -h" for more information about a command.
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主要模块关系
db.open
Author
Liuduoyu
LastMod
2020-09-02
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