Documentation: added a doc for bbolt command-line.

cmd/bbolt/README.md

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+# Introduction to bbolt command line
+
+`bbolt` provides a command line utility for inspecting and manipulating bbolt database files. To install bbolt command-line please refer [here](https://github.com/etcd-io/bbolt#installing)
+
+**Note**: [etcd](https://github.com/etcd-io/etcd) uses bbolt as its backend storage engine. In this document, we take etcd as an example to demonstrate the usage of bbolt commands. Refer to [install etcd](https://etcd.io/docs/v3.5/install/) for installing etcd.
+
+1. Start a single member etcd cluster with this command below:
+
+    ```bash
+    $etcd
+    ```
+
+    It will create a directory `default.etcd` by default under current working directory, and the directory structure will look like this:
+
+    ```bash
+    $tree default.etcd
+    default.etcd
+    └── member
+        ├── snap
+        │   └── db // this is bbolt database file
+        └── wal
+            └── 0000000000000000-0000000000000000.wal
+
+    3 directories, 2 files
+    ```
+
+2. Put some dummy data using [etcdctl](https://github.com/etcd-io/etcd/tree/main/etcdctl).
+3. Stop the etcd instance. Note a bbolt database file can only be opened by one read-write process, because it is exclusively locked when opened.
+
+## Usage
+
+- `bbolt command [arguments]`
+
+### help
+
+- help will print information about that command
+
+  ```bash
+  $bbolt help
+
+  The commands are:
+
+      bench       run synthetic benchmark against bbolt
+      buckets     print a list of buckets
+      check       verifies integrity of bbolt database
+      compact     copies a bbolt 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
+      surgery     perform surgery on bbolt database
+  ```
+
+- you can use `help` with any command: `bbolt [command] -h` for more information about command.
+
+## Analyse bbolt database with bbolt command line
+
+### info
+
+- `info` print the basic information about the given Bbolt database.
+- usage:
+  `bbolt info [path to the bbolt database]`
+
+    Example:
+
+    ```bash
+    $bbolt info ~/default.etcd/member/snap/db
+    Page Size: 4096
+    ```
+
+  - **note**: page size is given in bytes
+  - Bbolt database is using page size of 4KB
+
+### buckets
+
+- `buckets` print a list of buckets of Bbolt database is currently having. Find more information on buckets [here](https://github.com/etcd-io/bbolt#using-buckets)
+- usage:
+  `bbolt buckets [path to the bbolt database]`
+
+    Example:
+
+    ```bash
+    $bbolt buckets ~/default.etcd/member/snap/db
+    alarm
+    auth
+    authRoles
+    authUsers
+    cluster
+    key
+    lease
+    members
+    members_removed
+    meta
+    ```
+
+  - It means when you start an etcd, it creates these `10` buckets using bbolt database.
+
+### check
+
+- `check` opens a database at a given `[PATH]` and runs an exhaustive check to verify that all pages are accessible or are marked as freed. It also verifies that no pages are double referenced.
+- usage:
+  `bbolt check [path to the bbolt database]`
+
+    Example:
+
+    ```bash
+    $bbolt check ~/default.etcd/member/snap/db
+    ok
+    ```
+
+  - It returns `ok` as our database file `db` is not corrupted.
+
+### stats
+
+- To gather essential statistics about the bbolt database: `stats` performs an extensive search of the database to track every page reference. It starts at the current meta page and recursively iterates through every accessible bucket.
+- usage:
+  `bbolt stats [path to the bbolt database]`
+
+  Example:
+
+  ```bash
+  $bbolt stats ~/default.etcd/member/snap/db
+  Aggregate statistics for 10 buckets
+
+  Page count statistics
+      Number of logical branch pages: 0
+      Number of physical branch overflow pages: 0
+      Number of logical leaf pages: 0
+      Number of physical leaf overflow pages: 0
+  Tree statistics
+      Number of keys/value pairs: 11
+      Number of levels in B+tree: 1
+  Page size utilization
+      Bytes allocated for physical branch pages: 0
+      Bytes actually used for branch data: 0 (0%)
+      Bytes allocated for physical leaf pages: 0
+      Bytes actually used for leaf data: 0 (0%)
+  Bucket statistics
+      Total number of buckets: 10
+      Total number on inlined buckets: 10 (100%)
+      Bytes used for inlined buckets: 780 (0%)
+  ```
+
+### pages
+
+- Pages prints a table of pages with their type (meta, leaf, branch, freelist).
+- The `meta` will store the metadata information of database.
+- The `leaf` and `branch` pages will show a key count in the `items` column.
+- The `freelist` will show the number of free pages, which are free for writing again.
+- The `overflow` column shows the number of blocks that the page spills over into.
+- usage:
+  `bbolt pages [path to the bbolt database]`
+
+  Example:
+
+  ```bash
+  $bbolt pages ~/default.etcd/member/snap/db
+  ID       TYPE       ITEMS  OVRFLW
+  ======== ========== ====== ======
+  0        meta       0
+  1        meta       0
+  2        free
+  3        leaf       10
+  4        freelist   2
+  5        free
+  ```
+
+### page
+
+- Page prints one or more pages in human readable format.
+- usage:
+
+  ```bash
+  bolt page [path to the bbolt database] pageid [pageid...]
+  or: bolt page --all [path to the bbolt database]
+
+  Additional options include:
+
+  --all
+    prints all pages (only skips pages that were considered successful overflow pages)
+  --format-value=auto|ascii-encoded|hex|bytes|redacted (default: auto)
+    prints values (on the leaf page) using the given format
+  ```
+
+  Example:
+
+  ```bash
+  $bbolt page ~/default.etcd/member/snap/db 3
+  Page ID:    3
+  Page Type:  leaf
+  Total Size: 4096 bytes
+  Overflow pages: 0
+  Item Count: 10
+
+  "alarm": <pgid=0,seq=0>
+  "auth": <pgid=0,seq=0>
+  "authRoles": <pgid=0,seq=0>
+  "authUsers": <pgid=0,seq=0>
+  "cluster": <pgid=0,seq=0>
+  "key": <pgid=0,seq=0>
+  "lease": <pgid=0,seq=0>
+  "members": <pgid=0,seq=0>
+  "members_removed": <pgid=0,seq=0>
+  "meta": <pgid=0,seq=0>
+  ```
+
+  - It prints information of page `page ID: 3`
+
+### page-item
+
+- page-item prints a page item's key and value.
+- usage:
+
+  ```bash
+  bolt page-item [options] [path to the bbolt database] <pageId> <itemId>
+  Additional options include:
+
+      --key-only
+          Print only the key
+      --value-only
+          Print only the value
+      --format
+          Output format. One of: auto|ascii-encoded|hex|bytes|redacted (default=ascii-encoded)
+  ```
+
+  Example:
+
+  ```bash
+  $bbolt page-item --key-only ~/default.etcd/member/snap/db 3 7
+  "members"
+  ```
+
+  - It returns the key as `--key-only` flag is passed of `pageID: 3` and `itemID: 7`
+
+### dump
+
+- Dump prints a hexadecimal dump of one or more given pages.
+- usage:
+  `bolt dump [path to the bbolt database] [pageid...]`
+
+### keys
+
+- Print a list of keys in the given bucket.
+- usage:
+
+  ```bash
+  bolt keys [path to the bbolt database] [BucketName]
+
+  Additional options include:
+  --format
+    Output format. One of: auto|ascii-encoded|hex|bytes|redacted (default=bytes)
+  ```
+
+  Example 1:
+
+  ```bash
+  $bbolt keys ~/default.etcd/member/snap/db meta
+  confState
+  consistent_index
+  term
+  ```
+
+  - It list all the keys in bucket: `meta`
+
+  Example 2:
+
+  ```bash
+  $bbolt keys ~/default.etcd/member/snap/db members
+  8e9e05c52164694d
+  ```
+
+  - It list all the keys in `members` bucket which is a `memberId` of etcd cluster member.
+  - In this case we are running a single member etcd cluster, hence only `one memberId` is present. If we would have run a `3` member etcd cluster then it will return a `3 memberId` as `3 cluster members` would have been present in `members` bucket.
+
+### get
+
+- Print the value of the given key in the given bucket.
+- usage:
+
+  ```bash
+  bolt get [path to the bbolt database] [BucketName] [Key]
+
+  Additional options include:
+  --format
+    Output format. One of: auto|ascii-encoded|hex|bytes|redacted (default=bytes)
+  --parse-format
+    Input format (of key). One of: ascii-encoded|hex (default=ascii-encoded)"
+  ```
+
+  Example 1:
+
+  ```bash
+  $bbolt get --format=hex ~/default.etcd/member/snap/db meta term
+  0000000000000004
+  ```
+
+  - It returns the value present in bucket: `meta` for key: `term` in hexadecimal format.
+
+  Example 2:
+
+  ```bash
+  $bbolt get ~/default.etcd/member/snap/db members 8e9e05c52164694d
+  {"id":10276657743932975437,"peerURLs":["http://localhost:2380"],"name":"default","clientURLs":["http://localhost:2379"]}
+  ```
+
+  - It returns the value present in bucket: `members` for key: `8e9e05c52164694d`.
+
+### compact
+
+- Compact opens a database at given `[Source Path]` and walks it recursively, copying keys as they are found from all buckets, to a newly created database at `[Destination Path]`. The original database is left untouched.
+- usage:
+
+  ```bash
+  bbolt compact [options] -o [Destination Path] [Source Path]
+
+  Additional options include:
+
+  -tx-max-size NUM
+    Specifies the maximum size of individual transactions.
+    Defaults to 64KB
+  ```
+
+  Example:
+
+  ```bash
+  $bbolt compact -o ~/db.compact ~/default.etcd/member/snap/db
+  16805888 -> 32768 bytes (gain=512.88x)
+  ```
+
+  - It will create a compacted database file: `db.compact` at given path.
+
+### bench
+
+- run synthetic benchmark against bbolt database.
+- usage:
+
+    ```bash
+    Usage:
+    -batch-size int
+
+    -blockprofile string
+
+    -count int
+            (default 1000)
+    -cpuprofile string
+
+    -fill-percent float
+            (default 0.5)
+    -key-size int
+            (default 8)
+    -memprofile string
+
+    -no-sync
+
+    -path string
+
+    -profile-mode string
+            (default "rw")
+    -read-mode string
+            (default "seq")
+    -value-size int
+            (default 32)
+    -work
+
+    -write-mode string
+            (default "seq")
+    ```
+
+    Example:
+
+    ```bash
+    $bbolt bench ~/default.etcd/member/snap/db -batch-size 400 -key-size 16
+    # Write	68.523572ms	(68.523µs/op)	(14593 op/sec)
+    # Read	1.000015152s	(11ns/op)	(90909090 op/sec)
+    ```
+
+  - It runs a benchmark with batch size of `400` and with key size of `16` while for others parameters default value is taken.