Update README.md

Author: Tinitto

CHANGELOG.md

@@ -7,15 +7,25 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+## [0.0.7] - 2022-11-9
+
+### Added
+
+- More thorough documentation for the Store
+
+### Changed
+
+### Fixed
+
 ## [0.0.6] - 2022-11-9
 
 ### Added
 
 ### Changed
 
-- Optimized the Compact operation. 
-  - Removed unnecessary internal type conversions e.g. to `internal.entries.Index`.
-  - Got rid of message passing in iterating over the index blocks
+- Optimized the Compact operation.
+    - Removed unnecessary internal type conversions e.g. to `internal.entries.Index`.
+    - Got rid of message passing in iterating over the index blocks
 
 ### Fixed
 

README.md

@@ -6,7 +6,7 @@ A very simple and fast key-value pure-go store but persisting data to disk, with
 
 This is the pure-golang version of the original [scdb](https://github.com/sopherapps/scdb)
 
-**scdb may not be production-ready yet. It works, quite well but it requires more vigorous testing.**
+**scdb may not be production-ready yet. It works, quite well but it requires more rigorous testing.**
 
 ## Purpose
 

scdb/store.go

@@ -12,13 +12,16 @@ import (
 	"time"
 )
 
-// DefaultDbFile is the default name of the database file that contains all the key-value pairs
-const DefaultDbFile string = "dump.scdb"
+// defaultDbFile is the default name of the database file that contains all the key-value pairs
+const defaultDbFile string = "dump.scdb"
 
-var ZeroU64 = internal.Uint64ToByteArray(0)
+var zeroU64 = internal.Uint64ToByteArray(0)
 
-// Store is the public interface to the key-value store
-// that allows us to do operations like Set, Get, Delete, Clear and Compact
+// Store is a key-value store that persists key-value pairs to disk
+//
+// Store behaves like a HashMap that saves keys and value as byte arrays
+// on disk. It allows for specifying how long each key-value pair should be
+// kept for i.e. the time-to-live in seconds. If None is provided, they last indefinitely.
 type Store struct {
 	bufferPool *buffers.BufferPool
 	header     *entries.DbFileHeader
@@ -27,14 +30,48 @@ type Store struct {
 	isClosed   bool
 }
 
-// New creates a new Store at the given path, with the given `compactionInterval`
+// New creates a new Store at the given path
+// The Store has a number of configurations that are passed into this New function
+//
+//   - `storePath` - required:
+//     The path to a directory where scdb should store its data
+//
+//   - `maxKeys` - default: 1 million:
+//     The maximum number of key-value pairs to store in store
+//
+//   - `redundantBlocks` - default: 1:
+//     The store has an index to hold all the keys. This index is split
+//     into a fixed number of blocks basing on the virtual memory page size
+//     and the total number of keys to be held i.e. `max_keys`.
+//     Sometimes, there may be hash collision errors as the store's
+//     current stored keys approach `max_keys`. The closer it gets, the
+//     more it becomes likely see those errors. Adding redundant blocks
+//     helps mitigate this. Just be careful to not add too many (i.e. more than 2)
+//     since the higher the number of these blocks, the slower the store becomes.
+//
+//   - `poolCapacity` - default: 5:
+//     The number of buffers to hold in memory as cache's for the store. Each buffer
+//     has the size equal to the virtual memory's page size, usually 4096 bytes.
+//     Increasing this number will speed this store up but of course, the machine
+//     has a limited RAM. When this number increases to a value that clogs the RAM, performance
+//     suddenly degrades, and keeps getting worse from there on.
+//
+//   - `compactionInterval` - default 3600s (1 hour):
+//     The interval at which the store is compacted to remove dangling
+//     keys. Dangling keys result from either getting expired or being deleted.
+//     When a `delete` operation is done, the actual key-value pair
+//     is just marked as `deleted` but is not removed.
+//     Something similar happens when a key-value is updated.
+//     A new key-value pair is created and the old one is left unindexed.
+//     Compaction is important because it reclaims this space and reduces the size
+//     of the database file.
 func New(path string, maxKeys *uint64, redundantBlocks *uint16, poolCapacity *uint64, compactionInterval *uint32) (*Store, error) {
 	err := os.MkdirAll(path, 0755)
 	if err != nil {
 		return nil, err
 	}
 
-	dbFilePath := filepath.Join(path, DefaultDbFile)
+	dbFilePath := filepath.Join(path, defaultDbFile)
 	bufferPool, err := buffers.NewBufferPool(poolCapacity, dbFilePath, maxKeys, redundantBlocks, nil)
 	if err != nil {
 		return nil, err
@@ -133,7 +170,7 @@ func (s *Store) Get(k []byte) ([]byte, error) {
 			return nil, err
 		}
 
-		if bytes.Equal(kvOffsetInBytes, ZeroU64) {
+		if bytes.Equal(kvOffsetInBytes, zeroU64) {
 			continue
 		}
 
@@ -173,7 +210,7 @@ func (s *Store) Delete(k []byte) error {
 			return err
 		}
 
-		if bytes.Equal(kvOffsetInBytes, ZeroU64) {
+		if bytes.Equal(kvOffsetInBytes, zeroU64) {
 			continue
 		}
 

scdb/store_test.go

@@ -3,6 +3,7 @@ package scdb
 import (
 	"fmt"
 	"github.com/stretchr/testify/assert"
+	"log"
 	"os"
 	"path"
 	"runtime"
@@ -521,6 +522,84 @@ func BenchmarkStore_SetWithTtl(b *testing.B) {
 
 }
 
+func ExampleNew() {
+	var maxKeys uint64 = 1_000_000
+	var redundantBlocks uint16 = 1
+	var poolCapacity uint64 = 10
+	var compactionInterval uint32 = 1_800
+
+	store, err := New(
+		"testdb",
+		&maxKeys,
+		&redundantBlocks,
+		&poolCapacity,
+		&compactionInterval)
+	if err != nil {
+		log.Fatalf("error opening store: %s", err)
+	}
+	defer func() {
+		_ = store.Close()
+	}()
+}
+
+func ExampleStore_Set() {
+	store, err := New("testdb", nil, nil, nil, nil)
+	if err != nil {
+		log.Fatalf("error opening store: %s", err)
+	}
+	defer func() {
+		_ = store.Close()
+	}()
+
+	err = store.Set([]byte("foo"), []byte("bar"), nil)
+	if err != nil {
+		log.Fatalf("error setting key value without ttl: %s", err)
+	}
+
+	ttl := uint64(3_600)
+	err = store.Set([]byte("fake"), []byte("bear"), &ttl)
+	if err != nil {
+		log.Fatalf("error setting key value with ttl: %s", err)
+	}
+}
+
+func ExampleStore_Get() {
+	store, err := New("testdb", nil, nil, nil, nil)
+	if err != nil {
+		log.Fatalf("error opening store: %s", err)
+	}
+	defer func() {
+		_ = store.Close()
+	}()
+
+	err = store.Set([]byte("foo"), []byte("bar"), nil)
+	if err != nil {
+		log.Fatalf("error setting key value: %s", err)
+	}
+
+	value, err := store.Get([]byte("foo"))
+	if err != nil {
+		log.Fatalf("error getting key: %s", err)
+	}
+
+	fmt.Printf("%s", value)
+	// Output: bar
+}
+func ExampleStore_Delete() {
+	store, err := New("testdb", nil, nil, nil, nil)
+	if err != nil {
+		log.Fatalf("error opening store: %s", err)
+	}
+	defer func() {
+		_ = store.Close()
+	}()
+
+	err = store.Delete([]byte("foo"))
+	if err != nil {
+		log.Fatalf("error deleting key: %s", err)
+	}
+}
+
 // removeStore is a utility to remove the old store just before a given test is run
 func removeStore(t *testing.T, path string) {
 	err := os.RemoveAll(path)