opt

type Cacher interface {
	New(capacity int) cache.Cacher
}

type Compression uint

type Options struct {
	// AltFilters defines one or more 'alternative filters'.
	// 'alternative filters' will be used during reads if a filter block
	// does not match with the 'effective filter'.
	//
	// The default value is nil
	AltFilters []filter.Filter

	// BlockCacher provides cache algorithm for LevelDB 'sorted table' block caching.
	// Specify NoCacher to disable caching algorithm.
	//
	// The default value is LRUCacher.
	BlockCacher Cacher

	// BlockCacheCapacity defines the capacity of the 'sorted table' block caching.
	// Use -1 for zero, this has same effect as specifying NoCacher to BlockCacher.
	//
	// The default value is 8MiB.
	BlockCacheCapacity int

	// BlockCacheEvictRemoved allows enable forced-eviction on cached block belonging
	// to removed 'sorted table'.
	//
	// The default if false.
	BlockCacheEvictRemoved bool

	// BlockRestartInterval is the number of keys between restart points for
	// delta encoding of keys.
	//
	// The default value is 16.
	BlockRestartInterval int

	// BlockSize is the minimum uncompressed size in bytes of each 'sorted table'
	// block.
	//
	// The default value is 4KiB.
	BlockSize int

	// CompactionExpandLimitFactor limits compaction size after expanded.
	// This will be multiplied by table size limit at compaction target level.
	//
	// The default value is 25.
	CompactionExpandLimitFactor int

	// CompactionGPOverlapsFactor limits overlaps in grandparent (Level + 2) that a
	// single 'sorted table' generates.
	// This will be multiplied by table size limit at grandparent level.
	//
	// The default value is 10.
	CompactionGPOverlapsFactor int

	// CompactionL0Trigger defines number of 'sorted table' at level-0 that will
	// trigger compaction.
	//
	// The default value is 4.
	CompactionL0Trigger int

	// CompactionSourceLimitFactor limits compaction source size. This doesn't apply to
	// level-0.
	// This will be multiplied by table size limit at compaction target level.
	//
	// The default value is 1.
	CompactionSourceLimitFactor int

	// CompactionTableSize limits size of 'sorted table' that compaction generates.
	// The limits for each level will be calculated as:
	//   CompactionTableSize * (CompactionTableSizeMultiplier ^ Level)
	// The multiplier for each level can also fine-tuned using CompactionTableSizeMultiplierPerLevel.
	//
	// The default value is 2MiB.
	CompactionTableSize int

	// CompactionTableSizeMultiplier defines multiplier for CompactionTableSize.
	//
	// The default value is 1.
	CompactionTableSizeMultiplier float64

	// CompactionTableSizeMultiplierPerLevel defines per-level multiplier for
	// CompactionTableSize.
	// Use zero to skip a level.
	//
	// The default value is nil.
	CompactionTableSizeMultiplierPerLevel []float64

	// CompactionTotalSize limits total size of 'sorted table' for each level.
	// The limits for each level will be calculated as:
	//   CompactionTotalSize * (CompactionTotalSizeMultiplier ^ Level)
	// The multiplier for each level can also fine-tuned using
	// CompactionTotalSizeMultiplierPerLevel.
	//
	// The default value is 10MiB.
	CompactionTotalSize int

	// CompactionTotalSizeMultiplier defines multiplier for CompactionTotalSize.
	//
	// The default value is 10.
	CompactionTotalSizeMultiplier float64

	// CompactionTotalSizeMultiplierPerLevel defines per-level multiplier for
	// CompactionTotalSize.
	// Use zero to skip a level.
	//
	// The default value is nil.
	CompactionTotalSizeMultiplierPerLevel []float64

	// Comparer defines a total ordering over the space of []byte keys: a 'less
	// than' relationship. The same comparison algorithm must be used for reads
	// and writes over the lifetime of the DB.
	//
	// The default value uses the same ordering as bytes.Compare.
	Comparer comparer.Comparer

	// Compression defines the 'sorted table' block compression to use.
	//
	// The default value (DefaultCompression) uses snappy compression.
	Compression Compression

	// DisableBufferPool allows disable use of util.BufferPool functionality.
	//
	// The default value is false.
	DisableBufferPool bool

	// DisableBlockCache allows disable use of cache.Cache functionality on
	// 'sorted table' block.
	//
	// The default value is false.
	DisableBlockCache bool

	// DisableCompactionBackoff allows disable compaction retry backoff.
	//
	// The default value is false.
	DisableCompactionBackoff bool

	// DisableLargeBatchTransaction allows disabling switch-to-transaction mode
	// on large batch write. If enable batch writes large than WriteBuffer will
	// use transaction.
	//
	// The default is false.
	DisableLargeBatchTransaction bool

	// DisableSeeksCompaction allows disabling 'seeks triggered compaction'.
	// The purpose of 'seeks triggered compaction' is to optimize database so
	// that 'level seeks' can be minimized, however this might generate many
	// small compaction which may not preferable.
	//
	// The default is false.
	DisableSeeksCompaction bool

	// ErrorIfExist defines whether an error should returned if the DB already
	// exist.
	//
	// The default value is false.
	ErrorIfExist bool

	// ErrorIfMissing defines whether an error should returned if the DB is
	// missing. If false then the database will be created if missing, otherwise
	// an error will be returned.
	//
	// The default value is false.
	ErrorIfMissing bool

	// Filter defines an 'effective filter' to use. An 'effective filter'
	// if defined will be used to generate per-table filter block.
	// The filter name will be stored on disk.
	// During reads LevelDB will try to find matching filter from
	// 'effective filter' and 'alternative filters'.
	//
	// Filter can be changed after a DB has been created. It is recommended
	// to put old filter to the 'alternative filters' to mitigate lack of
	// filter during transition period.
	//
	// A filter is used to reduce disk reads when looking for a specific key.
	//
	// The default value is nil.
	Filter filter.Filter

	// IteratorSamplingRate defines approximate gap (in bytes) between read
	// sampling of an iterator. The samples will be used to determine when
	// compaction should be triggered.
	// Use negative value to disable iterator sampling.
	// The iterator sampling is disabled if DisableSeeksCompaction is true.
	//
	// The default is 1MiB.
	IteratorSamplingRate int

	// NoSync allows completely disable fsync.
	//
	// The default is false.
	NoSync bool

	// NoWriteMerge allows disabling write merge.
	//
	// The default is false.
	NoWriteMerge bool

	// OpenFilesCacher provides cache algorithm for open files caching.
	// Specify NoCacher to disable caching algorithm.
	//
	// The default value is LRUCacher.
	OpenFilesCacher Cacher

	// OpenFilesCacheCapacity defines the capacity of the open files caching.
	// Use -1 for zero, this has same effect as specifying NoCacher to OpenFilesCacher.
	//
	// The default value is 200 on MacOS and 500 on other.
	OpenFilesCacheCapacity int

	// If true then opens DB in read-only mode.
	//
	// The default value is false.
	ReadOnly bool

	// Strict defines the DB strict level.
	Strict Strict

	// WriteBuffer defines maximum size of a 'memdb' before flushed to
	// 'sorted table'. 'memdb' is an in-memory DB backed by an on-disk
	// unsorted journal.
	//
	// LevelDB may held up to two 'memdb' at the same time.
	//
	// The default value is 4MiB.
	WriteBuffer int

	// WriteL0StopTrigger defines number of 'sorted table' at level-0 that will
	// pause write.
	//
	// The default value is 12.
	WriteL0PauseTrigger int

	// WriteL0SlowdownTrigger defines number of 'sorted table' at level-0 that
	// will trigger write slowdown.
	//
	// The default value is 8.
	WriteL0SlowdownTrigger int

	// FilterBaseLg is the log size for filter block to create a bloom filter.
	//
	// The default value is 11(as well as 2KB)
	FilterBaseLg int

	// MaxManifestFileSize is the maximum size limit of the MANIFEST-****** file.
	// When the MANIFEST-****** file grows beyond this size, LevelDB will create
	// a new MANIFEST file.
	//
	// The default value is 64 MiB.
	MaxManifestFileSize int64
}

type ReadOptions struct {
	// DontFillCache defines whether block reads for this 'read operation'
	// should be cached. If false then the block will be cached. This does
	// not affects already cached block.
	//
	// The default value is false.
	DontFillCache bool

	// Strict will be OR'ed with global DB 'strict level' unless StrictOverride
	// is present. Currently only StrictReader that has effect here.
	Strict Strict
}

type Strict uint

type WriteOptions struct {
	// NoWriteMerge allows disabling write merge.
	//
	// The default is false.
	NoWriteMerge bool

	// Sync is whether to sync underlying writes from the OS buffer cache
	// through to actual disk, if applicable. Setting Sync can result in
	// slower writes.
	//
	// If false, and the machine crashes, then some recent writes may be lost.
	// Note that if it is just the process that crashes (and the machine does
	// not) then no writes will be lost.
	//
	// In other words, Sync being false has the same semantics as a write
	// system call. Sync being true means write followed by fsync.
	//
	// The default value is false.
	Sync bool
}