Key | Default | Type | Description
--- | --- | --- | ---

##### state.backend.forst.block.blocksize

4 kb

MemorySize

The approximate size (in bytes) of user data packed per block. The default blocksize is '4KB'.

##### state.backend.forst.block.cache-size

8 mb

MemorySize

The amount of the cache for data blocks in ForSt. The default block-cache size is '8MB'.

##### state.backend.forst.block.metadata-blocksize

4 kb

MemorySize

Approximate size of partitioned metadata packed per block. Currently applied to indexes block when partitioned index/filters option is enabled. The default blocksize is '4KB'.

##### state.backend.forst.bloom-filter.bits-per-key

10.0

Double

Bits per key that the bloom filter will use, this only takes effect when the bloom filter is used. The default value is 10.0.

##### state.backend.forst.bloom-filter.block-based-mode

false

Boolean

If set 'true', ForSt will use block-based filter instead of full filter, this only takes effect when bloom filter is used. The default value is 'false'.

##### state.backend.forst.compaction.filter.periodic-compaction-time

30 d

Duration

Periodic compaction could speed up expired state entries cleanup, especially for state entries rarely accessed. Files older than this value will be picked up for compaction, and re-written to the same level as they were before. It makes sure a file goes through compaction filters periodically. 0 means turning off periodic compaction.The default value is '30 d' (30 days).

##### state.backend.forst.compaction.filter.query-time-after-num-entries

1000

Long

Number of state entries to process by compaction filter before updating current timestamp. Updating the timestamp more often can improve cleanup speed, but it decreases compaction performance because it uses JNI calls from native code.The default value is '1000L'.

##### state.backend.forst.compaction.level.max-size-level-base

256 mb

MemorySize

The upper-bound of the total size of level base files in bytes. The default value is '256 mb'.

##### state.backend.forst.compaction.level.target-file-size-base

64 mb

MemorySize

The target file size for compaction, which determines a level-1 file size. The default value is '64 mb'.

##### state.backend.forst.compaction.level.use-dynamic-size

false

Boolean

If true, ForSt will pick target size of each level dynamically. From an empty key-value store, ForSt would make last level the base level, which means merging L0 data into the last level, until it exceeds max_bytes_for_level_base. And then repeat this process for second last level and so on. The default value is 'false'. For more information, please refer to RocksDB's doc.

##### state.backend.forst.compaction.style

LEVEL

Enum

The specified compaction style for DB. Candidate compaction style is LEVEL, FIFO, UNIVERSAL or NONE, and Flink chooses 'LEVEL' as default style.
Possible values:

- "LEVEL"
- "UNIVERSAL"
- "FIFO"
- "NONE"

##### state.backend.forst.compression.per.level

SNAPPY_COMPRESSION

List<Enum>

A semicolon-separated list of Compression Type. Different levels can have different compression policies. In many cases, lower levels use fast compression algorithms, while higher levels with more data use slower but more effective compression algorithms. The N th element in the List corresponds to the compression type of the level N-1. When `state.backend.forst.compaction.level.use-dynamic-size` is true, compression_per_level[0] still determines L0, but other elements are based on the base level and may not match the level seen in the info log.
Note: If the List size is smaller than the level number, the undefined lower level uses the last Compression Type in the List.
Some commonly used compression algorithms for candidates include `NO_COMPRESSION` ,`SNAPPY_COMPRESSION` and `LZ4_COMPRESSION`.
The default value is `SNAPPY_COMPRESSION`, which means that all data uses the Snappy compression algorithm. Likewise, if set to `NO_COMPRESSION` , means that all data is not compressed, which will achieve faster speed but will bring some space amplification. In addition, if we need to consider both spatial amplification and performance, we can also set it to '`NO_COMPRESSION`;`NO_COMPRESSION`;`LZ4_COMPRESSION`', which means that L0 and L1 data will not be compressed, and other data will be compressed using LZ4.
Possible values:

- "NO_COMPRESSION"
- "SNAPPY_COMPRESSION"
- "ZLIB_COMPRESSION"
- "BZLIB2_COMPRESSION"
- "LZ4_COMPRESSION"
- "LZ4HC_COMPRESSION"
- "XPRESS_COMPRESSION"
- "ZSTD_COMPRESSION"
- "DISABLE_COMPRESSION_OPTION"

##### state.backend.forst.files.open

-1

Integer

The maximum number of open files (per stateful operator) that can be used by the ForSt, '-1' means no limit. The default value is '-1'.

##### state.backend.forst.log.dir

(none)

String

The directory for ForSt's information logging files. If empty (Flink default setting), log files will be in the same directory as the Flink log. If non-empty, this directory will be used and the data directory's absolute path will be used as the prefix of the log file name. If setting this option as a non-existing location, e.g '/dev/null', ForSt will then create the log under its own database folder.

##### state.backend.forst.log.file-num

4

Integer

The maximum number of files ForSt should keep for information logging (Default setting: 4).

##### state.backend.forst.log.level

INFO_LEVEL

Enum

The specified information logging level for ForSt. If unset, Flink will use `INFO_LEVEL`.
Note: ForSt info logs will not be written to the TaskManager logs and there is no rolling strategy, unless you configure `state.backend.forst.log.dir`, `state.backend.forst.log.max-file-size`, and `state.backend.forst.log.file-num` accordingly. Without a rolling strategy, long-running tasks may lead to uncontrolled disk space usage if configured with increased log levels!
There is no need to modify the ForSt log level, unless for troubleshooting ForSt.
Possible values:

- "DEBUG_LEVEL"
- "INFO_LEVEL"
- "WARN_LEVEL"
- "ERROR_LEVEL"
- "FATAL_LEVEL"
- "HEADER_LEVEL"
- "NUM_INFO_LOG_LEVELS"

##### state.backend.forst.log.max-file-size

25 mb

MemorySize

The maximum size of ForSt's file used for information logging. If the log files becomes larger than this, a new file will be created. If 0, all logs will be written to one log file. The default maximum file size is '25MB'.

##### state.backend.forst.rescaling.use-delete-files-in-range

false

Boolean

If true, during rescaling, the deleteFilesInRange API will be invoked to clean up the useless key-values so that primary storage space can be reclaimed more promptly.

##### state.backend.forst.restore-overlap-fraction-threshold

0.0

Double

The threshold of overlap fraction between the state handle's key-group range and target key-group range. When restore base DB, only the handle which overlap fraction greater than or equal to threshold has a chance to be an initial handle. The default value is 0.0, there is always a handle will be selected for initialization.

##### state.backend.forst.thread.num

2

Integer

The maximum number of concurrent background flush and compaction jobs (per stateful operator). The default value is '2'.

##### state.backend.forst.use-bloom-filter

false

Boolean

Whether every newly created SST file will contain a Bloom filter. Default 'false'.

##### state.backend.forst.use-ingest-db-restore-mode

false

Boolean

A recovery mode that directly clips and ingests multiple DBs during state recovery if the keys in the SST files does not exceed the declared key-group range.

##### state.backend.forst.write-batch-size

2 mb

MemorySize

The max size of the consumed memory for ForSt batch write, will flush just based on item count if this config set to 0.

##### state.backend.forst.writebuffer.count

2

Integer

The maximum number of write buffers that are built up in memory. The default value is '2'.

##### state.backend.forst.writebuffer.number-to-merge

1

Integer

The minimum number of write buffers that will be merged together before writing to storage. The default value is '1'.

##### state.backend.forst.writebuffer.size

64 mb

MemorySize

The amount of data built up in memory (backed by an unsorted log on disk) before converting to a sorted on-disk files. The default writebuffer size is '64MB'.