Minimal Perfect Hash Tables are an immutable key/value store with efficient space utilization and fast reads. They are ideal for the use-case of tables built by batch processes and shipped to multiple servers.
Indeed MPH is available on Maven Central, just add the following dependency:
<dependency>
<groupId>com.indeed</groupId>
<artifactId>mph-table</artifactId>
<version>1.0.4</version>
</dependency>
The primary interfaces are TableReader, to construct a reader to an existing table, TableWriter, to build a table, and TableConfig, to specify the configuration for the writer.
How to write a table:
final TableConfig<Long, Long> config = new TableConfig()
.withKeySerializer(new SmartLongSerializer())
.withValueSerializer(new SmartVLongSerializer());
final Set<Pair<Long, Long>> entries = new HashSet<>();
for (long i = 0; i < 20; ++i) {
entries.add(new Pair(i, i * i));
}
TableWriter.write(new File("squares"), config, entries);How to read a table:
try (final TableReader<Long, Long> reader = TableReader.open("squares")) {
final Long value = reader.get(3L); // get one
for (final Pair<Long, Long> p : reader) { // iterate over all
...
}
}In addition to the Java API, TableReader and TableWriter provide convenience command-line interfaces to read and write tables, allowing you to quickly get started without writing any code:
# print all key-values in a table as TSV
$ java com.indeed.mph.TableReader --dump <table>
# print the value for a single key
$ java com.indeed.mph.TableReader --get <key> <table>
# create a table from a TSV file of words with counts
$ java com.indeed.mph.TableWriter --valueSerializer .SmartVLongSerializer <table to create> <counts.tsv>
# create a table from a TSV file mapping movie ids to lists of actor names (compressed by reference)
$ java com.indeed.mph.TableWriter --keySerializer .SmartVLongSerializer --valueSerializer '.SmartListSerializer(.SmartDictionarySerializer)' <table to create> <movies.tsv>
# same as above, not actually storing the movie ids but still allowing retrieval by them
$ java com.indeed.mph.TableWriter --keyStorage IMPLICIT --keySerializer .SmartVLongSerializer --valueSerializer '.SmartListSerializer(.SmartDictionarySerializer)' <table to create> <movies.tsv>
This project is governed by the Contributor Covenant v 1.4.1
This project is licensed under the Apache-2.0 License - see the LICENSE file for details.