Speed up database loading

Turns out that slurping a 14MB file (offsets.sdb) during initialization
added 30s to the production server startup time lol. On my development
box, which has an old but real direct read-write SSD the cost of doing
this is negligible.

This patch simply memory maps the offsets file before reading so now
we're back to reasonable startup times in production.

Id: 18977bad80fc0a73a4c843ad1d4e16c43d78c4b0
Author: Caio
Commit time: 2019-05-22T08:53:14+02:00

Modified src/main/java/co/caio/cerberus/db/SimpleRecipeMetadataDatabase.java

@@ -1,5 +1,6
package co.caio.cerberus.db;

+import co.caio.cerberus.db.RecipeMetadataDatabase.RecipeMetadataDbException;
import co.caio.cerberus.flatbuffers.FlatRecipe;
import com.carrotsearch.hppc.LongIntHashMap;
import java.io.FileNotFoundException;

@@ -33,9 +34,12
throw new RecipeMetadataDbException("Not a directory: " + baseDir);
}

- try (var raf = new RandomAccessFile(baseDir.resolve(FILE_OFFSETS).toFile(), "r")) {
+ var offsetsPath = baseDir.resolve(FILE_OFFSETS);
+ try (var raf = new RandomAccessFile(offsetsPath.toFile(), "r")) {

- int size = raf.readInt();
+ var mapped = raf.getChannel().map(MapMode.READ_ONLY, 0, Files.size(offsetsPath));
+
+ int size = mapped.getInt();
if (size < 0) {
throw new RecipeMetadataDbException("Invalid offsets file length");
}

@@ -43,7 +47,7
idToOffset = new LongIntHashMap(size);

while (size-- > 0) {
- idToOffset.put(raf.readLong(), raf.readInt());
+ idToOffset.put(mapped.getLong(), mapped.getInt());
}

} catch (IOException e) {