dremio 包含一个强大的功能就是反射加速，dremio 为了对于反射数据的存储开发了自己的文件系统插件
插件类图
parquet 以及iceberg 的支持
从start 入口可以看出包含了不同的处理，实际上dremio 从21 版本开始就默认基于了iceberg 存储了（同时也需要分布式存储）
@Override
public void start() throws IOException {super.start();
// 同时还需要初始化MaterializationStore，主要是反射元数据的存储
materializationStore = new MaterializationStore(DirectProvider.<LegacyKVStoreProvider>wrap(getContext().getKVStoreProvider()));
formatPlugin = (ParquetFormatPlugin) formatCreator.getFormatPluginByConfig(new ParquetFormatConfig());
icebergFormatPlugin = (IcebergFormatPlugin)formatCreator.getFormatPluginByConfig(new IcebergFormatConfig());
}
插件对于不同数据的处理（主要是getDatasetHandle）
@Override
public Optional<DatasetHandle> getDatasetHandle(EntityPath datasetPath, GetDatasetOption... options) throws ConnectorException {// 反射数据存储有自己的格式约定，会进行判断，实际上只包含两部分
List<String> components = normalizeComponents(datasetPath.getComponents());
if (components == null) {return Optional.empty();
}
Preconditions.checkState(components.size() == 3, "Unexpected number of components in path");
ReflectionId reflectionId = new ReflectionId(components.get(1));
MaterializationId materializationId = new MaterializationId(components.get(2));
Materialization materialization = getMaterialization(materializationId);
if (materialization == null) {return Optional.empty();
}
FluentIterable<Refresh> refreshes = getSlices(materialization, reflectionId);
if(refreshes == null) {return Optional.empty();
}
final String selectionRoot = getConfig().getPath().resolve(refreshes.first().get().getReflectionId().getId()).toString();
BatchSchema currentSchema = CurrentSchemaOption.getSchema(options);
FileConfig fileConfig = FileConfigOption.getFileConfig(options);
List<String> sortColumns = SortColumnsOption.getSortColumns(options);
Integer fieldCount = MaxLeafFieldCount.getCount(options);
boolean icebergDataset = isUsingIcebergDataset(materialization);
final FileSelection selection = getFileSelection(refreshes, selectionRoot, icebergDataset);
final PreviousDatasetInfo pdi = new PreviousDatasetInfo(fileConfig, currentSchema, sortColumns, null, null, true);
if (!icebergDataset) {FileDatasetHandle.checkMaxFiles(datasetPath.getName(), selection.getFileAttributesList().size(), getContext(), getConfig().isInternal());
}
// 此方法包含了实际的处理，具体可以看源码，实际上就是对于parquet以及icegerg 数据集的处理，进行判断，使用不同的访问器
return getDatasetHandle(datasetPath, fieldCount, icebergDataset, selection, pdi);
}
参考资料
services/accelerator/src/main/java/com/dremio/service/reflection/materialization/AccelerationStoragePlugin.java
services/accelerator/src/main/java/com/dremio/service/reflection/materialization/AccelerationFileSystem.java
services/accelerator/src/main/java/com/dremio/service/reflection/materialization/AccelerationStoragePluginConfig.java
sabot/kernel/src/main/java/com/dremio/exec/store/iceberg/IcebergExecutionDatasetAccessor.java
sabot/kernel/src/main/java/com/dremio/exec/store/parquet/ParquetFormatDatasetAccessor.java
