今天简单说明了下关于InformationSchemaCatalog 服务的介绍，当时介绍的InformationSchemaCatalog 更多属于基础能力（实际上这个类核心还是dremio 内部使用的）
对于在bi 工具以及系统使用的，dremio 是通过了独立的存储扩展（dremio 存储扩展比较方便，我们可以灵活的扩展dremio）
InfoSchemaConf定义
@SourceType(value = "INFORMATION_SCHEMA", configurable = false)
public class InfoSchemaConf extends ConnectionConf<InfoSchemaConf, InfoSchemaStoragePlugin> {
@Override
public InfoSchemaStoragePlugin newPlugin(SabotContext context, String name, Provider<StoragePluginId> pluginIdProvider) {// InfoSchemaStoragePlugin 存储扩展，实现了对于数据的查询,name 以及明确了查询了格式必须是INFORMATION_SCHEMA了，就类似我们自己开发的plugin 配置的sourcename
return new InfoSchemaStoragePlugin(context, name);
}
@Override
public boolean isInternal() {return true;
}
}
InfoSchemaStoragePlugin 处理
InfoSchemaStoragePlugin 核心是读取操作，因为实际的数据已经直接在不通catalog 处理了（catalog 依赖了InformationSchemaCatalog服务）
类图
核心部分，主要包含了datasethandler 的处理
@Override
public DatasetHandleListing listDatasetHandles(GetDatasetOption... options) {return () -> Arrays.stream(InformationSchemaTable.values()).iterator();
}
@Override
public Optional<DatasetHandle> getDatasetHandle(EntityPath datasetPath, GetDatasetOption... options) {if (datasetPath.size() != 2) {return Optional.empty();
}
final InformationSchemaTable table = TABLE_MAP.get(datasetPath.getName().toLowerCase());
if (table == null) {return Optional.empty();
}
return Optional.of(table);
}
对于datasethandle 的处理，nformationSchema包装了自己了，使用了枚举类型（InformationSchemaTable 类）
对于数据的读取操作，使用了InformationSchemaRecordReader， 此方法内部使用了包装的rpc 服务（InformationSchemaServiceGrpc）
具体在catalog-api 这个服务中
代码
public class InformationSchemaRecordReader extends AbstractRecordReader {private static final org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(InformationSchemaRecordReader.class);
// grpc 的InformationSchemaServiceBlockingStub
private final InformationSchemaServiceBlockingStub catalogStub;
// 使用了InformationSchemaTable
private final InformationSchemaTable table;
private final String catalogName;
private final String username;
private final SearchQuery searchQuery;
private final boolean complexTypeSupport;
private Context.CancellableContext context;
private TableWriter<?> tableWriter;
public InformationSchemaRecordReader(
OperatorContext context,
List<SchemaPath> fields,
InformationSchemaServiceBlockingStub catalogStub,
InformationSchemaTable table,
String catalogName,
String username,
SearchQuery searchQuery,
boolean complexTypeSupport
) {super(context, fields);
this.catalogStub = catalogStub;
this.table = table;
this.catalogName = catalogName;
this.username = username;
this.searchQuery = searchQuery;
this.complexTypeSupport = complexTypeSupport;
}
@Override
public void setup(OutputMutator output) {context = Context.current().withCancellation();
context.run(() -> {tableWriter = createTableWriter();
tableWriter.init(output);
});
}
@Override
public int next() {Preconditions.checkNotNull(tableWriter, "Reader must be #setup first");
return tableWriter.write(numRowsPerBatch);
}
@Override
public void close() throws Exception {if (context != null) {context.close();
}
context = null;
tableWriter = null;
}
@Override
protected boolean supportsSkipAllQuery() {return true;
}
private Set<String> getGivenFields() {return getColumns()
stream()
peek(path -> Preconditions.checkArgument(path.isSimplePath()))
map(path -> path.getAsUnescapedPath().toUpperCase())
collect(Collectors.toSet());
}
private TableWriter<?> createTableWriter() {final Set<String> selectedFields =
isStarQuery() ? InformationSchemaMetadata.getAllFieldNames(table.getRecordSchema()) : getGivenFields();
switch (table) {
case CATALOGS: {final ListCatalogsRequest.Builder catalogsRequest = ListCatalogsRequest.newBuilder()
setUsername(username);
if (searchQuery != null) {catalogsRequest.setQuery(searchQuery);
}
// start Catalog stream from catalog service
return new CatalogsTableWriter(catalogStub.listCatalogs(catalogsRequest.build()), selectedFields, catalogName);
}
case SCHEMATA: {final ListSchemataRequest.Builder schemataRequest = ListSchemataRequest.newBuilder()
setUsername(username);
if (searchQuery != null) {schemataRequest.setQuery(searchQuery);
}
// start Schema stream from catalog service
return new SchemataTableWriter(catalogStub.listSchemata(schemataRequest.build()), selectedFields, catalogName);
}
case TABLES: {final ListTablesRequest.Builder tablesRequest = ListTablesRequest.newBuilder()
setUsername(username);
if (searchQuery != null) {tablesRequest.setQuery(searchQuery);
}
// start Table stream from catalog service
return new TablesTableWriter(catalogStub.listTables(tablesRequest.build()), selectedFields, catalogName);
}
case VIEWS: {final ListViewsRequest.Builder viewsRequest = ListViewsRequest.newBuilder()
setUsername(username);
if (searchQuery != null) {viewsRequest.setQuery(searchQuery);
}
// start View stream from catalog service
return new ViewsTableWriter(catalogStub.listViews(viewsRequest.build()), selectedFields, catalogName);
}
case COLUMNS: {final ListTableSchemataRequest.Builder columnsRequest = ListTableSchemataRequest.newBuilder()
setUsername(username);
if (searchQuery != null) {columnsRequest.setQuery(searchQuery);
}
// start TableSchema stream from catalog service
final Iterator<TableSchema> tableSchemata = catalogStub.listTableSchemata(columnsRequest.build());
// For each TableSchema, iterates over #flatMap of batch_schema field, which represents the records in the
// "COLUMNS" table, and not the TableSchema message itself (unlike other tables).
final Iterator<Column> columnIterator = new AbstractIterator<Column>() {Iterator<Column> currentIterator = null;
@Override
protected Column computeNext() {while (true) {if (currentIterator != null && currentIterator.hasNext()) {return currentIterator.next();
}
if (!tableSchemata.hasNext()) {return endOfData();
}
// Gets next TableSchema from the catalog service only after exhausting the current one. See comment in
// TableWriter#write.
final TableSchema currentSchema = tableSchemata.next();
BatchSchema bs = BatchSchema.deserialize(currentSchema.getBatchSchema().toByteArray());
//If an inconsistency is detected don't attempt converting to Arrow format since it will cause an assertion failure. Put out a warning and move on to next row.
if (bs.getFieldCount() == 0) {// Add a warning message to indicate this table has missing fields
logger.warn("{}.{}.{} has missing fields or incorrect format. ", currentSchema.getCatalogName(), currentSchema.getSchemaName(), currentSchema.getTableName());continue;
}
final RelDataType rowType =
CalciteArrowHelper.wrap(bs)
toCalciteRecordType(JavaTypeFactoryImpl.INSTANCE, complexTypeSupport);
//noinspection ConstantConditions
currentIterator = Iterators.transform(rowType.getFieldList().iterator(),
field -> new Column(Strings.isNullOrEmpty(catalogName) ? currentSchema.getCatalogName() : catalogName,
currentSchema.getSchemaName(),
currentSchema.getTableName(),
field));
}
}
};
return new ColumnsTableWriter(columnIterator, selectedFields, catalogName);
}
default:
throw UserException.unsupportedError()
message("InformationSchemaRecordReader does not support table of '%s' type", table)buildSilently();
}
}
}
此调用链的学习，可以参考我以前写的文章
参考调用链
说明
如果了解presto 以及trion 这类查询引擎的话，他们的InformationSchema 是到插件级别的，并不是类似dremio以及drill 这种工具的，全局级别的
参考资料
sabot/kernel/src/main/java/com/dremio/exec/store/ischema/InfoSchemaConf.java
sabot/kernel/src/main/java/com/dremio/exec/store/ischema/InformationSchemaTable.java
sabot/kernel/src/main/java/com/dremio/exec/store/ischema/InfoSchemaStoragePlugin.java
sabot/kernel/src/main/java/com/dremio/exec/store/ischema/InformationSchemaRecordReader.java
services/catalog-api/target/generated-sources/protobuf/com/dremio/service/catalog/InformationSchemaServiceGrpc.java
