feat(trace/api): Add support for projecting tables

This change adds support for projecting certain columns of a table. This
enables faster reading for tables with high number of columns.
Currently, we support projection in the Parquet-based workload formats.
Other formats are text-based and will probably not benefit much from
projection.

3 files changed, 10 insertions, 4 deletions

diff --git a/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/Table.kt b/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/Table.kt
index b0181cbc..05d0234a 100644
--- a/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/Table.kt
+++ b/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/Table.kt
@@ -42,9 +42,11 @@ public interface Table {
     public val partitionKeys: List<TableColumn<*>>
 
     /**
-     * Open a [TableReader] for this table.
+     * Open a [TableReader] for a projection of this table.
+     *
+     * @param projection The list of columns to fetch from the table or `null` if no projection is performed.
      */
-    public fun newReader(): TableReader
+    public fun newReader(projection: List<TableColumn<*>>? = null): TableReader
 
     /**
      * Open a [TableWriter] for this table.
diff --git a/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/internal/TableImpl.kt b/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/internal/TableImpl.kt
index 24551edb..b848e19a 100644
--- a/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/internal/TableImpl.kt
+++ b/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/internal/TableImpl.kt
@@ -43,7 +43,9 @@ internal class TableImpl(val trace: TraceImpl, override val name: String) : Tabl
     override val partitionKeys: List<TableColumn<*>>
         get() = details.partitionKeys
 
-    override fun newReader(): TableReader = trace.format.newReader(trace.path, name)
+    override fun newReader(projection: List<TableColumn<*>>?): TableReader {
+        return trace.format.newReader(trace.path, name, projection)
+    }
 
     override fun newWriter(): TableWriter = trace.format.newWriter(trace.path, name)
 
diff --git a/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/spi/TraceFormat.kt b/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/spi/TraceFormat.kt
index f2e610db..47761e0f 100644
--- a/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/spi/TraceFormat.kt
+++ b/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/spi/TraceFormat.kt
@@ -22,6 +22,7 @@
 
 package org.opendc.trace.spi
 
+import org.opendc.trace.TableColumn
 import org.opendc.trace.TableReader
 import org.opendc.trace.TableWriter
 import java.nio.file.Path
@@ -68,10 +69,11 @@ public interface TraceFormat {
      *
      * @param path The path to the trace to open.
      * @param table The name of the table to open a [TableReader] for.
+     * @param projection The list of [TableColumn]s to project or `null` if no projection is performed.
      * @throws IllegalArgumentException If [table] does not exist.
      * @return A [TableReader] instance for the table.
      */
-    public fun newReader(path: Path, table: String): TableReader
+    public fun newReader(path: Path, table: String, projection: List<TableColumn<*>>?): TableReader
 
     /**
      * Open a [TableWriter] for the specified [table].