[core] Support bounded parallel builds for primary-key indexes

docs/docs/primary-key-table/global-index.mdx

@@ -104,7 +104,8 @@ Vector additionally requires:
 - `deletion-vectors.enabled = true`, except for `first-row`, where it must be `false`.
 - The configured ANN implementation on every writer and reader classpath.
 
-Exactly one vector column is currently supported per table.
+Multiple vector columns are supported. Each column owns an independent index with its own
+dimension, ANN implementation, distance metric, and build options.
 
 </TabItem>
 
@@ -265,11 +266,41 @@ schema validation.
 
 </details>
 
+### Index Multiple Vector Columns
+
+List the vector columns in `pk-vector.index.columns` and configure each column separately.
+For example, this Flink table indexes image and text embeddings independently:
+
+```sql
+CREATE TABLE multimodal_items (
+    id BIGINT,
+    image_embedding ARRAY<FLOAT> COMMENT '__VECTOR_FIELD;512',
+    text_embedding ARRAY<FLOAT> COMMENT '__VECTOR_FIELD;768',
+    PRIMARY KEY (id) NOT ENFORCED
+) WITH (
+    'bucket' = '8',
+    'deletion-vectors.enabled' = 'true',
+    'pk-vector.index.columns' = 'image_embedding,text_embedding',
+    'fields.image_embedding.pk-vector.index.type' = 'ivf-flat',
+    'fields.image_embedding.pk-vector.distance.metric' = 'cosine',
+    'fields.image_embedding.pk-vector.index.options' = '{"nlist":"256"}',
+    'fields.text_embedding.pk-vector.index.type' = 'ivf-flat',
+    'fields.text_embedding.pk-vector.distance.metric' = 'inner_product',
+    'fields.text_embedding.pk-vector.index.options' = '{"nlist":"512"}'
+);
+```
+
+Each vector search selects one column and uses that column's index, dimension, and distance
+metric. Listing multiple columns does not combine their vectors or define a fused ranking.
+Index coverage is tracked separately for each column, so an index on `image_embedding` does
+not cover a query on `text_embedding`.
+
 ### Options
 
 | Option | Default | Description |
 |---|---|---|
-| `pk-vector.index.columns` | Not set | Vector column to index. Exactly one vector column is currently supported. |
+| `pk-index.build.parallelism` | `1` | Maximum concurrent primary-key index build tasks per writer instance. Must be positive. |
+| `pk-vector.index.columns` | Not set | Comma-separated vector columns which own independent vector indexes. |
 | `fields.<column>.pk-vector.index.type` | Required | ANN implementation, such as `ivf-flat`, `ivf-pq`, `ivf-sq`, `ivf-rq`, or `diskann`. |
 | `fields.<column>.pk-vector.distance.metric` | `inner_product` | Distance metric: `l2`, `cosine`, or `inner_product`. |
 | `fields.<column>.pk-vector.index.options` | Not set | JSON object containing build options for the selected ANN implementation. |
@@ -300,6 +331,18 @@ in the [`paimon-full-text` README](https://github.com/apache/paimon/blob/master/
 
 ## Maintenance and Coverage
 
+Set `pk-index.build.parallelism` to `2`, for example, to allow two primary-key index build tasks
+to run concurrently within one writer instance. The default is `1`. Vector, Full Text, BTree,
+Bitmap, Multivalue, and FM indexes share this limit across that writer's columns and buckets.
+It is not the Flink or Spark job parallelism.
+
+Blocking commits start all configured indexes before waiting for their results. Non-blocking
+commits start builds and collect finished results without waiting; outstanding builds are
+collected by later commits. If an index fails during preparation, the coordinator rolls back
+that preparation, cancels outstanding builds, and cleans up uncommitted outputs. Previously
+committed snapshots remain valid. More concurrent builds can increase memory and I/O usage;
+each index implementation may also use its own internal threads.
+
 Paimon builds primary-key indexes from complete `COMPACT` data files above Level 0. An index group
 stores the source file names and row counts required to map index results back to physical rows.
 Data-file and index-file changes are committed in the same snapshot.
@@ -610,7 +653,7 @@ create a table with the desired definition and migrate the data.
 - Multivalue supports arrays of scalar element types accepted by the global-index key serializer.
   Null elements are not indexed. Higher array and element cardinality increases the expanded-sort
   I/O and index-file size.
-- Exactly one vector index column is currently supported per table.
+- Vector indexes are single-column indexes; each configured vector column has an independent index.
 - Exactly one full-text index column is currently supported per table.
 - Only `FLOAT` vectors are supported.
 - Indexes are built from eligible compact output, not directly from Level-0 appends.

docs/generated/core_configuration.html

@@ -1392,6 +1392,12 @@
             <td>String</td>
             <td>Comma-separated character columns indexed by primary-key full-text indexes. The first release supports exactly one column.</td>
         </tr>
+        <tr>
+            <td><h5>pk-index.build.parallelism</h5></td>
+            <td style="word-wrap: break-word;">1</td>
+            <td>Integer</td>
+            <td>The maximum number of concurrent primary-key index build tasks per writer instance, shared by its index columns and buckets. Must be greater than zero. Increasing this value may increase memory and I/O usage.</td>
+        </tr>
         <tr>
             <td><h5>pk-multivalue.index.columns</h5></td>
             <td style="word-wrap: break-word;">(none)</td>
@@ -1402,7 +1408,7 @@
             <td><h5>pk-vector.index.columns</h5></td>
             <td style="word-wrap: break-word;">(none)</td>
             <td>String</td>
-            <td>Comma-separated VECTOR columns indexed by primary-key vector indexes. Each column owns one index and must define fields.&lt;column&gt;.pk-vector.index.type. Index options and distance metric are also field-scoped. The first release supports exactly one column.</td>
+            <td>Comma-separated VECTOR columns indexed by primary-key vector indexes. Each column owns one index and must define fields.&lt;column&gt;.pk-vector.index.type. Index options and distance metric are also field-scoped.</td>
         </tr>
         <tr>
             <td><h5>postpone.batch-write-fixed-bucket</h5></td>

paimon-api/src/main/java/org/apache/paimon/CoreOptions.java

@@ -3163,6 +3163,16 @@ public String toString() {
                             "The batch size for lateral vector search. Each batch executes vector "
                                     + "topK search and table lookup for multiple query vectors.");
 
+    public static final ConfigOption<Integer> PK_INDEX_BUILD_PARALLELISM =
+            key("pk-index.build.parallelism")
+                    .intType()
+                    .defaultValue(1)
+                    .withDescription(
+                            "The maximum number of concurrent primary-key index build tasks per "
+                                    + "writer instance, shared by its index columns and buckets. "
+                                    + "Must be greater than zero. Increasing this value may increase "
+                                    + "memory and I/O usage.");
+
     public static final ConfigOption<String> PK_VECTOR_INDEX_COLUMNS =
             key("pk-vector.index.columns")
                     .stringType()
@@ -3171,8 +3181,7 @@ public String toString() {
                             "Comma-separated VECTOR columns indexed by primary-key vector indexes. "
                                     + "Each column owns one index and must define "
                                     + "fields.<column>.pk-vector.index.type. Index options and distance "
-                                    + "metric are also field-scoped. The first release supports exactly "
-                                    + "one column.");
+                                    + "metric are also field-scoped.");
 
     public static final ConfigOption<String> PK_BTREE_INDEX_COLUMNS =
             key("pk-btree.index.columns")
@@ -4991,6 +5000,16 @@ public boolean primaryKeyFMIndexEnabled() {
         return options.getOptional(PK_FM_INDEX_COLUMNS).isPresent();
     }
 
+    public int primaryKeyIndexBuildParallelism() {
+        int parallelism = options.get(PK_INDEX_BUILD_PARALLELISM);
+        checkArgument(
+                parallelism > 0,
+                "%s must be greater than zero, but is %s.",
+                PK_INDEX_BUILD_PARALLELISM.key(),
+                parallelism);
+        return parallelism;
+    }
+
     public List<String> primaryKeyVectorIndexColumns() {
         return primaryKeyIndexColumns(PK_VECTOR_INDEX_COLUMNS);
     }
@@ -5122,15 +5141,6 @@ private Options primaryKeySortedIndexOptions(
         return resolved;
     }
 
-    public String primaryKeyVectorIndexColumn() {
-        List<String> columns = primaryKeyVectorIndexColumns();
-        checkArgument(
-                columns.size() == 1,
-                "pk-vector.index.columns must contain exactly one column in the first release, but is %s.",
-                columns);
-        return columns.get(0);
-    }
-
     @Nullable
     public String primaryKeyVectorIndexType(String column) {
         return options.get("fields." + column + ".pk-vector.index.type");

paimon-common/src/test/java/org/apache/paimon/globalindex/testvector/TestVectorGlobalIndexerFactory.java

@@ -40,6 +40,11 @@ public String identifier() {
 
     @Override
     public GlobalIndexer create(List<DataField> indexFields, Options options) {
+        String metric = options.getString(IDENTIFIER + ".metric", null);
+        if (metric != null) {
+            options = new Options(options.toMap());
+            options.setString(TestVectorGlobalIndexer.OPT_METRIC, metric);
+        }
         if (indexFields.size() == 1) {
             return new TestVectorGlobalIndexer(indexFields.get(0).type(), options);
         }