Fix index name with uppercase letter issue

[dai-chen]

Description

OpenSearch has restriction on index name and only allows lowercase letter. Because Flint index is not registered to Glue/Hive metastore, table name and index name given in create statement is encoded into OpenSearch index name.

Without the fix

SQL statement such as CREATE SKIPPING INDEX ON myGlue.default.alb_logs will fail due to capital G and flint_myGlue_default_alb_logs_skipping_index index name generated.

With the fix

For any API, do this lowercase conversion in low-level FlintOpenSearchClient since this is restriction in OpenSearch store.

Documentation

Updated user manual with example and the limitation caused by this:

1. Naming convention: https://github.com/dai-chen/opensearch-spark/blob/fix-uppercase-index-name-issue/docs/index.md#opensearch
2. Limitation: https://github.com/dai-chen/opensearch-spark/blob/fix-uppercase-index-name-issue/docs/index.md#flint-index-naming

Refactoring

Potential refactor for FlintOpenSearchClient code in future:

  # Current
  @Override public void createIndex(String indexName, FlintMetadata metadata) {
    String osIndexName = toLowercase(indexName);
    try (RestHighLevelClient client = createClient()) {
        ...

  # Approach 1 by lambda
    return performAction(indexName, (client, osIndexName) -> ... );

  # Approach 2 by fluent API
    return withFlintIndex(indexName)
        .perform((client, osIndexName) -> ... );

  # Approach 3 by AOP
  class SomeClientWrapperForAop
      public void createIndex(String indexName, FlintMetadata metadata) {
          client.createIndex(toLowercase(indexName), metadata)
      ...

Issues Resolved

N/A

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