Performing any long running task or CPU intensive work on transport_worker threads is problematic. This is typically very bad for cluster stability.

This issue has been filed to examine the usage of transport_worked threads by ESQL, with the intention of "offloading" as much as possible, including deserialising large(ish) amounts of data.
x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/enrich/EnrichLookupService.java
public String getDescription() {
                    return lookupDescription(sessionId, shardId, matchType, matchField, extractFields, inputPage.getPositionCount());
                }
            };
        }
    }
    private static String lookupDescription(
        String sessionId,
        ShardId shardId,
        String matchType,
        String matchField,
        List<NamedExpression> extractFields,
        int positionCount
    ) {
        return "ENRICH_LOOKUP("
            + " session="
            + sessionId
            + " ,shard="
            + shardId
            + " ,match_type="
            + matchType
            + " ,match_field="
            + matchField
            + " ,extract_fields="
            + extractFields
            + " ,positions="
            + positionCount
            + ")";
    }
    private static class LookupResponse extends TransportResponse {