feat(exporter): unified Arrow exporter with GUC + end-to-end TAP test

include/config/guc.h

@@ -33,6 +33,7 @@ extern int psch_min_duration_us;
 extern int psch_normalize_cache_max;
 extern double psch_sample_rate;
 extern bool psch_otel_arrow_passthrough;
+extern bool psch_use_unified_arrow_exporter;
 extern int psch_otel_max_block_bytes;
 extern char* psch_extra_attributes;
 extern char* psch_debug_arrow_dump_dir;

src/config/guc.c

@@ -35,6 +35,7 @@ int psch_min_duration_us = 0;
 int psch_normalize_cache_max = 32768;
 double psch_sample_rate = 1.0;
 bool psch_otel_arrow_passthrough = false;
+bool psch_use_unified_arrow_exporter = false;
 int psch_otel_max_block_bytes = 3 * 1024 * 1024;  // 3 MiB (max: 16 MiB)
 char* psch_extra_attributes = NULL;
 char* psch_debug_arrow_dump_dir = NULL;
@@ -356,6 +357,23 @@ void PschInitGuc(void) {
       0,
       NULL, NULL, NULL);
 
+  DefineCustomBoolVariable(
+      "pg_stat_ch.use_unified_arrow_exporter",
+      "Use the StatsExporter-implementing Arrow exporter instead of arrow_batch.cc.",
+      "When enabled together with use_otel and otel_arrow_passthrough, the bgworker "
+      "builds Arrow IPC via the typed StatsExporter column interface, writing the "
+      "events_raw schema (typed integer ids, no sprintf decimal-string encoding). "
+      "When off, the legacy arrow_batch.cc path runs and produces the query_logs_arrow "
+      "wire shape. Default off; flip on to opt a producer into the new exporter. "
+      "PGC_POSTMASTER: the bgworker picks the exporter implementation at init time, "
+      "so a runtime change would mismatch the per-cycle dispatcher (Arrow batches "
+      "would silently drop, since OTelArrowExporter does not implement SendArrowBatch).",
+      &psch_use_unified_arrow_exporter,
+      false,
+      PGC_POSTMASTER,
+      0,
+      NULL, NULL, NULL);
+
   DefineCustomIntVariable(
       "pg_stat_ch.otel_max_block_bytes",
       "Maximum Arrow batch size in bytes per OTLP request.",