MDEV-17096 Pushdown of simple derived tables to storage engines

MDEV-17631 select_handler for a full query pushdown

Interfaces + Proof of Concept for federatedx with test cases.

The interfaces have been developed for integration of ColumnStore engine.

1 files changed, 145 insertions, 0 deletions

diff --git a/sql/select_handler.cc b/sql/select_handler.cc
new file mode 100644
index 00000000000..17475f4907d
--- /dev/null
+++ b/sql/select_handler.cc
@@ -0,0 +1,145 @@
+#include "mariadb.h"
+#include "sql_priv.h"
+#include "sql_select.h"
+#include "select_handler.h"
+
+
+Pushdown_select::Pushdown_select(SELECT_LEX *sel, select_handler *h)
+  : select(sel), handler(h)
+{ 
+  is_analyze= handler->thd->lex->analyze_stmt;
+}
+
+Pushdown_select::~Pushdown_select()
+{
+  delete handler;
+  select->select_h= NULL;
+}
+
+bool Pushdown_select::init()
+{
+  List<Item> types;
+  TMP_TABLE_PARAM tmp_table_param;
+  THD *thd= handler->thd;
+  DBUG_ENTER("Pushdown_select::init");
+  if (select->master_unit()->join_union_item_types(thd, types, 1))
+    DBUG_RETURN(true);
+  tmp_table_param.init();
+  tmp_table_param.field_count= types.elements;
+
+  handler->table= create_tmp_table(thd, &tmp_table_param, types,
+                                   (ORDER *) 0, false, 0,
+                                   TMP_TABLE_ALL_COLUMNS, 1,
+                                   &empty_clex_str, true, false);
+  if (!handler->table)
+    DBUG_RETURN(true);
+  if (handler->table->fill_item_list(&result_columns))
+    DBUG_RETURN(true);
+  DBUG_RETURN(false);  
+}
+
+bool Pushdown_select::send_result_set_metadata()
+{
+  THD *thd= handler->thd;
+  Protocol *protocol= thd->protocol;
+  DBUG_ENTER("Pushdown_select::send_result_set_metadata");
+
+#ifdef WITH_WSREP
+  if (WSREP(thd) && thd->wsrep_retry_query)
+  {
+    WSREP_DEBUG("skipping select metadata");
+    DBUG_RETURN(false);
+  }
+  #endif /* WITH_WSREP */
+  if (protocol->send_result_set_metadata(&result_columns,
+                                         Protocol::SEND_NUM_ROWS |
+                                         Protocol::SEND_EOF))
+    DBUG_RETURN(true);
+
+  DBUG_RETURN(false);
+}
+
+bool Pushdown_select::send_data()
+{
+  THD *thd= handler->thd;
+  Protocol *protocol= thd->protocol;
+  DBUG_ENTER("Pushdown_select::send_data");
+
+  if (thd->killed == ABORT_QUERY)
+    DBUG_RETURN(false);
+
+  protocol->prepare_for_resend();
+  if (protocol->send_result_set_row(&result_columns))
+  {
+    protocol->remove_last_row();
+    DBUG_RETURN(true);
+  }
+ 
+  thd->inc_sent_row_count(1);
+
+  if (thd->vio_ok())
+    DBUG_RETURN(protocol->write());
+
+  DBUG_RETURN(false);
+}
+
+bool Pushdown_select::send_eof()
+{
+  THD *thd= handler->thd;
+  DBUG_ENTER("Pushdown_select::send_eof");
+
+  /* 
+    Don't send EOF if we're in error condition (which implies we've already
+    sent or are sending an error)
+  */
+  if (thd->is_error())
+    DBUG_RETURN(true);
+  ::my_eof(thd);  
+  DBUG_RETURN(false);
+}
+
+int Pushdown_select::execute()
+{
+  int err;
+  THD *thd= handler->thd;
+
+  DBUG_ENTER("Pushdown_select::execute");
+
+  if ((err= handler->init_scan()))
+    goto error;
+
+  if (is_analyze)
+  {
+    handler->end_scan();
+    DBUG_RETURN(0);
+  }
+  
+  if (send_result_set_metadata())
+    DBUG_RETURN(-1);
+  
+  while (!(err= handler->next_row()))
+  {
+    if (thd->check_killed() || send_data())
+    {
+      handler->end_scan();
+      DBUG_RETURN(-1);
+    }
+  }
+
+  if (err != 0 && err != HA_ERR_END_OF_FILE)
+    goto error;
+
+  if ((err= handler->end_scan()))
+   goto error_2;
+
+  if (send_eof())
+    DBUG_RETURN(-1);
+
+  DBUG_RETURN(0);
+
+error:
+  handler->end_scan();
+error_2:
+  handler->print_error(err, MYF(0));
+  DBUG_RETURN(-1);                              // Error not sent to client
+}