MDEV-8235: Expose check_slave_start_position as SQL function GTID_CHECK_POS()

mysql-test/main/gtid_check_pos.result

@@ -0,0 +1,37 @@
+#
+# MDEV-8235 Expose check_slave_start_position as SQL function
+#
+# 1. Set up some basic GTID history
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1);
+INSERT INTO t1 VALUES (2);
+# Get the current GTID position manually and verify it exists
+SELECT GTID_CHECK_POS('GTID_POS');
+GTID_CHECK_POS('GTID_POS')
+1
+# 2. Verify invalid inputs
+SELECT GTID_CHECK_POS('invalid-format');
+ERROR HY000: Could not parse GTID list
+SELECT GTID_CHECK_POS(NULL);
+GTID_CHECK_POS(NULL)
+NULL
+# 3. Check for a very old purged GTID
+# (Simulate purging all logs)
+FLUSH LOGS;
+PURGE BINARY LOGS BEFORE NOW();
+# Depending on when it is executed, '0-1-1' might still be
+# reachable if we haven't actually purged the very first file
+# but purge binary logs before now() should remove everything 
+# except the active one.
+# Since we want a deterministic test, let's check
+# a completely fake server_id / seq_no that shouldn't exist
+SELECT GTID_CHECK_POS('0-99-9999999');
+GTID_CHECK_POS('0-99-9999999')
+1
+# 4. Check for an otherwise valid GTID (right domain and server)
+# that is absent (sequence number is in the future).
+SELECT GTID_CHECK_POS('ABSENT_GTID');
+GTID_CHECK_POS('ABSENT_GTID')
+1
+# Cleanup
+DROP TABLE t1;

mysql-test/main/gtid_check_pos.test

@@ -0,0 +1,44 @@
+--source include/have_log_bin.inc
+
+--echo #
+--echo # MDEV-8235 Expose check_slave_start_position as SQL function
+--echo #
+
+--echo # 1. Set up some basic GTID history
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1);
+INSERT INTO t1 VALUES (2);
+
+--echo # Get the current GTID position manually and verify it exists
+let $pos= `SELECT @@GLOBAL.gtid_binlog_pos`;
+--replace_result $pos GTID_POS
+eval SELECT GTID_CHECK_POS('$pos');
+
+--echo # 2. Verify invalid inputs
+--error ER_INCORRECT_GTID_STATE
+SELECT GTID_CHECK_POS('invalid-format');
+SELECT GTID_CHECK_POS(NULL);
+
+--echo # 3. Check for a very old purged GTID
+--echo # (Simulate purging all logs)
+FLUSH LOGS;
+PURGE BINARY LOGS BEFORE NOW();
+
+--echo # Depending on when it is executed, '0-1-1' might still be
+--echo # reachable if we haven't actually purged the very first file
+--echo # but purge binary logs before now() should remove everything 
+--echo # except the active one.
+
+--echo # Since we want a deterministic test, let's check
+--echo # a completely fake server_id / seq_no that shouldn't exist
+SELECT GTID_CHECK_POS('0-99-9999999');
+
+--echo # 4. Check for an otherwise valid GTID (right domain and server)
+--echo # that is absent (sequence number is in the future).
+let $server_id= `SELECT @@GLOBAL.server_id`;
+let $absent_gtid= 0-$server_id-99999999;
+--replace_result $absent_gtid ABSENT_GTID
+eval SELECT GTID_CHECK_POS('$absent_gtid');
+
+--echo # Cleanup
+DROP TABLE t1;

sql/item_cmpfunc.h

@@ -2920,6 +2920,29 @@ class Item_func_null_predicate :public Item_bool_func
 };
 
 
+class Item_func_gtid_check_pos :public Item_bool_func
+{
+  String tmp_value;
+public:
+  Item_func_gtid_check_pos(THD *thd, Item *a): Item_bool_func(thd, a) {}
+  LEX_CSTRING func_name_cstring() const override
+  {
+    static LEX_CSTRING name= {STRING_WITH_LEN("gtid_check_pos") };
+    return name;
+  }
+  bool val_bool() override;
+  bool fix_length_and_dec(THD *thd) override
+  {
+    set_maybe_null();
+    return FALSE;
+  }
+
+protected:
+  Item *shallow_copy(THD *thd) const override
+  { return get_item_copy<Item_func_gtid_check_pos>(thd, this); }
+};
+
+
 class Item_func_isnull :public Item_func_null_predicate
 {
 public:

sql/item_create.cc

@@ -528,6 +528,19 @@ class Create_func_connection_id : public Create_func_arg0
 };
 
 
+class Create_func_gtid_check_pos : public Create_func_arg1
+{
+public:
+  Item *create_1_arg(THD *thd, Item *arg1) override;
+
+  static Create_func_gtid_check_pos s_singleton;
+
+protected:
+  Create_func_gtid_check_pos() = default;
+  ~Create_func_gtid_check_pos() override = default;
+};
+
+
 class Create_func_database : public Create_func_arg0
 {
 public:
@@ -3576,6 +3589,15 @@ Create_func_connection_id::create_builder(THD *thd)
 }
 
 
+Create_func_gtid_check_pos Create_func_gtid_check_pos::s_singleton;
+
+Item*
+Create_func_gtid_check_pos::create_1_arg(THD *thd, Item *arg1)
+{
+  return new (thd->mem_root) Item_func_gtid_check_pos(thd, arg1);
+}
+
+
 Create_func_database Create_func_database::s_singleton;
 
 Item*
@@ -6355,6 +6377,7 @@ const Native_func_registry func_array[] =
   { { STRING_WITH_LEN("CONCAT_OPERATOR_ORACLE") }, BUILDER(Create_func_concat_operator_oracle)},
   { { STRING_WITH_LEN("CONCAT_WS") }, BUILDER(Create_func_concat_ws)},
   { { STRING_WITH_LEN("CONNECTION_ID") }, BUILDER(Create_func_connection_id)},
+  { { STRING_WITH_LEN("GTID_CHECK_POS") }, BUILDER(Create_func_gtid_check_pos)},
   { { STRING_WITH_LEN("CONV") }, BUILDER(Create_func_conv)},
   { { STRING_WITH_LEN("CONVERT_TZ") }, BUILDER(Create_func_convert_tz)},
   { { STRING_WITH_LEN("COS") }, BUILDER(Create_func_cos)},

sql/item_func.cc

@@ -37,6 +37,7 @@
 #include "sql_acl.h"                            // EXECUTE_ACL
 #include "mysqld.h"                             // LOCK_short_uuid_generator
 #include "rpl_mi.h"
+
 #include "sql_time.h"
 #include <m_ctype.h>
 #include <hash.h>
@@ -51,6 +52,7 @@
 #include "debug_sync.h"
 #include "sql_base.h"
 #include "sql_cte.h"
+#include "sql_repl.h"
 #ifdef WITH_WSREP
 #include "mysql/service_wsrep.h"
 #endif /* WITH_WSREP */
@@ -824,6 +826,31 @@ String *Item_int_func::val_str(String *str)
 }
 
 
+bool Item_func_gtid_check_pos::val_bool()
+{
+  DBUG_ASSERT(fixed());
+  String *gtid_str= args[0]->val_str(&tmp_value);
+  if ((null_value= args[0]->null_value))
+    return 0;
+
+#ifndef HAVE_REPLICATION
+  (void)gtid_str;
+  my_error(ER_NOT_SUPPORTED_YET, MYF(0), "GTID_CHECK_POS");
+  null_value= 1;
+  return 0;
+#else
+  bool is_reachable= false;
+  if (rpl_gtid_pos_check_reachable(gtid_str, &is_reachable))
+  {
+    null_value= 1;
+    return 0;
+  }
+  null_value= 0;
+  return is_reachable;
+#endif
+}
+
+
 bool Item_func_connection_id::fix_length_and_dec(THD *thd)
 {
   if (Item_long_func::fix_length_and_dec(thd))

sql/item_func.h

@@ -1505,6 +1505,9 @@ class Item_func_connection_id :public Item_long_func
 };
 
 
+
+
+
 class Item_func_signed :public Item_int_func
 {
 public:

sql/sql_repl.cc

@@ -32,6 +32,7 @@
 #include "semisync_slave.h"
 #include "mysys_err.h"
 #include "gtid_index.h"
+#include "item_cmpfunc.h"
 
 
 enum enum_gtid_until_state {
@@ -5838,4 +5839,60 @@ int compare_log_name(const char *log_1, const char *log_2) {
   return res;
 }
 
+bool rpl_gtid_pos_check_reachable(String *gtid_str, bool *is_reachable)
+{
+
+  slave_connection_state state;
+  char buf[FN_REFLEN] = {0};
+  const char *errormsg;
+
+  if (!mysql_bin_log.is_open())
+  {
+    my_error(ER_NO_BINARY_LOGGING, MYF(0));
+    return true;
+  }
+
+  if (state.load(gtid_str->ptr(), gtid_str->length()))
+  {
+    /* 
+      We purposefully do not swallow the error here. If the user passes an 
+      ill-formed string, state.load throws ER_INCORRECT_GTID_STATE which 
+      will correctly abort the statement and notify the user.
+    */
+    return true;
+  }
+
+  /*
+    gtid_find_binlog_pos will natively iterate over the entire `state` hash,
+    evaluating every GTID provided in the comma-separated list.
+
+    If ANY of the requested GTIDs are found to be purged from the binary logs, 
+    it returns a non-null error message pinpointing the purged GTID.
+
+    If ALL GTIDs within the requested state natively resolve (meaning they exist
+    in our index/binlogs, or are safely in the future), it returns a null errormsg.
+
+    We disregard `found_in_index` and `out_start_seek` counts since we are only doing 
+    boolean viability checking of the provided GTIDs, not actually initializing a dump thread.
+  */
+  bool found_in_index= false;
+  uint32 out_start_seek= 0;
+  rpl_binlog_state until_binlog_state;
+  until_binlog_state.init();
+  slave_connection_state until_gtid_state;
+
+  errormsg= gtid_find_binlog_pos(&state, buf, &until_gtid_state, &until_binlog_state, &found_in_index, &out_start_seek);
+
+  until_binlog_state.free();
+
+  if (errormsg)
+  {
+    *is_reachable= false;
+    return false; // At least one requested GTID has been purged.
+  }
+
+  *is_reachable= true;
+  return false; // All requested GTIDs are currently viable/reachable.
+}
+
 #endif /* HAVE_REPLICATION */

sql/sql_repl.h

@@ -72,6 +72,8 @@ int rpl_append_gtid_state(String *dest, bool use_binlog);
 int rpl_load_gtid_state(slave_connection_state *state, bool use_binlog);
 bool rpl_gtid_pos_check(THD *thd, char *str, size_t len);
 bool rpl_gtid_pos_update(THD *thd, char *str, size_t len);
+bool rpl_gtid_pos_check_reachable(String *gtid_str, bool *is_reachable);
+
 #else
 
 struct LOAD_FILE_IO_CACHE : public IO_CACHE { };