~drizzle-trunk/drizzle/development

/* -*- mode: c++; c-basic-offset: 2; indent-tabs-mode: nil; -*-

 *  vim:expandtab:shiftwidth=2:tabstop=2:smarttab:

 *

 *  Copyright (C) 2008 Sun Microsystems

 *

 *  This program is free software; you can redistribute it and/or modify

 *  it under the terms of the GNU General Public License as published by

 *  the Free Software Foundation; version 2 of the License.

 *

 *  This program is distributed in the hope that it will be useful,

 *  but WITHOUT ANY WARRANTY; without even the implied warranty of

 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 *  GNU General Public License for more details.

 *

 *  You should have received a copy of the GNU General Public License

 *  along with this program; if not, write to the Free Software

 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

 */

#ifndef DRIZZLED_SESSION_H

#define DRIZZLED_SESSION_H

/* Classes in mysql */

#include <drizzled/protocol.h>

#include <drizzled/sql_locale.h>

#include <drizzled/ha_trx_info.h>

#include <mysys/my_tree.h>

#include <drizzled/handler.h>

#include <drizzled/current_session.h>

#include <drizzled/sql_error.h>

#include <drizzled/query_arena.h>

#include <drizzled/file_exchange.h>

#include <drizzled/select_result_interceptor.h>

#include <drizzled/authentication.h>

#include <drizzled/db.h>

#include <drizzled/xid.h>

#include <netdb.h>

#include <string>

#include <bitset>

#define MIN_HANDSHAKE_SIZE      6

class Lex_input_stream;

class user_var_entry;

class Copy_field;

class Table_ident;

extern char internal_table_name[2];

extern char empty_c_string[1];

extern const char **errmesg;

#define TC_HEURISTIC_RECOVER_COMMIT   1

#define TC_HEURISTIC_RECOVER_ROLLBACK 2

extern uint32_t tc_heuristic_recover;

/*

  The COPY_INFO structure is used by INSERT/REPLACE code.

  The schema of the row counting by the INSERT/INSERT ... ON DUPLICATE KEY

  UPDATE code:

    If a row is inserted then the copied variable is incremented.

    If a row is updated by the INSERT ... ON DUPLICATE KEY UPDATE and the

      new data differs from the old one then the copied and the updated

      variables are incremented.

    The touched variable is incremented if a row was touched by the update part

      of the INSERT ... ON DUPLICATE KEY UPDATE no matter whether the row

      was actually changed or not.

*/

typedef struct st_copy_info {

  ha_rows records; /**< Number of processed records */

  ha_rows deleted; /**< Number of deleted records */

  ha_rows updated; /**< Number of updated records */

  ha_rows copied;  /**< Number of copied records */

  ha_rows error_count;

  ha_rows touched; /* Number of touched records */

  enum enum_duplicates handle_duplicates;

  int escape_char, last_errno;

  bool ignore;

  /* for INSERT ... UPDATE */

  List<Item> *update_fields;

  List<Item> *update_values;

  /* for VIEW ... WITH CHECK OPTION */

} COPY_INFO;

typedef struct drizzled_lock_st

{

  Table **table;

  uint32_t table_count,lock_count;

  THR_LOCK_DATA **locks;

} DRIZZLE_LOCK;

#include <drizzled/lex_column.h>

class select_result;

class Time_zone;

#define Session_SENTRY_MAGIC 0xfeedd1ff

#define Session_SENTRY_GONE  0xdeadbeef

#define Session_CHECK_SENTRY(session) assert(session->dbug_sentry == Session_SENTRY_MAGIC)

struct system_variables

{

  system_variables() {};

  /*

    How dynamically allocated system variables are handled:

    The global_system_variables and max_system_variables are "authoritative"

    They both should have the same 'version' and 'size'.

    When attempting to access a dynamic variable, if the session version

    is out of date, then the session version is updated and realloced if

    neccessary and bytes copied from global to make up for missing data.

  */

  ulong dynamic_variables_version;

  char* dynamic_variables_ptr;

  uint32_t dynamic_variables_head;  /* largest valid variable offset */

  uint32_t dynamic_variables_size;  /* how many bytes are in use */

  uint64_t myisam_max_extra_sort_file_size;

  uint64_t max_heap_table_size;

  uint64_t tmp_table_size;

  ha_rows select_limit;

  ha_rows max_join_size;

  uint64_t auto_increment_increment;

  uint64_t auto_increment_offset;

  uint64_t bulk_insert_buff_size;

  uint64_t join_buff_size;

  uint32_t max_allowed_packet;

  uint64_t max_error_count;

  uint64_t max_length_for_sort_data;

  size_t max_sort_length;

  uint64_t max_tmp_tables;

  uint64_t min_examined_row_limit;

  uint32_t myisam_stats_method;

  uint32_t net_buffer_length;

  uint32_t net_read_timeout;

  uint32_t net_retry_count;

  uint32_t net_wait_timeout;

  uint32_t net_write_timeout;

  bool optimizer_prune_level;

  uint32_t optimizer_search_depth;

  /*

    Controls use of Engine-MRR:

      0 - auto, based on cost

      1 - force MRR when the storage engine is capable of doing it

      2 - disable MRR.

  */

  uint32_t optimizer_use_mrr;

  /* A bitmap for switching optimizations on/off */

  uint32_t optimizer_switch;

  uint64_t preload_buff_size;

  uint32_t read_buff_size;

  uint32_t read_rnd_buff_size;

  uint32_t div_precincrement;

  size_t sortbuff_size;

  uint32_t thread_handling;

  uint32_t tx_isolation;

  uint32_t completion_type;

  /* Determines which non-standard SQL behaviour should be enabled */

  uint32_t sql_mode;

  uint64_t max_seeks_for_key;

  size_t range_alloc_block_size;

  uint32_t query_alloc_block_size;

  uint32_t query_prealloc_size;

  uint32_t trans_alloc_block_size;

  uint32_t trans_prealloc_size;

  bool log_warnings;

  uint64_t group_concat_max_len;

  /* TODO: change this to my_thread_id - but have to fix set_var first */

  uint64_t pseudo_thread_id;

  bool low_priority_updates;

  bool new_mode;

  /*

    compatibility option:

      - index usage hints (USE INDEX without a FOR clause) behave as in 5.0

  */

  bool old_mode;

  bool engine_condition_pushdown;

  bool keep_files_on_create;

  bool old_alter_table;

  StorageEngine *storage_engine;

  /* Only charset part of these variables is sensible */

  const CHARSET_INFO  *character_set_filesystem;

  /* Both charset and collation parts of these variables are important */

  const CHARSET_INFO	*collation_server;

  const CHARSET_INFO	*collation_database;

  inline const CHARSET_INFO  *getCollation(void) 

  {

    return collation_database ? collation_database : collation_server;

  }

  /* Locale Support */

  MY_LOCALE *lc_time_names;

  Time_zone *time_zone;

};

extern struct system_variables global_system_variables;

#include "sql_lex.h"  /* only for SQLCOM_END */

/* per thread status variables */

typedef struct system_status_var

{

  uint64_t bytes_received;

  uint64_t bytes_sent;

  ulong com_other;

  ulong com_stat[(uint32_t) SQLCOM_END];

  ulong created_tmp_disk_tables;

  ulong created_tmp_tables;

  ulong ha_commit_count;

  ulong ha_delete_count;

  ulong ha_read_first_count;

  ulong ha_read_last_count;

  ulong ha_read_key_count;

  ulong ha_read_next_count;

  ulong ha_read_prev_count;

  ulong ha_read_rnd_count;

  ulong ha_read_rnd_next_count;

  ulong ha_rollback_count;

  ulong ha_update_count;

  ulong ha_write_count;

  ulong ha_prepare_count;

  ulong ha_savepoint_count;

  ulong ha_savepoint_rollback_count;

  /* KEY_CACHE parts. These are copies of the original */

  ulong key_blocks_changed;

  ulong key_blocks_used;

  ulong key_cache_r_requests;

  ulong key_cache_read;

  ulong key_cache_w_requests;

  ulong key_cache_write;

  /* END OF KEY_CACHE parts */

  ulong net_big_packet_count;

  ulong opened_tables;

  ulong opened_shares;

  ulong select_full_join_count;

  ulong select_full_range_join_count;

  ulong select_range_count;

  ulong select_range_check_count;

  ulong select_scan_count;

  ulong long_query_count;

  ulong filesort_merge_passes;

  ulong filesort_range_count;

  ulong filesort_rows;

  ulong filesort_scan_count;

  /*

    Number of statements sent from the client

  */

  ulong questions;

  /*

    IMPORTANT!

    SEE last_system_status_var DEFINITION BELOW.

    Below 'last_system_status_var' are all variables which doesn't make any

    sense to add to the /global/ status variable counter.

  */

  double last_query_cost;

} STATUS_VAR;

/*

  This is used for 'SHOW STATUS'. It must be updated to the last ulong

  variable in system_status_var which is makes sens to add to the global

  counter

*/

#define last_system_status_var questions

void mark_transaction_to_rollback(Session *session, bool all);

/**

  @class Statement

  @brief State of a single command executed against this connection.

  One connection can contain a lot of simultaneously running statements,

  some of which could be:

   - prepared, that is, contain placeholders,

  To perform some action with statement we reset Session part to the state  of

  that statement, do the action, and then save back modified state from Session

  to the statement. It will be changed in near future, and Statement will

  be used explicitly.

*/

class Statement: public ilink, public Query_arena

{

  Statement(const Statement &rhs);              /* not implemented: */

  Statement &operator=(const Statement &rhs);   /* non-copyable */

public:

  /*

    Uniquely identifies each statement object in thread scope; change during

    statement lifetime. FIXME: must be const

  */

   ulong id;

  /*

    MARK_COLUMNS_NONE:  Means mark_used_colums is not set and no indicator to

                        handler of fields used is set

    MARK_COLUMNS_READ:  Means a bit in read set is set to inform handler

	                that the field is to be read. If field list contains

                        duplicates, then session->dup_field is set to point

                        to the last found duplicate.

    MARK_COLUMNS_WRITE: Means a bit is set in write set to inform handler

			that it needs to update this field in write_row

                        and update_row.

  */

  enum enum_mark_columns mark_used_columns;

  LEX *lex;                                     // parse tree descriptor

  /*

    Points to the query associated with this statement. It's const, but

    we need to declare it char * because all table handlers are written

    in C and need to point to it.

    Note that (A) if we set query = NULL, we must at the same time set

    query_length = 0, and protect the whole operation with the

    LOCK_thread_count mutex. And (B) we are ONLY allowed to set query to a

    non-NULL value if its previous value is NULL. We do not need to protect

    operation (B) with any mutex. To avoid crashes in races, if we do not

    know that session->query cannot change at the moment, one should print

    session->query like this:

      (1) reserve the LOCK_thread_count mutex;

      (2) check if session->query is NULL;

      (3) if not NULL, then print at most session->query_length characters from

      it. We will see the query_length field as either 0, or the right value

      for it.

    Assuming that the write and read of an n-bit memory field in an n-bit

    computer is atomic, we can avoid races in the above way.

    This printing is needed at least in SHOW PROCESSLIST and SHOW INNODB

    STATUS.

  */

  char *query;

  uint32_t query_length;                          // current query length

  /**

    Name of the current (default) database.

    If there is the current (default) database, "db" contains its name. If

    there is no current (default) database, "db" is NULL and "db_length" is

    0. In other words, "db", "db_length" must either be NULL, or contain a

    valid database name.

    @note this attribute is set and alloced by the slave SQL thread (for

    the Session of that thread); that thread is (and must remain, for now) the

    only responsible for freeing this member.

  */

  char *db;

  uint32_t db_length;

public:

  /* This constructor is called for backup statements */

  Statement() {}

  Statement(LEX *lex_arg, MEM_ROOT *mem_root_arg, ulong id_arg);

  ~Statement() {}

};

struct st_savepoint {

  struct st_savepoint *prev;

  char                *name;

  uint32_t                 length;

  Ha_trx_info         *ha_list;

};

extern pthread_mutex_t LOCK_xid_cache;

extern HASH xid_cache;

#include <drizzled/security_context.h>

#include <drizzled/open_tables_state.h>

#include <drizzled/internal_error_handler.h> 

#include <drizzled/diagnostics_area.h> 

/**

  Storage engine specific thread local data.

*/

struct Ha_data

{

  /**

    Storage engine specific thread local data.

    Lifetime: one user connection.

  */

  void *ha_ptr;

  /**

    0: Life time: one statement within a transaction. If @@autocommit is

    on, also represents the entire transaction.

    @sa trans_register_ha()

    1: Life time: one transaction within a connection.

    If the storage engine does not participate in a transaction,

    this should not be used.

    @sa trans_register_ha()

  */

  Ha_trx_info ha_info[2];

  Ha_data() :ha_ptr(NULL) {}

};

class Session :public Statement, public Open_tables_state

{

public:

  /*

    Constant for Session::where initialization in the beginning of every query.

    It's needed because we do not save/restore Session::where normally during

    primary (non subselect) query execution.

  */

  static const char * const DEFAULT_WHERE;

  MEM_ROOT warn_root;			// For warnings and errors

  Protocol *protocol;			// Current protocol

  Protocol_text   protocol_text;	// Normal protocol

  char    compression;

  HASH    user_vars;			// hash for user variables

  String  packet;			// dynamic buffer for network I/O

  String  convert_buffer;               // buffer for charset conversions

  struct  system_variables variables;	// Changeable local variables

  struct  system_status_var status_var; // Per thread statistic vars

  struct  system_status_var *initial_status_var; /* used by show status */

  THR_LOCK_INFO lock_info;              // Locking info of this thread

  THR_LOCK_OWNER main_lock_id;          // To use for conventional queries

  THR_LOCK_OWNER *lock_id;              // If not main_lock_id, points to

                                        // the lock_id of a cursor.

  pthread_mutex_t LOCK_delete;		// Locked before session is deleted

  char process_list_info[PROCESS_LIST_WIDTH];

  /*

    A pointer to the stack frame of handle_one_connection(),

    which is called first in the thread for handling a client

  */

  char	  *thread_stack;

  /**

    Currently selected catalog.

  */

  char *catalog;

  /**

    @note

    Some members of Session (currently 'Statement::db',

    'catalog' and 'query')  are set and alloced by the slave SQL thread

    (for the Session of that thread); that thread is (and must remain, for now)

    the only responsible for freeing these 3 members. If you add members

    here, and you add code to set them in replication, don't forget to

    free_them_and_set_them_to_0 in replication properly. For details see

    the 'err:' label of the handle_slave_sql() in sql/slave.cc.

    @see handle_slave_sql

  */

  Security_context security_ctx;

  /*

    Points to info-string that we show in SHOW PROCESSLIST

    You are supposed to call Session_SET_PROC_INFO only if you have coded

    a time-consuming piece that MySQL can get stuck in for a long time.

    Set it using the  session_proc_info(Session *thread, const char *message)

    macro/function.

  */

  void        set_proc_info(const char *info) { proc_info= info; }

  const char* get_proc_info() const { return proc_info; }

  /*

    Used in error messages to tell user in what part of MySQL we found an

    error. E. g. when where= "having clause", if fix_fields() fails, user

    will know that the error was in having clause.

  */

  const char *where;

  double tmp_double_value;                    /* Used in set_var.cc */

  ulong client_capabilities;		/* What the client supports */

  ulong max_client_packet_length;

  /*

    One thread can hold up to one named user-level lock. This variable

    points to a lock object if the lock is present. See item_func.cc and

    chapter 'Miscellaneous functions', for functions GET_LOCK, RELEASE_LOCK.

  */

  uint32_t dbug_sentry; // watch out for memory corruption

  struct st_my_thread_var *mysys_var;

  /*

    Type of current query: COM_STMT_PREPARE, COM_QUERY, etc. Set from

    first byte of the packet in executeStatement()

  */

  enum enum_server_command command;

  uint32_t     server_id;

  uint32_t     file_id;			// for LOAD DATA INFILE

  /* remote (peer) port */

  uint16_t peer_port;

  time_t     start_time, user_time;

  uint64_t  connect_utime, thr_create_utime; // track down slow pthread_create

  uint64_t  start_utime, utime_after_lock;

  thr_lock_type update_lock_default;

  /*

    Both of the following container points in session will be converted to an API.

  */

  /* container for handler's private per-connection data */

  Ha_data ha_data[MAX_HA];

  /* container for replication data */

  void *replication_data;

  inline void setReplicationData (void *data) { replication_data= data; }

  inline void *getReplicationData () { return replication_data; }

  /* Place to store various things */

  void *session_marker;

  void set_server_id(uint32_t sid) { server_id = sid; }

public:

  struct st_transactions {

    SAVEPOINT *savepoints;

    Session_TRANS all;			// Trans since BEGIN WORK

    Session_TRANS stmt;			// Trans for current statement

    bool on;                            // see ha_enable_transaction()

    XID_STATE xid_state;

    /*

       Tables changed in transaction (that must be invalidated in query cache).

       List contain only transactional tables, that not invalidated in query

       cache (instead of full list of changed in transaction tables).

    */

    CHANGED_TableList* changed_tables;

    MEM_ROOT mem_root; // Transaction-life memory allocation pool

    void cleanup()

    {

      changed_tables= 0;

      savepoints= 0;

      free_root(&mem_root,MYF(MY_KEEP_PREALLOC));

    }

    st_transactions()

    {

      memset(this, 0, sizeof(*this));

      xid_state.xid.null();

      init_sql_alloc(&mem_root, ALLOC_ROOT_MIN_BLOCK_SIZE, 0);

    }

  } transaction;

  Field      *dup_field;

  sigset_t signals;

  /* Tells if LAST_INSERT_ID(#) was called for the current statement */

  bool arg_of_last_insert_id_function;

  /*

    ALL OVER THIS FILE, "insert_id" means "*automatically generated* value for

    insertion into an auto_increment column".

  */

  /*

    This is the first autogenerated insert id which was *successfully*

    inserted by the previous statement (exactly, if the previous statement

    didn't successfully insert an autogenerated insert id, then it's the one

    of the statement before, etc).

    It can also be set by SET LAST_INSERT_ID=# or SELECT LAST_INSERT_ID(#).

    It is returned by LAST_INSERT_ID().

  */

  uint64_t  first_successful_insert_id_in_prev_stmt;

  /*

    This is the first autogenerated insert id which was *successfully*

    inserted by the current statement. It is maintained only to set

    first_successful_insert_id_in_prev_stmt when statement ends.

  */

  uint64_t  first_successful_insert_id_in_cur_stmt;

  /*

    We follow this logic:

    - when stmt starts, first_successful_insert_id_in_prev_stmt contains the

    first insert id successfully inserted by the previous stmt.

    - as stmt makes progress, handler::insert_id_for_cur_row changes;

    every time get_auto_increment() is called,

    auto_inc_intervals_in_cur_stmt_for_binlog is augmented with the

    reserved interval (if statement-based binlogging).

    - at first successful insertion of an autogenerated value,

    first_successful_insert_id_in_cur_stmt is set to

    handler::insert_id_for_cur_row.

    - when stmt goes to binlog,

    auto_inc_intervals_in_cur_stmt_for_binlog is binlogged if

    non-empty.

    - when stmt ends, first_successful_insert_id_in_prev_stmt is set to

    first_successful_insert_id_in_cur_stmt.

  */

  /*

    List of auto_increment intervals reserved by the thread so far, for

    storage in the statement-based binlog.

    Note that its minimum is not first_successful_insert_id_in_cur_stmt:

    assuming a table with an autoinc column, and this happens:

    INSERT INTO ... VALUES(3);

    SET INSERT_ID=3; INSERT IGNORE ... VALUES (NULL);

    then the latter INSERT will insert no rows

    (first_successful_insert_id_in_cur_stmt == 0), but storing "INSERT_ID=3"

    in the binlog is still needed; the list's minimum will contain 3.

  */

  Discrete_intervals_list auto_inc_intervals_in_cur_stmt_for_binlog;

  /* Used by replication and SET INSERT_ID */

  Discrete_intervals_list auto_inc_intervals_forced;

  /*

    There is BUG#19630 where statement-based replication of stored

    functions/triggers with two auto_increment columns breaks.

    We however ensure that it works when there is 0 or 1 auto_increment

    column; our rules are

    a) on master, while executing a top statement involving substatements,

    first top- or sub- statement to generate auto_increment values wins the

    exclusive right to see its values be written to binlog (the write

    will be done by the statement or its caller), and the losers won't see

    their values be written to binlog.

    b) on slave, while replicating a top statement involving substatements,

    first top- or sub- statement to need to read auto_increment values from

    the master's binlog wins the exclusive right to read them (so the losers

    won't read their values from binlog but instead generate on their own).

    a) implies that we mustn't backup/restore

    auto_inc_intervals_in_cur_stmt_for_binlog.

    b) implies that we mustn't backup/restore auto_inc_intervals_forced.

    If there are more than 1 auto_increment columns, then intervals for

    different columns may mix into the

    auto_inc_intervals_in_cur_stmt_for_binlog list, which is logically wrong,

    but there is no point in preventing this mixing by preventing intervals

    from the secondly inserted column to come into the list, as such

    prevention would be wrong too.

    What will happen in the case of

    INSERT INTO t1 (auto_inc) VALUES(NULL);

    where t1 has a trigger which inserts into an auto_inc column of t2, is

    that in binlog we'll store the interval of t1 and the interval of t2 (when

    we store intervals, soon), then in slave, t1 will use both intervals, t2

    will use none; if t1 inserts the same number of rows as on master,

    normally the 2nd interval will not be used by t1, which is fine. t2's

    values will be wrong if t2's internal auto_increment counter is different

    from what it was on master (which is likely). In 5.1, in mixed binlogging

    mode, row-based binlogging is used for such cases where two

    auto_increment columns are inserted.

  */

  inline void record_first_successful_insert_id_in_cur_stmt(uint64_t id_arg)

  {

    if (first_successful_insert_id_in_cur_stmt == 0)

      first_successful_insert_id_in_cur_stmt= id_arg;

  }

  inline uint64_t read_first_successful_insert_id_in_prev_stmt(void)

  {

    return first_successful_insert_id_in_prev_stmt;

  }

  /*

    Used by Intvar_log_event::do_apply_event() and by "SET INSERT_ID=#"

    (mysqlbinlog). We'll soon add a variant which can take many intervals in

    argument.

  */

  inline void force_one_auto_inc_interval(uint64_t next_id)

  {

    auto_inc_intervals_forced.empty(); // in case of multiple SET INSERT_ID

    auto_inc_intervals_forced.append(next_id, UINT64_MAX, 0);

  }

  uint64_t  limit_found_rows;

  uint64_t  options;           /* Bitmap of states */

  int64_t   row_count_func;    /* For the ROW_COUNT() function */

  ha_rows    cuted_fields;

  /*

    number of rows we actually sent to the client, including "synthetic"

    rows in ROLLUP etc.

  */

  ha_rows    sent_row_count;

  /*

    number of rows we read, sent or not, including in create_sort_index()

  */

  ha_rows    examined_row_count;

  /*

    The set of those tables whose fields are referenced in all subqueries

    of the query.

    TODO: possibly this it is incorrect to have used tables in Session because

    with more than one subquery, it is not clear what does the field mean.

  */

  table_map  used_tables;

  const CHARSET_INFO *db_charset;

  /*

    FIXME: this, and some other variables like 'count_cuted_fields'

    maybe should be statement/cursor local, that is, moved to Statement

    class. With current implementation warnings produced in each prepared

    statement/cursor settle here.

  */

  List	     <DRIZZLE_ERROR> warn_list;

  uint32_t   warn_count[(uint32_t) DRIZZLE_ERROR::WARN_LEVEL_END];

  uint32_t   total_warn_count;

  Diagnostics_area main_da;

  /*

    Id of current query. Statement can be reused to execute several queries

    query_id is global in context of the whole MySQL server.

    ID is automatically generated from mutex-protected counter.

    It's used in handler code for various purposes: to check which columns

    from table are necessary for this select, to check if it's necessary to

    update auto-updatable fields (like auto_increment and timestamp).

  */

  query_id_t query_id, warn_id;

  ulong      col_access;

#ifdef ERROR_INJECT_SUPPORT

  ulong      error_inject_value;

#endif

  /* Statement id is thread-wide. This counter is used to generate ids */

  ulong      statement_id_counter;

  ulong	     rand_saved_seed1, rand_saved_seed2;

  /*

    Row counter, mainly for errors and warnings. Not increased in

    create_sort_index(); may differ from examined_row_count.

  */

  ulong      row_count;

  pthread_t  real_id;                           /* For debugging */

  my_thread_id  thread_id;

  uint	     tmp_table, global_read_lock;

  uint	     server_status,open_options;

  uint32_t       select_number;             //number of select (used for EXPLAIN)

  /* variables.transaction_isolation is reset to this after each commit */

  enum_tx_isolation session_tx_isolation;

  enum_check_fields count_cuted_fields;

  enum killed_state

  {

    NOT_KILLED,

    KILL_BAD_DATA,

    KILL_CONNECTION,

    KILL_QUERY,

    KILLED_NO_VALUE      /* means neither of the states */

  };

  killed_state volatile killed;

  bool	     some_tables_deleted;

  bool       last_cuted_field;

  bool	     no_errors, password;

  /**

    Set to true if execution of the current compound statement

    can not continue. In particular, disables activation of

    CONTINUE or EXIT handlers of stored routines.

    Reset in the end of processing of the current user request, in

    @see mysql_reset_session_for_next_command().

  */

  bool is_fatal_error;

  /**

    Set by a storage engine to request the entire

    transaction (that possibly spans multiple engines) to

    rollback. Reset in ha_rollback.

  */

  bool       transaction_rollback_request;

  /**

    true if we are in a sub-statement and the current error can

    not be safely recovered until we left the sub-statement mode.

    In particular, disables activation of CONTINUE and EXIT

    handlers inside sub-statements. E.g. if it is a deadlock

    error and requires a transaction-wide rollback, this flag is

    raised (traditionally, MySQL first has to close all the reads

    via @see handler::ha_index_or_rnd_end() and only then perform

    the rollback).

    Reset to false when we leave the sub-statement mode.

  */

  bool       is_fatal_sub_stmt_error;

  /* for IS NULL => = last_insert_id() fix in remove_eq_conds() */

  bool       substitute_null_with_insert_id;

  bool	     in_lock_tables;

  bool       cleanup_done;

  /**  is set if some thread specific value(s) used in a statement. */

  bool       thread_specific_used;

  bool	     charset_is_system_charset, charset_is_collation_connection;

  bool       charset_is_character_set_filesystem;

  bool	     abort_on_warning;

  bool 	     got_warning;       /* Set on call to push_warning() */

  bool	     no_warnings_for_error; /* no warnings on call to my_error() */

  /* set during loop of derived table processing */

  bool       derived_tables_processing;

  bool    tablespace_op;	/* This is true in DISCARD/IMPORT TABLESPACE */

  /* Used by the sys_var class to store temporary values */

  union

  {

    bool   bool_value;

    uint32_t  uint32_t_value;

    long      long_value;

    ulong     ulong_value;

    uint64_t uint64_t_value;

  } sys_var_tmp;

  /**

    Character input stream consumed by the lexical analyser,

    used during parsing.

    Note that since the parser is not re-entrant, we keep only one input

    stream here. This member is valid only when executing code during parsing,

    and may point to invalid memory after that.

  */

  Lex_input_stream *m_lip;

  Session();

  ~Session();

  void init(void);

  /*

    Initialize memory roots necessary for query processing and (!)

    pre-allocate memory for it. We can't do that in Session constructor because

    there are use cases (acl_init, watcher threads,

    killing mysqld) where it's vital to not allocate excessive and not used

    memory. Note, that we still don't return error from init_for_queries():

    if preallocation fails, we should notice that at the first call to

    alloc_root.

  */

  void init_for_queries();

  void cleanup(void);

  void cleanup_after_query();

  bool store_globals();

  void awake(Session::killed_state state_to_set);

  /**

   * Pulls thread-specific variables into Session state.

   *

   * Returns true most times, or false if there was a problem

   * allocating resources for thread-specific storage.

   *

   * @TODO Kill this.  It's not necessary once my_thr_init() is bye bye.

   *

   */

  bool initGlobals();

  /**

   * Initializes the Session to handle queries.

   */

  void prepareForQueries();

  /**

   * Executes a single statement received from the 

   * client connection.

   *

   * Returns true if the statement was successful, or false 

   * otherwise.