mariadb-columnstore-engine/dbcon/execplan/sessionmanager.h

/* Copyright (C) 2014 InfiniDB, Inc.

   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 Street, Fifth Floor, Boston,
   MA 02110-1301, USA. */

/******************************************************************************
 * $Id: sessionmanager.h 9215 2013-01-24 18:40:12Z pleblanc $
 *
 *****************************************************************************/

/** @file
 * class SessionManager interface
 */

#pragma once

#include "calpontsystemcatalog.h"
#include "brm.h"

namespace execplan
{
/** @brief Issues transaction IDs and keeps track of the current system-wide version ID.
 *
 * This class's primary purpose is to keep track of the current system-wide version ID and issue transaction
 * IDs. It can be used simultaneously by multiple threads and processes.
 *
 * It uses system-wide semaphores and shared memory segments for IPC.
 * It allocates both if they don't already exist, but it only deallocates
 * the shmseg (saves it to a file so state isn't lost).  It may be a waste of
 * CPU time to deallocate either while the system is running.  It may be more
 * appropriate to do that in the DB shut down script.
 *
 * Note: Added a macro 'DESTROYSHMSEG' which enables/disables the code to load/save
 * and deallocate the shared memory segment.
 *
 * This class uses 3 parameters from the Columnstore.xml file:
 * SessionManager/MaxConcurrentTransactions: defines how many active transactions the
 * 		system should support.  When a new request comes in and there are already
 * 		MaxConcurrentTransactions active, the new request blocks by default.  The
 * 		default value is 1000.
 * SessionManager/SharedMemoryTmpFile: the file to store the shared memory segment
 * 		data in between invocations if DESTROYSHMSEG is defined below.  The
 * 		default is /tmp/ColumnstoreShm.
 * SessionManager/TxnIDFile: the file to store the last transaction ID issued
 */

/*
 * Define DESTROYSHMSEG if the SM should deallocate the shared memory segment
 * after the last reference has died.  This also enables the load/save
 * operations.  If it is undefined, the segment is never deallocated
 * by SM, and is therefore more efficient between instances.
 * NOTE: It seems that valgrind doesn't work well with shared memory segments.
 * Specifically, when the code executes shmctl(IPC_RMID), which normally means
 * "destroy the segment when refcount == 0", the segment is destroyed
 * immediately, causing all subsequent references to fail.  This only affects
 * 'leakcheck'.
 */
// #define DESTROYSHMSEG

class SessionManager
{
 public:
  /** @brief SID = Session ID */
  typedef uint32_t SID;

  /** @brief Constructor
   *
   * This sets up the shared memory segment & semaphores used by this
   * instance.  No additional set-up calls are necessary.
   * @note throws ios_base::failure on file IO error, runtime_error for
   * other types of errors.  It might be worthwhile to define additional
   * exceptions for all the different types of failures that can happen
   * here.
   */
  SessionManager();
  SessionManager(const SessionManager&);

  /** @brief Constructor for use during debugging only
   *
   * This constructor is only used to grab the semaphores & reset them
   * if they exist.  It does not attach the shared memory segment,
   * and no operation other than reset() should be performed on a
   * SessionManager instantiated with this.
   */
  explicit SessionManager(bool nolock);

  /** @brief Destructor
   *
   * This detaches the shared memory segment.  If DESTROYSHMSEG is defined and this
   * is the last reference to it, it will be saved to disk and destroyed.
   * It does not destroy the semaphores.  Those persist until the system
   * is shut down.
   */
  virtual ~SessionManager();

  /** @brief Gets the current version ID
   *
   * Gets the current version ID.
   */
  const BRM::QueryContext verID();

  /** @brief Gets the current systemcatalog version ID
   *
   * Gets the current systemcatalog version ID.
   */
  const BRM::QueryContext sysCatVerID();

  /** @brief Gets a new Transaction ID
   *
   * Makes a new Transaction ID, associates it with the given session
   * and increments the system-wide version ID
   * @note This blocks until (# active transactions) \< MaxTxns unless block == false
   * @note Throws runtime_error on semaphore-related error
   * @note This will always return a valid TxnID unless block == false, in which case
   * it will return a valid TxnID iff it doesn't have to block.
   * @param session The session ID to associate with the transaction ID
   * @param block If true, this will block until there is an available slot, otherwise
   * it will return a TxnID marked invalid, signifying that it could not start a new transaction
   * @return The new transaction ID.
   */
  const BRM::TxnID newTxnID(const SID session, bool block = true, bool isDDL = false);

  /** @brief Record that a transaction has been committed
   *
   * Record that a transaction has been committed.
   * @note Throws runtime_error on a semaphore-related error, invalid_argument
   * when txnid can't be found
   * @param txnid The committed transaction ID.  This is marked invalid
   * on return.
   */
  void committed(BRM::TxnID& txnid);

  /** @brief Record that a transaction has been rolled back
   *
   * Record that a transaction has been rolled back.
   * @note Throws runtime_error on a semaphore-related error, invalid_argument
   * when txnid can't be found
   * @param txnid The rolled back transaction ID.  This is marked invalid
   * on return.
   */
  void rolledback(BRM::TxnID& txnid);

  /** @brief Gets the transaction ID associated with a given session ID
   *
   * Gets the transaction ID associated with a given session ID.
   * @note Throws runtime_error on a semaphore-related error
   * @param session The session ID
   * @return A valid transaction ID if there's an association; an invalid
   * one if there isn't.
   */
  const BRM::TxnID getTxnID(const SID session);

  /** @brief Gets an array containing all active SID-TID associations
   *
   * Gets an array containing the SID-TID associations of all active
   * transactions.  This is intended to be used by another object
   * that can determine which sessions are still live and which
   * transactions need to go away.
   * @note Throws runtime_error on a semaphore-related error
   * @param len (out) the length of the array
   * @return A pointer to the array.  Note: The caller is responsible for
   * deallocating it.  Use delete[].
   */
  std::shared_ptr<BRM::SIDTIDEntry[]> SIDTIDMap(int& len);

  /** @brief Returns a unique uint32_t.  It eventually wraps around, but who cares.
   *
   * This returns a "unique" uint32_t for when we need such a thing.  The current
   * usage is to get a unique identifier for each BPPJL and its associated BPP
   * object on the PM.
   * @return A "unique" uint32_t.
   */
  uint32_t getUnique32();

  /** @brief Returns the number of active transactions.  Only useful in testing.
   *
   * This returns the number of active transactions and verifies it against
   * the transaction semaphore's value and the value reported by shared->txnCount.
   * @note Throws logic_error if there's a mismatch, runtime_error on a
   * semaphore operation error.
   * @return The number of active transactions.
   */
  int verifySize();

  /** @brief Resets the semaphores to their original state.  For testing only.
   *
   * Resets the semaphores to their original state.  For testing only.
   */
  void reset();

  std::string getTxnIDFilename() const;

  bool checkActiveTransaction(const SID sessionId, bool& bIsDbrmUp, BRM::SIDTIDEntry& blocker);
  bool isTransactionActive(const SID sessionId, bool& bIsDbrmUp);

 private:
  BRM::DBRM dbrm;
  std::string txnidFilename;
};

}  // namespace execplan