mariadb/wsrep/wsrep_api.h

/* Copyright (C) 2009-2013 Codership Oy <info@codership.com>

   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.
 */

/*!
  @file wsrep API declaration.

  HOW TO READ THIS FILE.

  Due to C language rules this header layout doesn't lend itself to intuitive
  reading. So here's the scoop: in the end this header declares two main types:

  * struct wsrep_init_args

  and

  * struct wsrep

  wsrep_init_args contains initialization parameters for wsrep provider like
  names, addresses, etc. and pointers to callbacks. The callbacks will be called
  by provider when it needs to do something application-specific, like log a
  message or apply a writeset. It should be passed to init() call from
  wsrep API. It is an application part of wsrep API contract.

  struct wsrep is the interface to wsrep provider. It contains all wsrep API
  calls. It is a provider part of wsrep API contract.

  Finally, wsrep_load() method loads (dlopens) wsrep provider library. It is
  defined in wsrep_loader.c unit and is part of libwsrep.a (which is not a
  wsrep provider, but a convenience library).

  wsrep_unload() does the reverse.

*/
#ifndef WSREP_H
#define WSREP_H

#include <stdint.h>
#include <stdbool.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>

#ifdef __cplusplus
extern "C" {
#endif

/**************************************************************************
 *                                                                        *
 *                       wsrep replication API                            *
 *                                                                        *
 **************************************************************************/

#define WSREP_INTERFACE_VERSION "25"

/*! Empty backend spec */
#define WSREP_NONE "none"


/*!
 * @brief log severity levels, passed as first argument to log handler
 */
typedef enum wsrep_log_level
{
    WSREP_LOG_FATAL, //!< Unrecoverable error, application must quit.
    WSREP_LOG_ERROR, //!< Operation failed, must be repeated.
    WSREP_LOG_WARN,  //!< Unexpected condition, but no operational failure.
    WSREP_LOG_INFO,  //!< Informational message.
    WSREP_LOG_DEBUG  //!< Debug message. Shows only of compiled with debug.
} wsrep_log_level_t;

/*!
 * @brief error log handler
 *
 *        All messages from wsrep provider are directed to this
 *        handler, if present.
 *
 * @param level   log level
 * @param message log message
 */
typedef void (*wsrep_log_cb_t)(wsrep_log_level_t, const char *);


/*!
 *  Certain provider capabilities application may want to know about
 */
#define WSREP_CAP_MULTI_MASTER          ( 1ULL << 0 )
#define WSREP_CAP_CERTIFICATION         ( 1ULL << 1 )
#define WSREP_CAP_PARALLEL_APPLYING     ( 1ULL << 2 )
#define WSREP_CAP_TRX_REPLAY            ( 1ULL << 3 )
#define WSREP_CAP_ISOLATION             ( 1ULL << 4 )
#define WSREP_CAP_PAUSE                 ( 1ULL << 5 )
#define WSREP_CAP_CAUSAL_READS          ( 1ULL << 6 )
#define WSREP_CAP_CAUSAL_TRX            ( 1ULL << 7 )
#define WSREP_CAP_INCREMENTAL_WRITESET  ( 1ULL << 8 )
#define WSREP_CAP_SESSION_LOCKS         ( 1ULL << 9 )
#define WSREP_CAP_DISTRIBUTED_LOCKS     ( 1ULL << 10 )
#define WSREP_CAP_CONSISTENCY_CHECK     ( 1ULL << 11 )
#define WSREP_CAP_UNORDERED             ( 1ULL << 12 )
#define WSREP_CAP_ANNOTATION            ( 1ULL << 13 )
#define WSREP_CAP_PREORDERED            ( 1ULL << 14 )


/*!
 *  Writeset flags
 *
 * COMMIT       the writeset and all preceding writesets must be committed
 * ROLLBACK     all preceding writesets in a transaction must be rolled back
 * ISOLATION    the writeset must be applied AND committed in isolation
 * PA_UNSAFE    the writeset cannot be applied in parallel
 * COMMUTATIVE  the order in which the writeset is applied does not matter
 * NATIVE       the writeset contains another writeset in this provider format
 *
 * Note that some of the flags are mutually exclusive (e.g. COMMIT and
 * ROLLBACK).
 */
#define WSREP_FLAG_COMMIT               ( 1ULL << 0 )
#define WSREP_FLAG_ROLLBACK             ( 1ULL << 1 )
#define WSREP_FLAG_ISOLATION            ( 1ULL << 2 )
#define WSREP_FLAG_PA_UNSAFE            ( 1ULL << 3 )
#define WSREP_FLAG_COMMUTATIVE          ( 1ULL << 4 )
#define WSREP_FLAG_NATIVE               ( 1ULL << 5 )


typedef uint64_t wsrep_trx_id_t;  //!< application transaction ID
typedef uint64_t wsrep_conn_id_t; //!< application connection ID
typedef int64_t  wsrep_seqno_t;   //!< sequence number of a writeset, etc.
#ifdef __cplusplus
typedef bool     wsrep_bool_t;
#else
typedef _Bool    wsrep_bool_t;    //!< should be the same as standard (C99) bool
#endif /* __cplusplus */

/*! undefined seqno */
#define WSREP_SEQNO_UNDEFINED (-1)


/*! wsrep provider status codes */
typedef enum wsrep_status
{
    WSREP_OK = 0,          //!< success
    WSREP_WARNING,         //!< minor warning, error logged
    WSREP_TRX_MISSING,     //!< transaction is not known by wsrep
    WSREP_TRX_FAIL,        //!< transaction aborted, server can continue
    WSREP_BF_ABORT,        //!< trx was victim of brute force abort
    WSREP_SIZE_EXCEEDED,   //!< data exceeded maximum supported size
    WSREP_CONN_FAIL,       //!< error in client connection, must abort
    WSREP_NODE_FAIL,       //!< error in node state, wsrep must reinit
    WSREP_FATAL,           //!< fatal error, server must abort
    WSREP_NOT_IMPLEMENTED  //!< feature not implemented
} wsrep_status_t;


/*! wsrep callbacks status codes */
typedef enum wsrep_cb_status
{
    WSREP_CB_SUCCESS =  0, //!< success (as in "not critical failure")
    WSREP_CB_FAILURE       //!< critical failure (consistency violation)
    /* Technically, wsrep provider has no use for specific failure codes since
     * there is nothing it can do about it but abort execution. Therefore any
     * positive number shall indicate a critical failure. Optionally that value
     * may be used by provider to come to a consensus about state consistency
     * in a group of nodes. */
} wsrep_cb_status_t;


/*!
 * UUID type - for all unique IDs
 */
typedef struct wsrep_uuid {
    uint8_t data[16];
} wsrep_uuid_t;

/*! Undefined UUID */
static const wsrep_uuid_t WSREP_UUID_UNDEFINED = {{0,}};

/*! UUID string representation length, terminating '\0' not included */
#define WSREP_UUID_STR_LEN 36

/*!
 * Scan UUID from string
 * @return length of UUID string representation or negative error code
 */
extern int
wsrep_uuid_scan (const char* str, size_t str_len, wsrep_uuid_t* uuid);

/*!
 * Print UUID to string
 * @return length of UUID string representation or negative error code
 */
extern int
wsrep_uuid_print (const wsrep_uuid_t* uuid, char* str, size_t str_len);

#define WSREP_MEMBER_NAME_LEN 32  //!< maximum logical member name length
#define WSREP_INCOMING_LEN    256 //!< max Domain Name length + 0x00


/*!
 * Global transaction identifier
 */
typedef struct wsrep_gtid
{
    wsrep_uuid_t  uuid;  /*!< History UUID */
    wsrep_seqno_t seqno; /*!< Sequence number */
} wsrep_gtid_t;

/*! Undefined GTID */
static const wsrep_gtid_t WSREP_GTID_UNDEFINED = {{{0, }}, -1};

/*! Minimum number of bytes guaranteed to store GTID string representation,
 * terminating '\0' not included (36 + 1 + 20) */
#define WSREP_GTID_STR_LEN 57


/*!
 * Scan GTID from string
 * @return length of GTID string representation or negative error code
 */
extern int
wsrep_gtid_scan(const char* str, size_t str_len, wsrep_gtid_t* gtid);

/*!
 * Print GTID to string
 * @return length of GTID string representation or negative error code
 */
extern int
wsrep_gtid_print(const wsrep_gtid_t* gtid, char* str, size_t str_len);


/*!
 * Transaction meta data
 */
typedef struct wsrep_trx_meta
{
    wsrep_gtid_t  gtid;       /*!< Global transaction identifier */
    wsrep_seqno_t depends_on; /*!< Sequence number part of the last transaction
                                   this transaction depends on */
} wsrep_trx_meta_t;


/*!
 * member status
 */
typedef enum wsrep_member_status {
    WSREP_MEMBER_UNDEFINED, //!< undefined state
    WSREP_MEMBER_JOINER,    //!< incomplete state, requested state transfer
    WSREP_MEMBER_DONOR,     //!< complete state, donates state transfer
    WSREP_MEMBER_JOINED,    //!< complete state
    WSREP_MEMBER_SYNCED,    //!< complete state, synchronized with group
    WSREP_MEMBER_ERROR,     //!< this and above is provider-specific error code
    WSREP_MEMBER_MAX
} wsrep_member_status_t;

/*!
 * static information about a group member (some fields are tentative yet)
 */
typedef struct wsrep_member_info {
    wsrep_uuid_t id;                           //!< group-wide unique member ID
    char         name[WSREP_MEMBER_NAME_LEN];  //!< human-readable name
    char         incoming[WSREP_INCOMING_LEN]; //!< address for client requests
} wsrep_member_info_t;

/*!
 * group status
 */
typedef enum wsrep_view_status {
    WSREP_VIEW_PRIMARY,      //!< primary group configuration (quorum present)
    WSREP_VIEW_NON_PRIMARY,  //!< non-primary group configuration (quorum lost)
    WSREP_VIEW_DISCONNECTED, //!< not connected to group, retrying.
    WSREP_VIEW_MAX
} wsrep_view_status_t;

/*!
 * view of the group
 */
typedef struct wsrep_view_info {
    wsrep_gtid_t        state_id;  //!< global state ID
    wsrep_seqno_t       view;      //!< global view number
    wsrep_view_status_t status;    //!< view status
    wsrep_bool_t        state_gap; //!< gap between global and local states
    int                 my_idx;    //!< index of this member in the view
    int                 memb_num;  //!< number of members in the view
    int                 proto_ver; //!< application protocol agreed on the view
    wsrep_member_info_t members[1];//!< array of member information
} wsrep_view_info_t;

/*!
 * Magic string to tell provider to engage into trivial (empty) state transfer.
 * No data will be passed, but the node shall be considered JOINED.
 * Should be passed in sst_req parameter of wsrep_view_cb_t.
 */
#define WSREP_STATE_TRANSFER_TRIVIAL "trivial"

/*!
 * Magic string to tell provider not to engage in state transfer at all.
 * The member will stay in WSREP_MEMBER_UNDEFINED state but will keep on
 * receiving all writesets.
 * Should be passed in sst_req parameter of wsrep_view_cb_t.
 */
#define WSREP_STATE_TRANSFER_NONE "none"

/*!
 * @brief group view handler
 *
 * This handler is called in total order corresponding to the group
 * configuration change. It is to provide a vital information about
 * new group view. If view info indicates existence of discontinuity
 * between group and member states, state transfer request message
 * should be filled in by the callback implementation.
 *
 * @note Currently it is assumed that sst_req is allocated using
 *       malloc()/calloc()/realloc() and it will be freed by
 *       wsrep implementation.
 *
 * @param app_ctx     application context
 * @param recv_ctx    receiver context
 * @param view        new view on the group
 * @param state       current state
 * @param state_len   lenght of current state
 * @param sst_req     location to store SST request
 * @param sst_req_len location to store SST request length or error code,
 *                    value of 0 means no SST.
 */
typedef enum wsrep_cb_status (*wsrep_view_cb_t) (
    void*                    app_ctx,
    void*                    recv_ctx,
    const wsrep_view_info_t* view,
    const char*              state,
    size_t                   state_len,
    void**                   sst_req,
    size_t*                  sst_req_len
);


/*!
 * @brief apply callback
 *
 * This handler is called from wsrep library to apply replicated writeset
 * Must support brute force applying for multi-master operation
 *
 * @param recv_ctx receiver context pointer provided by the application
 * @param data     data buffer containing the writeset
 * @param size     data buffer size
 * @param flags    WSREP_FLAG_... flags
 * @param meta     transaction meta data of the writeset to be applied
 *
 * @return success code:
 * @retval WSREP_OK
 * @retval WSREP_NOT_IMPLEMENTED appl. does not support the writeset format
 * @retval WSREP_ERROR failed to apply the writeset
 */
typedef enum wsrep_cb_status (*wsrep_apply_cb_t) (
    void*                   recv_ctx,
    const void*             data,
    size_t                  size,
    uint32_t                flags,
    const wsrep_trx_meta_t* meta
);


/*!
 * @brief commit callback
 *
 * This handler is called to commit the changes made by apply callback.
 *
 * @param recv_ctx receiver context pointer provided by the application
 * @param flags    WSREP_FLAG_... flags
 * @param meta     transaction meta data of the writeset to be committed
 * @param exit     set to true to exit recv loop
 * @param commit   true - commit writeset, false - rollback writeset
 *
 * @return success code:
 * @retval WSREP_OK
 * @retval WSREP_ERROR call failed
 */
typedef enum wsrep_cb_status (*wsrep_commit_cb_t) (
    void*                   recv_ctx,
    uint32_t                flags,
    const wsrep_trx_meta_t* meta,
    wsrep_bool_t*           exit,
    wsrep_bool_t            commit
);


/*!
 * @brief unordered callback
 *
 * This handler is called to execute unordered actions (actions that need not
 * to be executed in any particular order) attached to writeset.
 *
 * @param recv_ctx receiver context pointer provided by the application
 * @param data     data buffer containing the writeset
 * @param size     data buffer size
 */
typedef enum wsrep_cb_status (*wsrep_unordered_cb_t) (
    void*       recv_ctx,
    const void* data,
    size_t      size
);


/*!
 * @brief a callback to donate state snapshot
 *
 * This handler is called from wsrep library when it needs this node
 * to deliver state to a new cluster member.
 * No state changes will be committed for the duration of this call.
 * Wsrep implementation may provide internal state to be transmitted
 * to new cluster member for initial state.
 *
 * @param app_ctx   application context
 * @param recv_ctx  receiver context
 * @param msg       state transfer request message
 * @param msg_len   state transfer request message length
 * @param gtid      current state ID on this node
 * @param state     current wsrep internal state buffer
 * @param state_len current wsrep internal state buffer len
 * @param bypass    bypass snapshot transfer, only transfer uuid:seqno pair
 */
typedef enum wsrep_cb_status (*wsrep_sst_donate_cb_t) (
    void*               app_ctx,
    void*               recv_ctx,
    const void*         msg,
    size_t              msg_len,
    const wsrep_gtid_t* state_id,
    const char*         state,
    size_t              state_len,
    wsrep_bool_t        bypass
);


/*!
 * @brief a callback to signal application that wsrep state is synced
 *        with cluster
 *
 * This callback is called after wsrep library has got in sync with
 * rest of the cluster.
 *
 * @param app_ctx application context
 */
typedef void (*wsrep_synced_cb_t) (void* app_ctx);


/*!
 * Initialization parameters for wsrep provider.
 */
struct wsrep_init_args
{
    void* app_ctx;             //!< Application context for callbacks

    /* Configuration parameters */
    const char* node_name;     //!< Symbolic name of this node (e.g. hostname)
    const char* node_address;  //!< Address to be used by wsrep provider
    const char* node_incoming; //!< Address for incoming client connections
    const char* data_dir;      //!< Directory where wsrep files are kept if any
    const char* options;       //!< Provider-specific configuration string
    int         proto_ver;     //!< Max supported application protocol version

    /* Application initial state information. */
    const wsrep_gtid_t* state_id;    //!< Application state GTID
    const char*         state;       //!< Initial state for wsrep provider
    size_t              state_len;   //!< Length of state buffer

    /* Application callbacks */
    wsrep_log_cb_t        logger_cb;       //!< logging handler
    wsrep_view_cb_t       view_handler_cb; //!< group view change handler

    /* Applier callbacks */
    wsrep_apply_cb_t      apply_cb;        //!< apply  callback
    wsrep_commit_cb_t     commit_cb;       //!< commit callback
    wsrep_unordered_cb_t  unordered_cb;    //!< callback for unordered actions

    /* State Snapshot Transfer callbacks */
    wsrep_sst_donate_cb_t sst_donate_cb;   //!< starting to donate
    wsrep_synced_cb_t     synced_cb;       //!< synced with group
};


/*! Type of the stats variable value in struct wsrep_status_var */
typedef enum wsrep_var_type
{
    WSREP_VAR_STRING, //!< pointer to null-terminated string
    WSREP_VAR_INT64,  //!< int64_t
    WSREP_VAR_DOUBLE  //!< double
}
wsrep_var_type_t;

/*! Generalized stats variable representation */
struct wsrep_stats_var
{
    const char*      name;     //!< variable name
    wsrep_var_type_t type;     //!< variable value type
    union {
        int64_t     _int64;
        double      _double;
        const char* _string;
    } value;                   //!< variable value
};


/*! Abstract data buffer structure */
typedef struct wsrep_buf
{
    const void* ptr; /*!< Pointer to data buffer */
    size_t      len; /*!< Length of buffer */
} wsrep_buf_t;

/*! Key struct used to pass certification keys for transaction handling calls.
 *  A key consists of zero or more key parts. */
typedef struct wsrep_key
{
    const wsrep_buf_t* key_parts;     /*!< Array of key parts  */
    size_t             key_parts_num; /*!< Number of key parts */
} wsrep_key_t;

/*! Key type:
 *  EXCLUSIVE conflicts with any key type
 *  SEMI      reserved. If not supported, should be interpeted as EXCLUSIVE
 *  SHARED    conflicts only with EXCLUSIVE keys */
typedef enum wsrep_key_type
{
    WSREP_KEY_SHARED = 0,
    WSREP_KEY_SEMI,
    WSREP_KEY_EXCLUSIVE
} wsrep_key_type_t;

/*! Data type:
 *  ORDERED    state modification event that should be applied and committed
 *             in order.
 *  UNORDERED  some action that does not modify state and execution of which is
 *             optional and does not need to happen in order.
 *  ANNOTATION (human readable) writeset annotation. */
typedef enum wsrep_data_type
{
    WSREP_DATA_ORDERED = 0,
    WSREP_DATA_UNORDERED,
    WSREP_DATA_ANNOTATION
} wsrep_data_type_t;


/*! Transaction handle struct passed for wsrep transaction handling calls */
typedef struct wsrep_ws_handle
{
    wsrep_trx_id_t trx_id; //!< transaction ID
    void*          opaque; //!< opaque provider transaction context data
} wsrep_ws_handle_t;

/*!
 * @brief Helper method to reset trx writeset handle state when trx id changes
 *
 * Instead of passing wsrep_ws_handle_t directly to wsrep calls,
 * wrapping handle with this call offloads bookkeeping from
 * application.
 */
static inline wsrep_ws_handle_t* wsrep_ws_handle_for_trx(
    wsrep_ws_handle_t* ws_handle,
    wsrep_trx_id_t     trx_id)
{
    if (ws_handle->trx_id != trx_id)
    {
        ws_handle->trx_id = trx_id;
        ws_handle->opaque = NULL;
    }
    return ws_handle;
}


/*!
 *  A handle for processing preordered actions.
 *  Must be initialized to WSREP_PO_INITIALIZER before use.
 */
typedef struct wsrep_po_handle { void* opaque; } wsrep_po_handle_t;

static const wsrep_po_handle_t WSREP_PO_INITIALIZER = { NULL };


typedef struct wsrep wsrep_t;
/*!
 * wsrep interface for dynamically loadable libraries
 */
struct wsrep {

    const char *version; //!< interface version string

  /*!
   * @brief Initializes wsrep provider
   *
   * @param wsrep provider handle
   * @param args  wsrep initialization parameters
   */
    wsrep_status_t (*init)   (wsrep_t*                      wsrep,
                              const struct wsrep_init_args* args);

  /*!
   * @brief Returns provider capabilities flag bitmap
   *
   * @param wsrep provider handle
   */
    uint64_t (*capabilities) (wsrep_t* wsrep);

  /*!
   * @brief Passes provider-specific configuration string to provider.
   *
   * @param wsrep provider handle
   * @param conf  configuration string
   *
   * @retval WSREP_OK      configuration string was parsed successfully
   * @retval WSREP_WARNING could't not parse conf string, no action taken
   */
    wsrep_status_t (*options_set) (wsrep_t* wsrep, const char* conf);

  /*!
   * @brief Returns provider-specific string with current configuration values.
   *
   * @param wsrep provider handle
   *
   * @return a dynamically allocated string with current configuration
   *         parameter values
   */
    char*          (*options_get) (wsrep_t* wsrep);

  /*!
   * @brief Opens connection to cluster
   *
   * Returns when either node is ready to operate as a part of the clsuter
   * or fails to reach operating status.
   *
   * @param wsrep        provider handle
   * @param cluster_name unique symbolic cluster name
   * @param cluster_url  URL-like cluster address (backend://address)
   * @param state_donor  name of the node to be asked for state transfer.
   * @param bootstrap    a flag to request initialization of a new wsrep
   *                     service rather then a connection to the existing one.
   *                     clister_url may still carry important initialization
   *                     parameters, like backend spec and/or listen address.
   */
    wsrep_status_t (*connect) (wsrep_t*     wsrep,
                               const char*  cluster_name,
                               const char*  cluster_url,
                               const char*  state_donor,
                               wsrep_bool_t bootstrap);

  /*!
   * @brief Closes connection to cluster.
   *
   * If state_uuid and/or state_seqno is not NULL, will store final state
   * in there.
   *
   * @param wsrep this  wsrep handler
   */
    wsrep_status_t (*disconnect)(wsrep_t* wsrep);

  /*!
   * @brief start receiving replication events
   *
   * This function never returns
   *
   * @param wsrep provider handle
   * @param recv_ctx receiver context
   */
    wsrep_status_t (*recv)(wsrep_t* wsrep, void* recv_ctx);

  /*!
   * @brief Replicates/logs result of transaction to other nodes and allocates
   * required resources.
   *
   * Must be called before transaction commit. Returns success code, which
   * caller must check.
   * In case of WSREP_OK, starts commit critical section, transaction can
   * commit. Otherwise transaction must rollback.
   *
   * @param wsrep      provider handle
   * @param ws_handle  writeset of committing transaction
   * @param conn_id    connection ID
   * @param flags      fine tuning the replication WSREP_FLAG_*
   * @param meta       transaction meta data
   *
   * @retval WSREP_OK         cluster-wide commit succeeded
   * @retval WSREP_TRX_FAIL   must rollback transaction
   * @retval WSREP_CONN_FAIL  must close client connection
   * @retval WSREP_NODE_FAIL  must close all connections and reinit
   */
    wsrep_status_t (*pre_commit)(wsrep_t*                wsrep,
                                 wsrep_conn_id_t         conn_id,
                                 wsrep_ws_handle_t*      ws_handle,
                                 uint32_t                flags,
                                 wsrep_trx_meta_t*       meta);

  /*!
   * @brief Releases resources after transaction commit.
   *
   * Ends commit critical section.
   *
   * @param wsrep      provider handle
   * @param ws_handle  writeset of committing transaction
   * @retval WSREP_OK  post_commit succeeded
   */
    wsrep_status_t (*post_commit) (wsrep_t*            wsrep,
                                   wsrep_ws_handle_t*  ws_handle);

  /*!
   * @brief Releases resources after transaction rollback.
   *
   * @param wsrep      provider handle
   * @param ws_handle  writeset of committing transaction
   * @retval WSREP_OK  post_rollback succeeded
   */
    wsrep_status_t (*post_rollback)(wsrep_t*            wsrep,
                                    wsrep_ws_handle_t*  ws_handle);

  /*!
   * @brief Replay trx as a slave writeset
   *
   * If local trx has been aborted by brute force, and it has already
   * replicated before this abort, we must try if we can apply it as
   * slave trx. Note that slave nodes see only trx writesets and certification
   * test based on write set content can be different to DBMS lock conflicts.
   *
   * @param wsrep      provider handle
   * @param ws_handle  writeset of committing transaction
   * @param trx_ctx    transaction context
   *
   * @retval WSREP_OK         cluster commit succeeded
   * @retval WSREP_TRX_FAIL   must rollback transaction
   * @retval WSREP_BF_ABORT   brute force abort happened after trx replicated
   *                          must rollback transaction and try to replay
   * @retval WSREP_CONN_FAIL  must close client connection
   * @retval WSREP_NODE_FAIL  must close all connections and reinit
   */
    wsrep_status_t (*replay_trx)(wsrep_t*            wsrep,
                                 wsrep_ws_handle_t*  ws_handle,
                                 void*               trx_ctx);

  /*!
   * @brief Abort pre_commit() call of another thread.
   *
   * It is possible, that some high-priority transaction needs to abort
   * another transaction which is in pre_commit() call waiting for resources.
   *
   * The kill routine checks that abort is not attmpted against a transaction
   * which is front of the caller (in total order).
   *
   * @param wsrep      provider handle
   * @param bf_seqno   seqno of brute force trx, running this cancel
   * @param victim_trx transaction to be aborted, and which is committing
   *
   * @retval WSREP_OK       abort secceded
   * @retval WSREP_WARNING  abort failed
   */
    wsrep_status_t (*abort_pre_commit)(wsrep_t*       wsrep,
                                       wsrep_seqno_t  bf_seqno,
                                       wsrep_trx_id_t victim_trx);

  /*!
   * @brief Appends a row reference to transaction writeset
   *
   * Both copy flag and key_type can be ignored by provider (key type
   * interpreted as WSREP_KEY_EXCLUSIVE).
   *
   * @param wsrep      provider handle
   * @param ws_handle  writeset handle
   * @param keys       array of keys
   * @param count      length of the array of keys
   * @param type       type ot the key
   * @param copy       can be set to FALSE if keys persist through commit.
   */
    wsrep_status_t (*append_key)(wsrep_t*            wsrep,
                                 wsrep_ws_handle_t*  ws_handle,
                                 const wsrep_key_t*  keys,
                                 size_t              count,
                                 enum wsrep_key_type type,
                                 wsrep_bool_t        copy);

  /*!
   * @brief Appends data to transaction writeset
   *
   * This method can be called any time before commit and it
   * appends a number of data buffers to transaction writeset.
   *
   * Both copy and unordered flags can be ignored by provider.
   *
   * @param wsrep      provider handle
   * @param ws_handle  writeset handle
   * @param data       array of data buffers
   * @param count      buffer count
   * @param type       type of data
   * @param copy       can be set to FALSE if data persists through commit.
   */
    wsrep_status_t (*append_data)(wsrep_t*                wsrep,
                                  wsrep_ws_handle_t*      ws_handle,
                                  const struct wsrep_buf* data,
                                  size_t                  count,
                                  enum wsrep_data_type    type,
                                  wsrep_bool_t            copy);

  /*!
   * @brief Get causal ordering for read operation
   *
   * This call will block until causal ordering with all possible
   * preceding writes in the cluster is guaranteed. If pointer to
   * gtid is non-null, the call stores the global transaction ID
   * of the last transaction which is guaranteed to be ordered
   * causally before this call.
   *
   * @param wsrep provider handle
   * @param gtid  location to store GTID
   */
    wsrep_status_t (*causal_read)(wsrep_t* wsrep, wsrep_gtid_t* gtid);

  /*!
   * @brief Clears allocated connection context.
   *
   * Whenever a new connection ID is passed to wsrep provider through
   * any of the API calls, a connection context is allocated for this
   * connection. This call is to explicitly notify provider fo connection
   * closing.
   *
   * @param wsrep       provider handle
   * @param conn_id     connection ID
   * @param query       the 'set database' query
   * @param query_len   length of query (does not end with 0)
   */
    wsrep_status_t (*free_connection)(wsrep_t*        wsrep,
                                      wsrep_conn_id_t conn_id);

  /*!
   * @brief Replicates a query and starts "total order isolation" section.
   *
   * Replicates the action spec and returns success code, which caller must
   * check. Total order isolation continues until to_execute_end() is called.
   *
   * @param wsrep       provider handle
   * @param conn_id     connection ID
   * @param keys        array of keys
   * @param keys_num    lenght of the array of keys
   * @param action      action buffer array to be executed
   * @param count       action buffer count
   * @param meta        transaction meta data
   *
   * @retval WSREP_OK         cluster commit succeeded
   * @retval WSREP_CONN_FAIL  must close client connection
   * @retval WSREP_NODE_FAIL  must close all connections and reinit
   */
    wsrep_status_t (*to_execute_start)(wsrep_t*                wsrep,
                                       wsrep_conn_id_t         conn_id,
                                       const wsrep_key_t*      keys,
                                       size_t                  keys_num,
                                       const struct wsrep_buf* action,
                                       size_t                  count,
                                       wsrep_trx_meta_t*       meta);

  /*!
   * @brief Ends the total order isolation section.
   *
   * Marks the end of total order isolation. TO locks are freed
   * and other transactions are free to commit from this point on.
   *
   * @param wsrep provider handle
   * @param conn_id connection ID
   *
   * @retval WSREP_OK         cluster commit succeeded
   * @retval WSREP_CONN_FAIL  must close client connection
   * @retval WSREP_NODE_FAIL  must close all connections and reinit
   */
    wsrep_status_t (*to_execute_end)(wsrep_t* wsrep, wsrep_conn_id_t conn_id);

  /*!
   * @brief Collects preordered replication events into a writeset.
   *
   * @param wsrep   wsrep provider handle
   * @param handle  a handle associated with a given writeset
   * @param data    an array of data buffers.
   * @param count   length of data buffer array.
   * @param copy    whether provider needs to make a copy of events.
   *
   * @retval WSREP_OK         cluster-wide commit succeeded
   * @retval WSREP_TRX_FAIL   operation failed (e.g. trx size exceeded limit)
   * @retval WSREP_NODE_FAIL  must close all connections and reinit
   */
    wsrep_status_t (*preordered_collect) (wsrep_t*                 wsrep,
                                          wsrep_po_handle_t*       handle,
                                          const struct wsrep_buf*  data,
                                          size_t                   count,
                                          wsrep_bool_t             copy);

  /*!
   * @brief "Commits" preordered writeset to cluster.
   *
   * The contract is that the writeset will be committed in the same (partial)
   * order this method was called. Frees resources associated with the writeset
   * handle and reinitializes the handle.
   *
   * @param wsrep     wsrep provider handle
   * @param po_handle a handle associated with a given writeset
   * @param source_id ID of the event producer, also serves as the partial order
   *                  or stream ID - events with different source_ids won't be
   *                  ordered with respect to each other.
   * @param flags     WSREP_FLAG_... flags
   * @param pa_range  the number of preceding events this event can be processed
   *                  in parallel with. A value of 0 means strict serial
   *                  processing. Note: commits always happen in wsrep order.
   * @param commit    'true'  to commit writeset to cluster (replicate) or
   *                  'false' to rollback (cancel) the writeset.
   *
   * @retval WSREP_OK         cluster-wide commit succeeded
   * @retval WSREP_TRX_FAIL   operation failed (e.g. NON-PRIMARY component)
   * @retval WSREP_NODE_FAIL  must close all connections and reinit
   */
    wsrep_status_t (*preordered_commit)  (wsrep_t*             wsrep,
                                          wsrep_po_handle_t*   handle,
                                          const wsrep_uuid_t*  source_id,
                                          uint32_t             flags,
                                          int                  pa_range,
                                          wsrep_bool_t         commit);

  /*!
   * @brief Signals to wsrep provider that state snapshot has been sent to
   *        joiner.
   *
   * @param wsrep    provider handle
   * @param state_id state ID
   * @param rcode    0 or negative error code of the operation.
   */
    wsrep_status_t (*sst_sent)(wsrep_t*            wsrep,
                               const wsrep_gtid_t* state_id,
                               int                 rcode);

  /*!
   * @brief Signals to wsrep provider that new state snapshot has been received.
   *        May deadlock if called from sst_prepare_cb.
   *
   * @param wsrep     provider handle
   * @param state_id  state ID
   * @param state     initial state provided by SST donor
   * @param state_len length of state buffer
   * @param rcode     0 or negative error code of the operation.
   */
    wsrep_status_t (*sst_received)(wsrep_t*            wsrep,
                                   const wsrep_gtid_t* state_id,
                                   const void*         state,
                                   size_t              state_len,
                                   int                 rcode);


  /*!
   * @brief Generate request for consistent snapshot.
   *
   * If successfull, this call will generate internally SST request
   * which in turn triggers calling SST donate callback on the nodes
   * specified in donor_spec. If donor_spec is null, callback is
   * called only locally. This call will block until sst_sent is called
   * from callback.
   *
   * @param wsrep      provider handle
   * @param msg        context message for SST donate callback
   * @param msg_len    length of context message
   * @param donor_spec list of snapshot donors
   */
    wsrep_status_t (*snapshot)(wsrep_t*    wsrep,
                               const void* msg,
                               size_t      msg_len,
                               const char* donor_spec);

  /*!
   * @brief Returns an array fo status variables.
   *        Array is terminated by Null variable name.
   *
   * @param wsrep provider handle
   * @return array of struct wsrep_status_var.
   */
    struct wsrep_stats_var* (*stats_get) (wsrep_t* wsrep);

  /*!
   * @brief Release resources that might be associated with the array.
   *
   * @param wsrep     provider handle.
   * @param var_array array returned by stats_get().
   */
    void (*stats_free) (wsrep_t* wsrep, struct wsrep_stats_var* var_array);

  /*!
   * @brief Reset some stats variables to inital value, provider-dependent.
   *
   * @param wsrep provider handle.
   */
    void (*stats_reset) (wsrep_t* wsrep);

  /*!
   * @brief Pauses writeset applying/committing.
   *
   * @return global sequence number of the paused state or negative error code.
   */
    wsrep_seqno_t (*pause) (wsrep_t* wsrep);

  /*!
   * @brief Resumes writeset applying/committing.
   */
    wsrep_status_t (*resume) (wsrep_t* wsrep);

  /*!
   * @brief Desynchronize from cluster
   *
   * Effectively turns off flow control for this node, allowing it
   * to fall behind the cluster.
   */
    wsrep_status_t (*desync) (wsrep_t* wsrep);

  /*!
   * @brief Request to resynchronize with cluster.
   *
   * Effectively turns on flow control. Asynchronous - actual synchronization
   * event to be deliverred via sync_cb.
   */
    wsrep_status_t (*resync) (wsrep_t* wsrep);

  /*!
   * @brief Acquire global named lock
   *
   * @param wsrep  wsrep provider handle
   * @param name   lock name
   * @param shared shared or exclusive lock
   * @param owner  64-bit owner ID
   * @param tout   timeout in nanoseconds.
   *               0 - return immediately, -1 wait forever.
   * @return          wsrep status or negative error code
   * @retval -EDEADLK lock was already acquired by this thread
   * @retval -EBUSY   lock was busy
   */
    wsrep_status_t (*lock) (wsrep_t* wsrep,
                            const char* name, wsrep_bool_t shared,
                            uint64_t owner, int64_t tout);

  /*!
   * @brief Release global named lock
   *
   * @param wsrep   wsrep provider handle
   * @param name    lock name
   * @param owner   64-bit owner ID
   * @return        wsrep status or negative error code
   * @retval -EPERM lock does not belong to this owner
   */
    wsrep_status_t (*unlock) (wsrep_t* wsrep, const char* name, uint64_t owner);

  /*!
   * @brief Check if global named lock is locked
   *
   * @param wsrep wsrep provider handle
   * @param name  lock name
   * @param owner if not NULL will contain 64-bit owner ID
   * @param node  if not NULL will contain owner's node UUID
   * @return true if lock is locked
   */
    wsrep_bool_t (*is_locked) (wsrep_t* wsrep, const char* name, uint64_t* conn,
                               wsrep_uuid_t* node);

  /*!
   * wsrep provider name
   */
    const char* provider_name;

  /*!
   * wsrep provider version
   */
    const char* provider_version;

  /*!
   * wsrep provider vendor name
   */
    const char* provider_vendor;

  /*!
   * @brief Frees allocated resources before unloading the library.
   * @param wsrep provider handle
   */
    void (*free)(wsrep_t* wsrep);

    void *dlh;    //!< reserved for future use
    void *ctx;    //!< reserved for implemetation private context
};


/*!
 *
 * @brief Loads wsrep library
 *
 * @param spec   path to wsrep library. If NULL or WSREP_NONE initialises dummy
 *               pass-through implementation.
 * @param hptr   wsrep handle
 * @param log_cb callback to handle loader messages. Otherwise writes to stderr.
 *
 * @return zero on success, errno on failure
 */
int wsrep_load(const char* spec, wsrep_t** hptr, wsrep_log_cb_t log_cb);

/*!
 * @brief Unloads wsrep library and frees associated resources
 *
 * @param hptr wsrep handler pointer
 */
void wsrep_unload(wsrep_t* hptr);

#ifdef __cplusplus
}
#endif

#endif /* WSREP_H */