Just move, no code changes otherwise.

Part of MDEV-7974 - backport fix for mysql bug#12161 (XA and binlog)

1 files changed, 797 insertions, 0 deletions

diff --git a/sql/xa.cc b/sql/xa.cc
new file mode 100644
index 00000000000..4de6b101e38
--- /dev/null
+++ b/sql/xa.cc
@@ -0,0 +1,797 @@
+/*
+   Copyright (c) 2000, 2016, Oracle and/or its affiliates.
+   Copyright (c) 2009, 2019, MariaDB Corporation.
+
+   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
+*/
+
+#include "mariadb.h"
+#include "sql_class.h"
+#include "transaction.h"
+
+
+/***************************************************************************
+  Handling of XA id cacheing
+***************************************************************************/
+class XID_cache_element
+{
+  /*
+    m_state is used to prevent elements from being deleted while XA RECOVER
+    iterates xid cache and to prevent recovered elments from being acquired by
+    multiple threads.
+
+    bits 1..29 are reference counter
+    bit 30 is RECOVERED flag
+    bit 31 is ACQUIRED flag (thread owns this xid)
+    bit 32 is unused
+
+    Newly allocated and deleted elements have m_state set to 0.
+
+    On lock() m_state is atomically incremented. It also creates load-ACQUIRE
+    memory barrier to make sure m_state is actually updated before furhter
+    memory accesses. Attempting to lock an element that has neither ACQUIRED
+    nor RECOVERED flag set returns failure and further accesses to element
+    memory are forbidden.
+
+    On unlock() m_state is decremented. It also creates store-RELEASE memory
+    barrier to make sure m_state is actually updated after preceding memory
+    accesses.
+
+    ACQUIRED flag is set when thread registers it's xid or when thread acquires
+    recovered xid.
+
+    RECOVERED flag is set for elements found during crash recovery.
+
+    ACQUIRED and RECOVERED flags are cleared before element is deleted from
+    hash in a spin loop, after last reference is released.
+  */
+  std::atomic<int32_t> m_state;
+public:
+  static const int32 ACQUIRED= 1 << 30;
+  static const int32 RECOVERED= 1 << 29;
+  XID_STATE *m_xid_state;
+  bool is_set(int32_t flag)
+  { return m_state.load(std::memory_order_relaxed) & flag; }
+  void set(int32_t flag)
+  {
+    DBUG_ASSERT(!is_set(ACQUIRED | RECOVERED));
+    m_state.fetch_add(flag, std::memory_order_relaxed);
+  }
+  bool lock()
+  {
+    int32_t old= m_state.fetch_add(1, std::memory_order_acquire);
+    if (old & (ACQUIRED | RECOVERED))
+      return true;
+    unlock();
+    return false;
+  }
+  void unlock()
+  { m_state.fetch_sub(1, std::memory_order_release); }
+  void mark_uninitialized()
+  {
+    int32_t old= ACQUIRED;
+    while (!m_state.compare_exchange_weak(old, 0,
+                                          std::memory_order_relaxed,
+                                          std::memory_order_relaxed))
+    {
+      old&= ACQUIRED | RECOVERED;
+      (void) LF_BACKOFF();
+    }
+  }
+  bool acquire_recovered()
+  {
+    int32_t old= RECOVERED;
+    while (!m_state.compare_exchange_weak(old, ACQUIRED | RECOVERED,
+                                          std::memory_order_relaxed,
+                                          std::memory_order_relaxed))
+    {
+      if (!(old & RECOVERED) || (old & ACQUIRED))
+        return false;
+      old= RECOVERED;
+      (void) LF_BACKOFF();
+    }
+    return true;
+  }
+  static void lf_hash_initializer(LF_HASH *hash __attribute__((unused)),
+                                  XID_cache_element *element,
+                                  XID_STATE *xid_state)
+  {
+    DBUG_ASSERT(!element->is_set(ACQUIRED | RECOVERED));
+    element->m_xid_state= xid_state;
+    xid_state->xid_cache_element= element;
+  }
+  static void lf_alloc_constructor(uchar *ptr)
+  {
+    XID_cache_element *element= (XID_cache_element*) (ptr + LF_HASH_OVERHEAD);
+    element->m_state= 0;
+  }
+  static void lf_alloc_destructor(uchar *ptr)
+  {
+    XID_cache_element *element= (XID_cache_element*) (ptr + LF_HASH_OVERHEAD);
+    DBUG_ASSERT(!element->is_set(ACQUIRED));
+    if (element->is_set(RECOVERED))
+      my_free(element->m_xid_state);
+  }
+  static uchar *key(const XID_cache_element *element, size_t *length,
+                    my_bool not_used __attribute__((unused)))
+  {
+    *length= element->m_xid_state->xid.key_length();
+    return element->m_xid_state->xid.key();
+  }
+};
+
+
+static LF_HASH xid_cache;
+static bool xid_cache_inited;
+const char *xa_state_names[]= {
+  "NON-EXISTING", "ACTIVE", "IDLE", "PREPARED", "ROLLBACK ONLY"
+};
+
+
+bool THD::fix_xid_hash_pins()
+{
+  if (!xid_hash_pins)
+    xid_hash_pins= lf_hash_get_pins(&xid_cache);
+  return !xid_hash_pins;
+}
+
+
+void xid_cache_init()
+{
+  xid_cache_inited= true;
+  lf_hash_init(&xid_cache, sizeof(XID_cache_element), LF_HASH_UNIQUE, 0, 0,
+               (my_hash_get_key) XID_cache_element::key, &my_charset_bin);
+  xid_cache.alloc.constructor= XID_cache_element::lf_alloc_constructor;
+  xid_cache.alloc.destructor= XID_cache_element::lf_alloc_destructor;
+  xid_cache.initializer=
+    (lf_hash_initializer) XID_cache_element::lf_hash_initializer;
+}
+
+
+void xid_cache_free()
+{
+  if (xid_cache_inited)
+  {
+    lf_hash_destroy(&xid_cache);
+    xid_cache_inited= false;
+  }
+}
+
+
+/**
+  Find recovered XA transaction by XID.
+*/
+
+static XID_STATE *xid_cache_search(THD *thd, XID *xid)
+{
+  XID_STATE *xs= 0;
+  DBUG_ASSERT(thd->xid_hash_pins);
+  XID_cache_element *element=
+    (XID_cache_element*) lf_hash_search(&xid_cache, thd->xid_hash_pins,
+                                        xid->key(), xid->key_length());
+  if (element)
+  {
+    if (element->acquire_recovered())
+      xs= element->m_xid_state;
+    lf_hash_search_unpin(thd->xid_hash_pins);
+    DEBUG_SYNC(thd, "xa_after_search");
+  }
+  return xs;
+}
+
+
+bool xid_cache_insert(XID *xid, enum xa_states xa_state)
+{
+  XID_STATE *xs;
+  LF_PINS *pins;
+  int res= 1;
+
+  if (!(pins= lf_hash_get_pins(&xid_cache)))
+    return true;
+
+  if ((xs= (XID_STATE*) my_malloc(sizeof(*xs), MYF(MY_WME))))
+  {
+    xs->xa_state=xa_state;
+    xs->xid.set(xid);
+    xs->rm_error=0;
+
+    if ((res= lf_hash_insert(&xid_cache, pins, xs)))
+      my_free(xs);
+    else
+      xs->xid_cache_element->set(XID_cache_element::RECOVERED);
+    if (res == 1)
+      res= 0;
+  }
+  lf_hash_put_pins(pins);
+  return res;
+}
+
+
+bool xid_cache_insert(THD *thd, XID_STATE *xid_state)
+{
+  if (thd->fix_xid_hash_pins())
+    return true;
+
+  int res= lf_hash_insert(&xid_cache, thd->xid_hash_pins, xid_state);
+  switch (res)
+  {
+  case 0:
+    xid_state->xid_cache_element->set(XID_cache_element::ACQUIRED);
+    break;
+  case 1:
+    my_error(ER_XAER_DUPID, MYF(0));
+    /* fall through */
+  default:
+    xid_state->xid_cache_element= 0;
+  }
+  return res;
+}
+
+
+void xid_cache_delete(THD *thd, XID_STATE *xid_state)
+{
+  if (xid_state->xid_cache_element)
+  {
+    bool recovered= xid_state->xid_cache_element->is_set(XID_cache_element::RECOVERED);
+    DBUG_ASSERT(thd->xid_hash_pins);
+    xid_state->xid_cache_element->mark_uninitialized();
+    lf_hash_delete(&xid_cache, thd->xid_hash_pins,
+                   xid_state->xid.key(), xid_state->xid.key_length());
+    xid_state->xid_cache_element= 0;
+    if (recovered)
+      my_free(xid_state);
+  }
+}
+
+
+struct xid_cache_iterate_arg
+{
+  my_hash_walk_action action;
+  void *argument;
+};
+
+static my_bool xid_cache_iterate_callback(XID_cache_element *element,
+                                          xid_cache_iterate_arg *arg)
+{
+  my_bool res= FALSE;
+  if (element->lock())
+  {
+    res= arg->action(element->m_xid_state, arg->argument);
+    element->unlock();
+  }
+  return res;
+}
+
+static int xid_cache_iterate(THD *thd, my_hash_walk_action action, void *arg)
+{
+  xid_cache_iterate_arg argument= { action, arg };
+  return thd->fix_xid_hash_pins() ? -1 :
+         lf_hash_iterate(&xid_cache, thd->xid_hash_pins,
+                         (my_hash_walk_action) xid_cache_iterate_callback,
+                         &argument);
+}
+
+
+/**
+  Mark a XA transaction as rollback-only if the RM unilaterally
+  rolled back the transaction branch.
+
+  @note If a rollback was requested by the RM, this function sets
+        the appropriate rollback error code and transits the state
+        to XA_ROLLBACK_ONLY.
+
+  @return TRUE if transaction was rolled back or if the transaction
+          state is XA_ROLLBACK_ONLY. FALSE otherwise.
+*/
+static bool xa_trans_rolled_back(XID_STATE *xid_state)
+{
+  if (xid_state->rm_error)
+  {
+    switch (xid_state->rm_error) {
+    case ER_LOCK_WAIT_TIMEOUT:
+      my_error(ER_XA_RBTIMEOUT, MYF(0));
+      break;
+    case ER_LOCK_DEADLOCK:
+      my_error(ER_XA_RBDEADLOCK, MYF(0));
+      break;
+    default:
+      my_error(ER_XA_RBROLLBACK, MYF(0));
+    }
+    xid_state->xa_state= XA_ROLLBACK_ONLY;
+  }
+
+  return (xid_state->xa_state == XA_ROLLBACK_ONLY);
+}
+
+
+/**
+  Rollback the active XA transaction.
+
+  @note Resets rm_error before calling ha_rollback(), so
+        the thd->transaction.xid structure gets reset
+        by ha_rollback() / THD::transaction::cleanup().
+
+  @return TRUE if the rollback failed, FALSE otherwise.
+*/
+
+static bool xa_trans_force_rollback(THD *thd)
+{
+  /*
+    We must reset rm_error before calling ha_rollback(),
+    so thd->transaction.xid structure gets reset
+    by ha_rollback()/THD::transaction::cleanup().
+  */
+  thd->transaction.xid_state.rm_error= 0;
+  if (ha_rollback_trans(thd, true))
+  {
+    my_error(ER_XAER_RMERR, MYF(0));
+    return true;
+  }
+  return false;
+}
+
+
+/**
+  Starts an XA transaction with the given xid value.
+
+  @param thd    Current thread
+
+  @retval FALSE  Success
+  @retval TRUE   Failure
+*/
+
+bool trans_xa_start(THD *thd)
+{
+  enum xa_states xa_state= thd->transaction.xid_state.xa_state;
+  DBUG_ENTER("trans_xa_start");
+
+  if (xa_state == XA_IDLE && thd->lex->xa_opt == XA_RESUME)
+  {
+    bool not_equal= !thd->transaction.xid_state.xid.eq(thd->lex->xid);
+    if (not_equal)
+      my_error(ER_XAER_NOTA, MYF(0));
+    else
+      thd->transaction.xid_state.xa_state= XA_ACTIVE;
+    DBUG_RETURN(not_equal);
+  }
+
+  /* TODO: JOIN is not supported yet. */
+  if (thd->lex->xa_opt != XA_NONE)
+    my_error(ER_XAER_INVAL, MYF(0));
+  else if (xa_state != XA_NOTR)
+    my_error(ER_XAER_RMFAIL, MYF(0), xa_state_names[xa_state]);
+  else if (thd->locked_tables_mode || thd->in_active_multi_stmt_transaction())
+    my_error(ER_XAER_OUTSIDE, MYF(0));
+  else if (!trans_begin(thd))
+  {
+    DBUG_ASSERT(thd->transaction.xid_state.xid.is_null());
+    thd->transaction.xid_state.xa_state= XA_ACTIVE;
+    thd->transaction.xid_state.rm_error= 0;
+    thd->transaction.xid_state.xid.set(thd->lex->xid);
+    if (xid_cache_insert(thd, &thd->transaction.xid_state))
+    {
+      thd->transaction.xid_state.xa_state= XA_NOTR;
+      thd->transaction.xid_state.xid.null();
+      trans_rollback(thd);
+      DBUG_RETURN(true);
+    }
+    DBUG_RETURN(FALSE);
+  }
+
+  DBUG_RETURN(TRUE);
+}
+
+
+/**
+  Put a XA transaction in the IDLE state.
+
+  @param thd    Current thread
+
+  @retval FALSE  Success
+  @retval TRUE   Failure
+*/
+
+bool trans_xa_end(THD *thd)
+{
+  DBUG_ENTER("trans_xa_end");
+
+  /* TODO: SUSPEND and FOR MIGRATE are not supported yet. */
+  if (thd->lex->xa_opt != XA_NONE)
+    my_error(ER_XAER_INVAL, MYF(0));
+  else if (thd->transaction.xid_state.xa_state != XA_ACTIVE)
+    my_error(ER_XAER_RMFAIL, MYF(0),
+             xa_state_names[thd->transaction.xid_state.xa_state]);
+  else if (!thd->transaction.xid_state.xid.eq(thd->lex->xid))
+    my_error(ER_XAER_NOTA, MYF(0));
+  else if (!xa_trans_rolled_back(&thd->transaction.xid_state))
+    thd->transaction.xid_state.xa_state= XA_IDLE;
+
+  DBUG_RETURN(thd->is_error() ||
+              thd->transaction.xid_state.xa_state != XA_IDLE);
+}
+
+
+/**
+  Put a XA transaction in the PREPARED state.
+
+  @param thd    Current thread
+
+  @retval FALSE  Success
+  @retval TRUE   Failure
+*/
+
+bool trans_xa_prepare(THD *thd)
+{
+  DBUG_ENTER("trans_xa_prepare");
+
+  if (thd->transaction.xid_state.xa_state != XA_IDLE)
+    my_error(ER_XAER_RMFAIL, MYF(0),
+             xa_state_names[thd->transaction.xid_state.xa_state]);
+  else if (!thd->transaction.xid_state.xid.eq(thd->lex->xid))
+    my_error(ER_XAER_NOTA, MYF(0));
+  else if (ha_prepare(thd))
+  {
+    xid_cache_delete(thd, &thd->transaction.xid_state);
+    thd->transaction.xid_state.xa_state= XA_NOTR;
+    my_error(ER_XA_RBROLLBACK, MYF(0));
+  }
+  else
+    thd->transaction.xid_state.xa_state= XA_PREPARED;
+
+  DBUG_RETURN(thd->is_error() ||
+              thd->transaction.xid_state.xa_state != XA_PREPARED);
+}
+
+
+/**
+  Commit and terminate the a XA transaction.
+
+  @param thd    Current thread
+
+  @retval FALSE  Success
+  @retval TRUE   Failure
+*/
+
+bool trans_xa_commit(THD *thd)
+{
+  bool res= TRUE;
+  enum xa_states xa_state= thd->transaction.xid_state.xa_state;
+  DBUG_ENTER("trans_xa_commit");
+
+  if (!thd->transaction.xid_state.xid.eq(thd->lex->xid))
+  {
+    if (thd->fix_xid_hash_pins())
+    {
+      my_error(ER_OUT_OF_RESOURCES, MYF(0));
+      DBUG_RETURN(TRUE);
+    }
+
+    XID_STATE *xs= xid_cache_search(thd, thd->lex->xid);
+    res= !xs;
+    if (res)
+      my_error(ER_XAER_NOTA, MYF(0));
+    else
+    {
+      res= xa_trans_rolled_back(xs);
+      ha_commit_or_rollback_by_xid(thd->lex->xid, !res);
+      xid_cache_delete(thd, xs);
+    }
+    DBUG_RETURN(res);
+  }
+
+  if (xa_trans_rolled_back(&thd->transaction.xid_state))
+  {
+    xa_trans_force_rollback(thd);
+    res= thd->is_error();
+  }
+  else if (xa_state == XA_IDLE && thd->lex->xa_opt == XA_ONE_PHASE)
+  {
+    int r= ha_commit_trans(thd, TRUE);
+    if ((res= MY_TEST(r)))
+      my_error(r == 1 ? ER_XA_RBROLLBACK : ER_XAER_RMERR, MYF(0));
+  }
+  else if (xa_state == XA_PREPARED && thd->lex->xa_opt == XA_NONE)
+  {
+    MDL_request mdl_request;
+
+    /*
+      Acquire metadata lock which will ensure that COMMIT is blocked
+      by active FLUSH TABLES WITH READ LOCK (and vice versa COMMIT in
+      progress blocks FTWRL).
+
+      We allow FLUSHer to COMMIT; we assume FLUSHer knows what it does.
+    */
+    mdl_request.init(MDL_key::BACKUP, "", "", MDL_BACKUP_COMMIT,
+                     MDL_TRANSACTION);
+
+    if (thd->mdl_context.acquire_lock(&mdl_request,
+                                      thd->variables.lock_wait_timeout))
+    {
+      ha_rollback_trans(thd, TRUE);
+      my_error(ER_XAER_RMERR, MYF(0));
+    }
+    else
+    {
+      DEBUG_SYNC(thd, "trans_xa_commit_after_acquire_commit_lock");
+
+      res= MY_TEST(ha_commit_one_phase(thd, 1));
+      if (res)
+        my_error(ER_XAER_RMERR, MYF(0));
+    }
+  }
+  else
+  {
+    my_error(ER_XAER_RMFAIL, MYF(0), xa_state_names[xa_state]);
+    DBUG_RETURN(TRUE);
+  }
+
+  thd->variables.option_bits&= ~(OPTION_BEGIN | OPTION_KEEP_LOG);
+  thd->transaction.all.reset();
+  thd->server_status&=
+    ~(SERVER_STATUS_IN_TRANS | SERVER_STATUS_IN_TRANS_READONLY);
+  DBUG_PRINT("info", ("clearing SERVER_STATUS_IN_TRANS"));
+  xid_cache_delete(thd, &thd->transaction.xid_state);
+  thd->transaction.xid_state.xa_state= XA_NOTR;
+
+  trans_track_end_trx(thd);
+
+  DBUG_RETURN(res);
+}
+
+
+/**
+  Roll back and terminate a XA transaction.
+
+  @param thd    Current thread
+
+  @retval FALSE  Success
+  @retval TRUE   Failure
+*/
+
+bool trans_xa_rollback(THD *thd)
+{
+  bool res= TRUE;
+  enum xa_states xa_state= thd->transaction.xid_state.xa_state;
+  DBUG_ENTER("trans_xa_rollback");
+
+  if (!thd->transaction.xid_state.xid.eq(thd->lex->xid))
+  {
+    if (thd->fix_xid_hash_pins())
+    {
+      my_error(ER_OUT_OF_RESOURCES, MYF(0));
+      DBUG_RETURN(TRUE);
+    }
+
+    XID_STATE *xs= xid_cache_search(thd, thd->lex->xid);
+    if (!xs)
+      my_error(ER_XAER_NOTA, MYF(0));
+    else
+    {
+      xa_trans_rolled_back(xs);
+      ha_commit_or_rollback_by_xid(thd->lex->xid, 0);
+      xid_cache_delete(thd, xs);
+    }
+    DBUG_RETURN(thd->get_stmt_da()->is_error());
+  }
+
+  if (xa_state != XA_IDLE && xa_state != XA_PREPARED && xa_state != XA_ROLLBACK_ONLY)
+  {
+    my_error(ER_XAER_RMFAIL, MYF(0), xa_state_names[xa_state]);
+    DBUG_RETURN(TRUE);
+  }
+
+  res= xa_trans_force_rollback(thd);
+
+  thd->variables.option_bits&= ~(OPTION_BEGIN | OPTION_KEEP_LOG);
+  thd->transaction.all.reset();
+  thd->server_status&=
+    ~(SERVER_STATUS_IN_TRANS | SERVER_STATUS_IN_TRANS_READONLY);
+  DBUG_PRINT("info", ("clearing SERVER_STATUS_IN_TRANS"));
+  xid_cache_delete(thd, &thd->transaction.xid_state);
+  thd->transaction.xid_state.xa_state= XA_NOTR;
+
+  trans_track_end_trx(thd);
+
+  DBUG_RETURN(res);
+}
+
+
+/**
+  return the XID as it appears in the SQL function's arguments.
+  So this string can be passed to XA START, XA PREPARE etc...
+
+  @note
+    the 'buf' has to have space for at least SQL_XIDSIZE bytes.
+*/
+
+
+/*
+  'a'..'z' 'A'..'Z', '0'..'9'
+  and '-' '_' ' ' symbols don't have to be
+  converted.
+*/
+
+static const char xid_needs_conv[128]=
+{
+  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+  0,1,1,1,1,1,1,1,1,1,1,1,1,0,1,1,
+  0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,
+  1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+  0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,0,
+  1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+  0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,1
+};
+
+/*
+  The size of XID string representation in the form
+  'gtrid', 'bqual', formatID
+  see xid_t::get_sql_string() for details.
+*/
+#define SQL_XIDSIZE (XIDDATASIZE * 2 + 8 + MY_INT64_NUM_DECIMAL_DIGITS)
+
+/* The 'buf' has to have space for at least SQL_XIDSIZE bytes. */
+static uint get_sql_xid(XID *xid, char *buf)
+{
+  int tot_len= xid->gtrid_length + xid->bqual_length;
+  int i;
+  const char *orig_buf= buf;
+
+  for (i=0; i<tot_len; i++)
+  {
+    uchar c= ((uchar *) xid->data)[i];
+    if (c >= 128 || xid_needs_conv[c])
+      break;
+  }
+
+  if (i >= tot_len)
+  {
+    /* No need to convert characters to hexadecimals. */
+    *buf++= '\'';
+    memcpy(buf, xid->data, xid->gtrid_length);
+    buf+= xid->gtrid_length;
+    *buf++= '\'';
+    if (xid->bqual_length > 0 || xid->formatID != 1)
+    {
+      *buf++= ',';
+      *buf++= '\'';
+      memcpy(buf, xid->data+xid->gtrid_length, xid->bqual_length);
+      buf+= xid->bqual_length;
+      *buf++= '\'';
+    }
+  }
+  else
+  {
+    *buf++= 'X';
+    *buf++= '\'';
+    for (i= 0; i < xid->gtrid_length; i++)
+    {
+      *buf++=_dig_vec_lower[((uchar*) xid->data)[i] >> 4];
+      *buf++=_dig_vec_lower[((uchar*) xid->data)[i] & 0x0f];
+    }
+    *buf++= '\'';
+    if (xid->bqual_length > 0 || xid->formatID != 1)
+    {
+      *buf++= ',';
+      *buf++= 'X';
+      *buf++= '\'';
+      for (; i < tot_len; i++)
+      {
+        *buf++=_dig_vec_lower[((uchar*) xid->data)[i] >> 4];
+        *buf++=_dig_vec_lower[((uchar*) xid->data)[i] & 0x0f];
+      }
+      *buf++= '\'';
+    }
+  }
+
+  if (xid->formatID != 1)
+  {
+    *buf++= ',';
+    buf+= my_longlong10_to_str_8bit(&my_charset_bin, buf,
+            MY_INT64_NUM_DECIMAL_DIGITS, -10, xid->formatID);
+  }
+
+  return (uint)(buf - orig_buf);
+}
+
+
+/**
+  return the list of XID's to a client, the same way SHOW commands do.
+
+  @note
+    I didn't find in XA specs that an RM cannot return the same XID twice,
+    so mysql_xa_recover does not filter XID's to ensure uniqueness.
+    It can be easily fixed later, if necessary.
+*/
+
+static my_bool xa_recover_callback(XID_STATE *xs, Protocol *protocol,
+                  char *data, uint data_len, CHARSET_INFO *data_cs)
+{
+  if (xs->xa_state == XA_PREPARED)
+  {
+    protocol->prepare_for_resend();
+    protocol->store_longlong((longlong) xs->xid.formatID, FALSE);
+    protocol->store_longlong((longlong) xs->xid.gtrid_length, FALSE);
+    protocol->store_longlong((longlong) xs->xid.bqual_length, FALSE);
+    protocol->store(data, data_len, data_cs);
+    if (protocol->write())
+      return TRUE;
+  }
+  return FALSE;
+}
+
+
+static my_bool xa_recover_callback_short(XID_STATE *xs, Protocol *protocol)
+{
+  return xa_recover_callback(xs, protocol, xs->xid.data,
+      xs->xid.gtrid_length + xs->xid.bqual_length, &my_charset_bin);
+}
+
+
+static my_bool xa_recover_callback_verbose(XID_STATE *xs, Protocol *protocol)
+{
+  char buf[SQL_XIDSIZE];
+  uint len= get_sql_xid(&xs->xid, buf);
+  return xa_recover_callback(xs, protocol, buf, len,
+                             &my_charset_utf8_general_ci);
+}
+
+
+bool mysql_xa_recover(THD *thd)
+{
+  List<Item> field_list;
+  Protocol *protocol= thd->protocol;
+  MEM_ROOT *mem_root= thd->mem_root;
+  my_hash_walk_action action;
+  DBUG_ENTER("mysql_xa_recover");
+
+  field_list.push_back(new (mem_root)
+                       Item_int(thd, "formatID", 0,
+                                MY_INT32_NUM_DECIMAL_DIGITS), mem_root);
+  field_list.push_back(new (mem_root)
+                       Item_int(thd, "gtrid_length", 0,
+                                MY_INT32_NUM_DECIMAL_DIGITS), mem_root);
+  field_list.push_back(new (mem_root)
+                       Item_int(thd, "bqual_length", 0,
+                                MY_INT32_NUM_DECIMAL_DIGITS), mem_root);
+  {
+    uint len;
+    CHARSET_INFO *cs;
+
+    if (thd->lex->verbose)
+    {
+      len= SQL_XIDSIZE;
+      cs= &my_charset_utf8_general_ci;
+      action= (my_hash_walk_action) xa_recover_callback_verbose;
+    }
+    else
+    {
+      len= XIDDATASIZE;
+      cs= &my_charset_bin;
+      action= (my_hash_walk_action) xa_recover_callback_short;
+    }
+
+    field_list.push_back(new (mem_root)
+                         Item_empty_string(thd, "data", len, cs), mem_root);
+  }
+
+  if (protocol->send_result_set_metadata(&field_list,
+                            Protocol::SEND_NUM_ROWS | Protocol::SEND_EOF))
+    DBUG_RETURN(1);
+
+  if (xid_cache_iterate(thd, action, protocol))
+    DBUG_RETURN(1);
+  my_eof(thd);
+  DBUG_RETURN(0);
+}