/*
* __wt_async_op_enqueue --
* Enqueue an operation onto the work queue.
*/
int
__wt_async_op_enqueue(WT_SESSION_IMPL *session, WT_ASYNC_OP_IMPL *op)
{
WT_ASYNC *async;
WT_CONNECTION_IMPL *conn;
WT_DECL_RET;
uint64_t cur_head, cur_tail, my_alloc, my_slot;
#ifdef HAVE_DIAGNOSTIC
WT_ASYNC_OP_IMPL *my_op;
#endif
conn = S2C(session);
async = conn->async;
/*
* If an application re-uses a WT_ASYNC_OP, we end up here with an
* invalid object.
*/
if (op->state != WT_ASYNCOP_READY)
WT_RET_MSG(session, EINVAL,
"application error: WT_ASYNC_OP already in use");
/*
* Enqueue op at the tail of the work queue.
* We get our slot in the ring buffer to use.
*/
my_alloc = WT_ATOMIC_ADD8(async->alloc_head, 1);
my_slot = my_alloc % async->async_qsize;
/*
* Make sure we haven't wrapped around the queue.
* If so, wait for the tail to advance off this slot.
*/
WT_ORDERED_READ(cur_tail, async->tail_slot);
while (cur_tail == my_slot) {
__wt_yield();
WT_ORDERED_READ(cur_tail, async->tail_slot);
}
#ifdef HAVE_DIAGNOSTIC
WT_ORDERED_READ(my_op, async->async_queue[my_slot]);
if (my_op != NULL)
return (__wt_panic(session));
#endif
WT_PUBLISH(async->async_queue[my_slot], op);
op->state = WT_ASYNCOP_ENQUEUED;
if (WT_ATOMIC_ADD4(async->cur_queue, 1) > async->max_queue)
WT_PUBLISH(async->max_queue, async->cur_queue);
/*
* Multiple threads may be adding ops to the queue. We need to wait
* our turn to make our slot visible to workers.
*/
WT_ORDERED_READ(cur_head, async->head);
while (cur_head != (my_alloc - 1)) {
__wt_yield();
WT_ORDERED_READ(cur_head, async->head);
}
WT_PUBLISH(async->head, my_alloc);
return (ret);
}
/*
* __wt_txn_get_oldest --
* Update the current transaction's cached copy of the oldest snap_min
* value.
*/
void
__wt_txn_get_oldest(WT_SESSION_IMPL *session)
{
WT_CONNECTION_IMPL *conn;
WT_TXN *txn;
WT_TXN_GLOBAL *txn_global;
WT_TXN_STATE *s;
wt_txnid_t id, oldest_snap_min;
uint32_t i, session_cnt;
conn = S2C(session);
txn = &session->txn;
txn_global = &conn->txn_global;
/* If nothing has changed since last time, we're done. */
if (txn->last_oldest_gen == txn_global->gen)
return;
txn->last_oldest_gen = txn_global->gen;
oldest_snap_min =
(txn->id != WT_TXN_NONE) ? txn->id : txn_global->current;
WT_ORDERED_READ(session_cnt, conn->session_cnt);
for (i = 0, s = txn_global->states;
i < session_cnt;
i++, s++) {
if ((id = s->snap_min) != WT_TXN_NONE &&
TXNID_LT(id, oldest_snap_min))
oldest_snap_min = id;
}
txn->oldest_snap_min = oldest_snap_min;
}
/*
* __wt_txn_get_snapshot --
* Set up a snapshot in the current transaction, without allocating an ID.
*/
void
__wt_txn_get_snapshot(
WT_SESSION_IMPL *session, wt_txnid_t my_id, wt_txnid_t max_id, int force)
{
WT_CONNECTION_IMPL *conn;
WT_TXN *txn;
WT_TXN_GLOBAL *txn_global;
WT_TXN_STATE *s, *txn_state;
wt_txnid_t current_id, id, oldest_snap_min;
uint32_t i, n, session_cnt;
conn = S2C(session);
txn = &session->txn;
txn_global = &conn->txn_global;
txn_state = &txn_global->states[session->id];
/* If nothing has changed since last time, we're done. */
if (!force && txn->last_id == txn_global->current &&
txn->last_gen == txn_global->gen) {
txn_state->snap_min = txn->snap_min;
return;
}
do {
/* Take a copy of the current session ID. */
txn->last_gen = txn->last_oldest_gen = txn_global->gen;
txn->last_id = oldest_snap_min = current_id =
txn_global->current;
/* Copy the array of concurrent transactions. */
WT_ORDERED_READ(session_cnt, conn->session_cnt);
for (i = n = 0, s = txn_global->states;
i < session_cnt;
i++, s++) {
/* Ignore the session's own transaction. */
if (i == session->id)
continue;
if ((id = s->snap_min) != WT_TXN_NONE)
if (TXNID_LT(id, oldest_snap_min))
oldest_snap_min = id;
if ((id = s->id) == WT_TXN_NONE)
continue;
else if (max_id == WT_TXN_NONE || TXNID_LT(id, max_id))
txn->snapshot[n++] = id;
}
/*
* Ensure the snapshot reads are scheduled before re-checking
* the global current ID.
*/
WT_READ_BARRIER();
} while (current_id != txn_global->current);
__txn_sort_snapshot(session, n,
(max_id != WT_TXN_NONE) ? max_id : current_id,
oldest_snap_min);
txn_state->snap_min =
(my_id == WT_TXN_NONE || TXNID_LT(txn->snap_min, my_id)) ?
txn->snap_min : my_id;
}
/*
* __split_oldest_gen --
* Calculate the oldest active split generation.
*/
static uint64_t
__split_oldest_gen(WT_SESSION_IMPL *session)
{
WT_CONNECTION_IMPL *conn;
WT_SESSION_IMPL *s;
uint64_t gen, oldest;
u_int i, session_cnt;
conn = S2C(session);
WT_ORDERED_READ(session_cnt, conn->session_cnt);
for (i = 0, s = conn->sessions, oldest = conn->split_gen + 1;
i < session_cnt;
i++, s++)
if (((gen = s->split_gen) != 0) && gen < oldest)
oldest = gen;
return (oldest);
}
/*
* __wt_txn_update_oldest --
* Sweep the running transactions to update the oldest ID required.
* !!!
* If a data-source is calling the WT_EXTENSION_API.transaction_oldest
* method (for the oldest transaction ID not yet visible to a running
* transaction), and then comparing that oldest ID against committed
* transactions to see if updates for a committed transaction are still
* visible to running transactions, the oldest transaction ID may be
* the same as the last committed transaction ID, if the transaction
* state wasn't refreshed after the last transaction committed. Push
* past the last committed transaction.
*/
void
__wt_txn_update_oldest(WT_SESSION_IMPL *session, int force)
{
WT_CONNECTION_IMPL *conn;
WT_SESSION_IMPL *oldest_session;
WT_TXN_GLOBAL *txn_global;
WT_TXN_STATE *s;
uint64_t current_id, id, last_running, oldest_id, prev_oldest_id;
uint32_t i, session_cnt;
int32_t count;
int last_running_moved;
conn = S2C(session);
txn_global = &conn->txn_global;
current_id = last_running = txn_global->current;
oldest_session = NULL;
prev_oldest_id = txn_global->oldest_id;
/*
* For pure read-only workloads, or if the update isn't forced and the
* oldest ID isn't too far behind, avoid scanning.
*/
if (prev_oldest_id == current_id ||
(!force && WT_TXNID_LT(current_id, prev_oldest_id + 100)))
return;
/*
* We're going to scan. Increment the count of scanners to prevent the
* oldest ID from moving forwards. Spin if the count is negative,
* which indicates that some thread is moving the oldest ID forwards.
*/
do {
if ((count = txn_global->scan_count) < 0)
WT_PAUSE();
} while (count < 0 ||
!WT_ATOMIC_CAS4(txn_global->scan_count, count, count + 1));
/* The oldest ID cannot change until the scan count goes to zero. */
prev_oldest_id = txn_global->oldest_id;
current_id = oldest_id = last_running = txn_global->current;
/* Walk the array of concurrent transactions. */
WT_ORDERED_READ(session_cnt, conn->session_cnt);
for (i = 0, s = txn_global->states; i < session_cnt; i++, s++) {
/*
* Update the oldest ID.
*
* Ignore: IDs older than the oldest ID we saw. This can happen
* if we race with a thread that is allocating an ID -- the ID
* will not be used because the thread will keep spinning until
* it gets a valid one.
*/
if ((id = s->id) != WT_TXN_NONE &&
WT_TXNID_LE(prev_oldest_id, id) &&
WT_TXNID_LT(id, last_running))
last_running = id;
/*
* !!!
* Note: Don't ignore snap_min values older than the previous
* oldest ID. Read-uncommitted operations publish snap_min
* values without incrementing scan_count to protect the global
* table. See the comment in __wt_txn_cursor_op for
* more details.
*/
if ((id = s->snap_min) != WT_TXN_NONE &&
WT_TXNID_LT(id, oldest_id)) {
oldest_id = id;
oldest_session = &conn->sessions[i];
}
}
if (WT_TXNID_LT(last_running, oldest_id))
oldest_id = last_running;
/* The oldest ID can't move past any named snapshots. */
if ((id = txn_global->nsnap_oldest_id) != WT_TXN_NONE &&
WT_TXNID_LT(id, oldest_id))
oldest_id = id;
/* Update the last running ID. */
last_running_moved =
WT_TXNID_LT(txn_global->last_running, last_running);
/* Update the oldest ID. */
if ((WT_TXNID_LT(prev_oldest_id, oldest_id) || last_running_moved) &&
WT_ATOMIC_CAS4(txn_global->scan_count, 1, -1)) {
WT_ORDERED_READ(session_cnt, conn->session_cnt);
for (i = 0, s = txn_global->states; i < session_cnt; i++, s++) {
if ((id = s->id) != WT_TXN_NONE &&
WT_TXNID_LT(id, last_running))
last_running = id;
if ((id = s->snap_min) != WT_TXN_NONE &&
WT_TXNID_LT(id, oldest_id))
oldest_id = id;
}
if (WT_TXNID_LT(last_running, oldest_id))
oldest_id = last_running;
#ifdef HAVE_DIAGNOSTIC
/*
* Make sure the ID doesn't move past any named snapshots.
*
* Don't include the read/assignment in the assert statement.
* Coverity complains if there are assignments only done in
* diagnostic builds, and when the read is from a volatile.
*/
id = txn_global->nsnap_oldest_id;
WT_ASSERT(session,
id == WT_TXN_NONE || !WT_TXNID_LT(id, oldest_id));
#endif
if (WT_TXNID_LT(txn_global->last_running, last_running))
txn_global->last_running = last_running;
if (WT_TXNID_LT(txn_global->oldest_id, oldest_id))
txn_global->oldest_id = oldest_id;
WT_ASSERT(session, txn_global->scan_count == -1);
txn_global->scan_count = 0;
} else {
if (WT_VERBOSE_ISSET(session, WT_VERB_TRANSACTION) &&
current_id - oldest_id > 10000 && last_running_moved &&
oldest_session != NULL) {
(void)__wt_verbose(session, WT_VERB_TRANSACTION,
"old snapshot %" PRIu64
" pinned in session %d [%s]"
" with snap_min %" PRIu64 "\n",
oldest_id, oldest_session->id,
oldest_session->lastop,
oldest_session->txn.snap_min);
}
WT_ASSERT(session, txn_global->scan_count > 0);
(void)WT_ATOMIC_SUB4(txn_global->scan_count, 1);
}
}
/*
* __wt_txn_get_snapshot --
* Allocate a snapshot.
*/
void
__wt_txn_get_snapshot(WT_SESSION_IMPL *session)
{
WT_CONNECTION_IMPL *conn;
WT_TXN *txn;
WT_TXN_GLOBAL *txn_global;
WT_TXN_STATE *s, *txn_state;
uint64_t current_id, id;
uint64_t prev_oldest_id, snap_min;
uint32_t i, n, session_cnt;
int32_t count;
conn = S2C(session);
txn = &session->txn;
txn_global = &conn->txn_global;
txn_state = WT_SESSION_TXN_STATE(session);
/*
* We're going to scan. Increment the count of scanners to prevent the
* oldest ID from moving forwards. Spin if the count is negative,
* which indicates that some thread is moving the oldest ID forwards.
*/
do {
if ((count = txn_global->scan_count) < 0)
WT_PAUSE();
} while (count < 0 ||
!WT_ATOMIC_CAS4(txn_global->scan_count, count, count + 1));
current_id = snap_min = txn_global->current;
prev_oldest_id = txn_global->oldest_id;
/* For pure read-only workloads, avoid scanning. */
if (prev_oldest_id == current_id) {
txn_state->snap_min = current_id;
__txn_sort_snapshot(session, 0, current_id);
/* Check that the oldest ID has not moved in the meantime. */
if (prev_oldest_id == txn_global->oldest_id) {
WT_ASSERT(session, txn_global->scan_count > 0);
(void)WT_ATOMIC_SUB4(txn_global->scan_count, 1);
return;
}
}
/* Walk the array of concurrent transactions. */
WT_ORDERED_READ(session_cnt, conn->session_cnt);
for (i = n = 0, s = txn_global->states; i < session_cnt; i++, s++) {
/*
* Build our snapshot of any concurrent transaction IDs.
*
* Ignore:
* - Our own ID: we always read our own updates.
* - The ID if it is older than the oldest ID we saw. This
* can happen if we race with a thread that is allocating
* an ID -- the ID will not be used because the thread will
* keep spinning until it gets a valid one.
*/
if (s != txn_state &&
(id = s->id) != WT_TXN_NONE &&
WT_TXNID_LE(prev_oldest_id, id)) {
txn->snapshot[n++] = id;
if (WT_TXNID_LT(id, snap_min))
snap_min = id;
}
}
/*
* If we got a new snapshot, update the published snap_min for this
* session.
*/
WT_ASSERT(session, WT_TXNID_LE(prev_oldest_id, snap_min));
WT_ASSERT(session, prev_oldest_id == txn_global->oldest_id);
txn_state->snap_min = snap_min;
WT_ASSERT(session, txn_global->scan_count > 0);
(void)WT_ATOMIC_SUB4(txn_global->scan_count, 1);
__txn_sort_snapshot(session, n, current_id);
}
/*
* __wt_btcur_prev --
* Move to the previous record in the tree.
*/
int
__wt_btcur_prev(WT_CURSOR_BTREE *cbt, int discard)
{
WT_DECL_RET;
WT_PAGE *page;
WT_SESSION_IMPL *session;
uint32_t flags;
int newpage;
session = (WT_SESSION_IMPL *)cbt->iface.session;
WT_DSTAT_INCR(session, cursor_prev);
flags = WT_TREE_SKIP_INTL | WT_TREE_PREV; /* Tree walk flags. */
if (discard)
LF_SET(WT_TREE_DISCARD);
retry: WT_RET(__cursor_func_init(cbt, 0));
__cursor_position_clear(cbt);
/*
* If we aren't already iterating in the right direction, there's
* some setup to do.
*/
if (!F_ISSET(cbt, WT_CBT_ITERATE_PREV))
__wt_btcur_iterate_setup(cbt, 0);
/*
* If this is a modification, we're about to read information from the
* page, save the write generation.
*/
page = cbt->page;
if (discard && page != NULL) {
WT_ERR(__wt_page_modify_init(session, page));
WT_ORDERED_READ(cbt->write_gen, page->modify->write_gen);
}
/*
* Walk any page we're holding until the underlying call returns not-
* found. Then, move to the previous page, until we reach the start
* of the file.
*/
for (newpage = 0;; newpage = 1) {
if (F_ISSET(cbt, WT_CBT_ITERATE_APPEND)) {
switch (page->type) {
case WT_PAGE_COL_FIX:
ret = __cursor_fix_append_prev(cbt, newpage);
break;
case WT_PAGE_COL_VAR:
ret = __cursor_var_append_prev(cbt, newpage);
break;
WT_ILLEGAL_VALUE_ERR(session);
}
if (ret == 0)
break;
F_CLR(cbt, WT_CBT_ITERATE_APPEND);
if (ret != WT_NOTFOUND)
break;
newpage = 1;
}
if (page != NULL) {
switch (page->type) {
case WT_PAGE_COL_FIX:
ret = __cursor_fix_prev(cbt, newpage);
break;
case WT_PAGE_COL_VAR:
ret = __cursor_var_prev(cbt, newpage);
break;
case WT_PAGE_ROW_LEAF:
ret = __cursor_row_prev(cbt, newpage);
break;
WT_ILLEGAL_VALUE_ERR(session);
}
if (ret != WT_NOTFOUND)
break;
}
cbt->page = NULL;
WT_ERR(__wt_tree_walk(session, &page, flags));
WT_ERR_TEST(page == NULL, WT_NOTFOUND);
WT_ASSERT(session,
page->type != WT_PAGE_COL_INT &&
page->type != WT_PAGE_ROW_INT);
cbt->page = page;
/* Initialize the page's modification information */
if (discard) {
WT_ERR(__wt_page_modify_init(session, page));
WT_ORDERED_READ(
cbt->write_gen, page->modify->write_gen);
}
/*
* The last page in a column-store has appended entries.
* We handle it separately from the usual cursor code:
* it's only that one page and it's in a simple format.
*/
if (page->type != WT_PAGE_ROW_LEAF &&
(cbt->ins_head = WT_COL_APPEND(page)) != NULL)
F_SET(cbt, WT_CBT_ITERATE_APPEND);
}
err: if (ret == WT_RESTART)
goto retry;
WT_TRET(__cursor_func_resolve(cbt, ret));
return (ret);
}
/*
* __txn_oldest_scan --
* Sweep the running transactions to calculate the oldest ID required.
*/
static void
__txn_oldest_scan(WT_SESSION_IMPL *session,
uint64_t *oldest_idp, uint64_t *last_runningp,
WT_SESSION_IMPL **oldest_sessionp)
{
WT_CONNECTION_IMPL *conn;
WT_SESSION_IMPL *oldest_session;
WT_TXN_GLOBAL *txn_global;
WT_TXN_STATE *s;
uint64_t id, last_running, oldest_id, prev_oldest_id;
uint32_t i, session_cnt;
conn = S2C(session);
txn_global = &conn->txn_global;
oldest_session = NULL;
/* The oldest ID cannot change while we are holding the scan lock. */
prev_oldest_id = txn_global->oldest_id;
oldest_id = last_running = txn_global->current;
/* Walk the array of concurrent transactions. */
WT_ORDERED_READ(session_cnt, conn->session_cnt);
for (i = 0, s = txn_global->states; i < session_cnt; i++, s++) {
/*
* Update the oldest ID.
*
* Ignore: IDs older than the oldest ID we saw. This can happen
* if we race with a thread that is allocating an ID -- the ID
* will not be used because the thread will keep spinning until
* it gets a valid one.
*/
if ((id = s->id) != WT_TXN_NONE &&
WT_TXNID_LE(prev_oldest_id, id) &&
WT_TXNID_LT(id, last_running))
last_running = id;
/*
* !!!
* Note: Don't ignore snap_min values older than the previous
* oldest ID. Read-uncommitted operations publish snap_min
* values without acquiring the scan lock to protect the global
* table. See the comment in __wt_txn_cursor_op for
* more details.
*/
if ((id = s->snap_min) != WT_TXN_NONE &&
WT_TXNID_LT(id, oldest_id)) {
oldest_id = id;
oldest_session = &conn->sessions[i];
}
}
if (WT_TXNID_LT(last_running, oldest_id))
oldest_id = last_running;
/* The oldest ID can't move past any named snapshots. */
if ((id = txn_global->nsnap_oldest_id) != WT_TXN_NONE &&
WT_TXNID_LT(id, oldest_id))
oldest_id = id;
*oldest_idp = oldest_id;
*oldest_sessionp = oldest_session;
*last_runningp = last_running;
}
/*
* __wt_txn_get_snapshot --
* Allocate a snapshot.
*/
int
__wt_txn_get_snapshot(WT_SESSION_IMPL *session)
{
WT_CONNECTION_IMPL *conn;
WT_DECL_RET;
WT_TXN *txn;
WT_TXN_GLOBAL *txn_global;
WT_TXN_STATE *s, *txn_state;
uint64_t current_id, id;
uint64_t prev_oldest_id, snap_min;
uint32_t i, n, session_cnt;
conn = S2C(session);
txn = &session->txn;
txn_global = &conn->txn_global;
txn_state = WT_SESSION_TXN_STATE(session);
n = 0;
/*
* Spin waiting for the lock: the sleeps in our blocking readlock
* implementation are too slow for scanning the transaction table.
*/
while ((ret =
__wt_try_readlock(session, txn_global->scan_rwlock)) == EBUSY)
WT_PAUSE();
WT_RET(ret);
current_id = snap_min = txn_global->current;
prev_oldest_id = txn_global->oldest_id;
/*
* Include the checkpoint transaction, if one is running: we should
* ignore any uncommitted changes the checkpoint has written to the
* metadata. We don't have to keep the checkpoint's changes pinned so
* don't including it in the published snap_min.
*/
if ((id = txn_global->checkpoint_txnid) != WT_TXN_NONE)
txn->snapshot[n++] = id;
/* For pure read-only workloads, avoid scanning. */
if (prev_oldest_id == current_id) {
txn_state->snap_min = current_id;
/* Check that the oldest ID has not moved in the meantime. */
WT_ASSERT(session, prev_oldest_id == txn_global->oldest_id);
goto done;
}
/* Walk the array of concurrent transactions. */
WT_ORDERED_READ(session_cnt, conn->session_cnt);
for (i = 0, s = txn_global->states; i < session_cnt; i++, s++) {
/*
* Build our snapshot of any concurrent transaction IDs.
*
* Ignore:
* - Our own ID: we always read our own updates.
* - The ID if it is older than the oldest ID we saw. This
* can happen if we race with a thread that is allocating
* an ID -- the ID will not be used because the thread will
* keep spinning until it gets a valid one.
*/
if (s != txn_state &&
(id = s->id) != WT_TXN_NONE &&
WT_TXNID_LE(prev_oldest_id, id)) {
txn->snapshot[n++] = id;
if (WT_TXNID_LT(id, snap_min))
snap_min = id;
}
}
/*
* If we got a new snapshot, update the published snap_min for this
* session.
*/
WT_ASSERT(session, WT_TXNID_LE(prev_oldest_id, snap_min));
WT_ASSERT(session, prev_oldest_id == txn_global->oldest_id);
txn_state->snap_min = snap_min;
done: __wt_readunlock(session, txn_global->scan_rwlock);
__txn_sort_snapshot(session, n, current_id);
return (0);
}
/*
* __wt_txn_refresh --
* Allocate a transaction ID and/or a snapshot.
*/
void
__wt_txn_refresh(WT_SESSION_IMPL *session, uint64_t max_id, int get_snapshot)
{
WT_CONNECTION_IMPL *conn;
WT_TXN *txn;
WT_TXN_GLOBAL *txn_global;
WT_TXN_STATE *s, *txn_state;
uint64_t current_id, id, snap_min, oldest_id, prev_oldest_id;
uint32_t i, n, session_cnt;
int32_t count;
conn = S2C(session);
txn = &session->txn;
txn_global = &conn->txn_global;
txn_state = &txn_global->states[session->id];
prev_oldest_id = txn_global->oldest_id;
current_id = snap_min = txn_global->current;
/* For pure read-only workloads, avoid updates to shared state. */
if (!get_snapshot) {
/*
* If we are trying to update the oldest ID and it is already
* equal to the current ID, there is no point scanning.
*/
if (prev_oldest_id == current_id)
return;
} else if (txn->id == max_id &&
txn->snapshot_count == 0 &&
txn->snap_min == snap_min &&
TXNID_LE(prev_oldest_id, snap_min)) {
txn_state->snap_min = txn->snap_min;
/* If nothing has changed in the meantime, we're done. */
if (txn_global->scan_count == 0 &&
txn_global->oldest_id == prev_oldest_id)
return;
}
/*
* We're going to scan. Increment the count of scanners to prevent the
* oldest ID from moving forwards. Spin if the count is negative,
* which indicates that some thread is moving the oldest ID forwards.
*/
do {
if ((count = txn_global->scan_count) < 0)
WT_PAUSE();
} while (count < 0 ||
!WT_ATOMIC_CAS(txn_global->scan_count, count, count + 1));
/* The oldest ID cannot change until the scan count goes to zero. */
prev_oldest_id = txn_global->oldest_id;
current_id = snap_min = txn_global->current;
/* If the maximum ID is constrained, so is the oldest. */
oldest_id = (max_id != WT_TXN_NONE) ? max_id : snap_min;
/* Walk the array of concurrent transactions. */
WT_ORDERED_READ(session_cnt, conn->session_cnt);
for (i = n = 0, s = txn_global->states; i < session_cnt; i++, s++) {
/*
* Ignore the ID if we are committing (indicated by max_id
* being set): it is about to be released.
*
* Also ignore the ID if it is older than the oldest ID we saw.
* This can happen if we race with a thread that is allocating
* an ID -- the ID will not be used because the thread will
* keep spinning until it gets a valid one.
*/
if ((id = s->id) != WT_TXN_NONE && id + 1 != max_id &&
TXNID_LE(prev_oldest_id, id)) {
if (get_snapshot)
txn->snapshot[n++] = id;
if (TXNID_LT(id, snap_min))
snap_min = id;
}
/*
* Ignore the session's own snap_min if we are in the process
* of updating it.
*/
if (get_snapshot && s == txn_state)
continue;
/*
* !!!
* Note: Don't ignore snap_min values older than the previous
* oldest ID. Read-uncommitted operations publish snap_min
* values without incrementing scan_count to protect the global
* table. See the comment in __wt_txn_cursor_op for
* more details.
*/
if ((id = s->snap_min) != WT_TXN_NONE &&
TXNID_LT(id, oldest_id))
oldest_id = id;
}
if (TXNID_LT(snap_min, oldest_id))
oldest_id = snap_min;
if (get_snapshot) {
WT_ASSERT(session, TXNID_LE(prev_oldest_id, snap_min));
WT_ASSERT(session, prev_oldest_id == txn_global->oldest_id);
txn_state->snap_min = snap_min;
}
/*
* Update the last running ID if we have a much newer value or we are
* forcing an update.
*/
if (!get_snapshot || snap_min > txn_global->last_running + 100)
txn_global->last_running = snap_min;
/*
* Update the oldest ID if we have a newer ID and we can get exclusive
* access. During normal snapshot refresh, only do this if we have a
* much newer value. Once we get exclusive access, do another pass to
* make sure nobody else is using an earlier ID.
*/
if (max_id == WT_TXN_NONE &&
TXNID_LT(prev_oldest_id, oldest_id) &&
(!get_snapshot || oldest_id - prev_oldest_id > 100) &&
WT_ATOMIC_CAS(txn_global->scan_count, 1, -1)) {
WT_ORDERED_READ(session_cnt, conn->session_cnt);
for (i = 0, s = txn_global->states; i < session_cnt; i++, s++) {
if ((id = s->id) != WT_TXN_NONE &&
TXNID_LT(id, oldest_id))
oldest_id = id;
if ((id = s->snap_min) != WT_TXN_NONE &&
TXNID_LT(id, oldest_id))
oldest_id = id;
}
if (TXNID_LT(txn_global->oldest_id, oldest_id))
txn_global->oldest_id = oldest_id;
txn_global->scan_count = 0;
} else {
WT_ASSERT(session, txn_global->scan_count > 0);
(void)WT_ATOMIC_SUB(txn_global->scan_count, 1);
}
if (get_snapshot)
__txn_sort_snapshot(session, n, current_id);
}
/*
* __txn_oldest_scan --
* Sweep the running transactions to calculate the oldest ID required.
*/
static void
__txn_oldest_scan(WT_SESSION_IMPL *session,
uint64_t *oldest_idp, uint64_t *last_runningp, uint64_t *metadata_pinnedp,
WT_SESSION_IMPL **oldest_sessionp)
{
WT_CONNECTION_IMPL *conn;
WT_SESSION_IMPL *oldest_session;
WT_TXN_GLOBAL *txn_global;
WT_TXN_STATE *s;
uint64_t id, last_running, metadata_pinned, oldest_id, prev_oldest_id;
uint32_t i, session_cnt;
conn = S2C(session);
txn_global = &conn->txn_global;
oldest_session = NULL;
/* The oldest ID cannot change while we are holding the scan lock. */
prev_oldest_id = txn_global->oldest_id;
last_running = oldest_id = txn_global->current;
if ((metadata_pinned = txn_global->checkpoint_state.id) == WT_TXN_NONE)
metadata_pinned = oldest_id;
/* Walk the array of concurrent transactions. */
WT_ORDERED_READ(session_cnt, conn->session_cnt);
for (i = 0, s = txn_global->states; i < session_cnt; i++, s++) {
/* Update the last running transaction ID. */
if ((id = s->id) != WT_TXN_NONE &&
WT_TXNID_LE(prev_oldest_id, id) &&
WT_TXNID_LT(id, last_running))
last_running = id;
/* Update the metadata pinned ID. */
if ((id = s->metadata_pinned) != WT_TXN_NONE &&
WT_TXNID_LT(id, metadata_pinned))
metadata_pinned = id;
/*
* !!!
* Note: Don't ignore pinned ID values older than the previous
* oldest ID. Read-uncommitted operations publish pinned ID
* values without acquiring the scan lock to protect the global
* table. See the comment in __wt_txn_cursor_op for more
* details.
*/
if ((id = s->pinned_id) != WT_TXN_NONE &&
WT_TXNID_LT(id, oldest_id)) {
oldest_id = id;
oldest_session = &conn->sessions[i];
}
}
if (WT_TXNID_LT(last_running, oldest_id))
oldest_id = last_running;
/* The oldest ID can't move past any named snapshots. */
if ((id = txn_global->nsnap_oldest_id) != WT_TXN_NONE &&
WT_TXNID_LT(id, oldest_id))
oldest_id = id;
/* The metadata pinned ID can't move past the oldest ID. */
if (WT_TXNID_LT(oldest_id, metadata_pinned))
metadata_pinned = oldest_id;
*last_runningp = last_running;
*metadata_pinnedp = metadata_pinned;
*oldest_idp = oldest_id;
*oldest_sessionp = oldest_session;
}
/*
* __wt_verbose_dump_txn --
* Output diagnostic information about the global transaction state.
*/
int
__wt_verbose_dump_txn(WT_SESSION_IMPL *session)
{
WT_CONNECTION_IMPL *conn;
WT_SESSION_IMPL *sess;
WT_TXN_GLOBAL *txn_global;
WT_TXN_STATE *s;
uint64_t id;
uint32_t i, session_cnt;
#ifdef HAVE_TIMESTAMPS
char hex_timestamp[3][2 * WT_TIMESTAMP_SIZE + 1];
#endif
conn = S2C(session);
txn_global = &conn->txn_global;
WT_RET(__wt_msg(session, "%s", WT_DIVIDER));
WT_RET(__wt_msg(session, "transaction state dump"));
WT_RET(__wt_msg(session, "current ID: %" PRIu64, txn_global->current));
WT_RET(__wt_msg(session,
"last running ID: %" PRIu64, txn_global->last_running));
WT_RET(__wt_msg(session, "oldest ID: %" PRIu64, txn_global->oldest_id));
#ifdef HAVE_TIMESTAMPS
WT_RET(__wt_timestamp_to_hex_string(
session, hex_timestamp[0], &txn_global->commit_timestamp));
WT_RET(__wt_msg(session, "commit timestamp: %s", hex_timestamp[0]));
WT_RET(__wt_timestamp_to_hex_string(
session, hex_timestamp[0], &txn_global->oldest_timestamp));
WT_RET(__wt_msg(session, "oldest timestamp: %s", hex_timestamp[0]));
WT_RET(__wt_timestamp_to_hex_string(
session, hex_timestamp[0], &txn_global->pinned_timestamp));
WT_RET(__wt_msg(session, "pinned timestamp: %s", hex_timestamp[0]));
WT_RET(__wt_timestamp_to_hex_string(
session, hex_timestamp[0], &txn_global->stable_timestamp));
WT_RET(__wt_msg(session, "stable timestamp: %s", hex_timestamp[0]));
WT_RET(__wt_msg(session, "has_commit_timestamp: %s",
txn_global->has_commit_timestamp ? "yes" : "no"));
WT_RET(__wt_msg(session, "has_oldest_timestamp: %s",
txn_global->has_oldest_timestamp ? "yes" : "no"));
WT_RET(__wt_msg(session, "has_pinned_timestamp: %s",
txn_global->has_pinned_timestamp ? "yes" : "no"));
WT_RET(__wt_msg(session, "has_stable_timestamp: %s",
txn_global->has_stable_timestamp ? "yes" : "no"));
WT_RET(__wt_msg(session, "oldest_is_pinned: %s",
txn_global->oldest_is_pinned ? "yes" : "no"));
WT_RET(__wt_msg(session, "stable_is_pinned: %s",
txn_global->stable_is_pinned ? "yes" : "no"));
#endif
WT_RET(__wt_msg(session, "checkpoint running: %s",
txn_global->checkpoint_running ? "yes" : "no"));
WT_RET(__wt_msg(session, "checkpoint generation: %" PRIu64,
__wt_gen(session, WT_GEN_CHECKPOINT)));
WT_RET(__wt_msg(session, "checkpoint pinned ID: %" PRIu64,
txn_global->checkpoint_state.pinned_id));
WT_RET(__wt_msg(session, "checkpoint txn ID: %" PRIu64,
txn_global->checkpoint_state.id));
WT_RET(__wt_msg(session,
"oldest named snapshot ID: %" PRIu64, txn_global->nsnap_oldest_id));
WT_ORDERED_READ(session_cnt, conn->session_cnt);
WT_RET(__wt_msg(session, "session count: %" PRIu32, session_cnt));
WT_RET(__wt_msg(session, "Transaction state of active sessions:"));
/*
* Walk each session transaction state and dump information. Accessing
* the content of session handles is not thread safe, so some
* information may change while traversing if other threads are active
* at the same time, which is OK since this is diagnostic code.
*/
for (i = 0, s = txn_global->states; i < session_cnt; i++, s++) {
/* Skip sessions with no active transaction */
if ((id = s->id) == WT_TXN_NONE && s->pinned_id == WT_TXN_NONE)
continue;
sess = &conn->sessions[i];
WT_RET(__wt_msg(session,
"ID: %" PRIu64
", pinned ID: %" PRIu64
", metadata pinned ID: %" PRIu64
", name: %s",
id, s->pinned_id, s->metadata_pinned,
sess->name == NULL ?
"EMPTY" : sess->name));
WT_RET(__wt_verbose_dump_txn_one(sess, &sess->txn));
}
return (0);
}
/*
* __wt_txn_begin --
* Begin a transaction.
*/
int
__wt_txn_begin(WT_SESSION_IMPL *session, const char *cfg[])
{
WT_CONFIG_ITEM cval;
WT_CONNECTION_IMPL *conn;
WT_TXN *txn;
WT_TXN_GLOBAL *txn_global;
WT_TXN_STATE *s, *txn_state;
wt_txnid_t id, oldest_snap_min;
uint32_t i, n, session_cnt;
conn = S2C(session);
txn = &session->txn;
txn_global = &conn->txn_global;
txn_state = &txn_global->states[session->id];
WT_ASSERT(session, txn_state->id == WT_TXN_NONE);
WT_RET(__wt_config_gets_defno(session, cfg, "isolation", &cval));
if (cval.len == 0)
txn->isolation = session->isolation;
else
txn->isolation =
WT_STRING_MATCH("snapshot", cval.str, cval.len) ?
TXN_ISO_SNAPSHOT :
WT_STRING_MATCH("read-committed", cval.str, cval.len) ?
TXN_ISO_READ_COMMITTED : TXN_ISO_READ_UNCOMMITTED;
F_SET(txn, TXN_RUNNING);
do {
/*
* Allocate a transaction ID.
*
* We use an atomic increment to ensure that we get a unique
* ID, then publish that to the global state table.
*
* If two threads race to allocate an ID, only the latest ID
* will proceed. The winning thread can be sure its snapshot
* contains all of the earlier active IDs. Threads that race
* and get an earlier ID may not appear in the snapshot,
* but they will loop and allocate a new ID before proceeding
* to make any updates.
*
* This potentially wastes transaction IDs when threads race to
* begin transactions, but that is the price we pay to keep
* this path latch free.
*/
do {
txn->id = WT_ATOMIC_ADD(txn_global->current, 1);
} while (txn->id == WT_TXN_NONE || txn->id == WT_TXN_ABORTED);
WT_PUBLISH(txn_state->id, txn->id);
/*
* If we are starting a snapshot isolation transaction, get
* a snapshot of the running transactions.
*
* If we already have a snapshot (e.g., for an auto-commit
* operation), update it so that the newly-allocated ID is
* visible.
*/
if (txn->isolation == TXN_ISO_SNAPSHOT) {
txn->last_gen = txn->last_oldest_gen = txn_global->gen;
oldest_snap_min = txn->id;
/* Copy the array of concurrent transactions. */
WT_ORDERED_READ(session_cnt, conn->session_cnt);
for (i = n = 0, s = txn_global->states;
i < session_cnt;
i++, s++) {
if ((id = s->snap_min) != WT_TXN_NONE)
if (TXNID_LT(id, oldest_snap_min))
oldest_snap_min = id;
if ((id = s->id) == WT_TXN_NONE)
continue;
else
txn->snapshot[n++] = id;
}
__txn_sort_snapshot(
session, n, txn->id, oldest_snap_min);
txn_state->snap_min = txn->snap_min;
}
/*
* Ensure the snapshot reads are complete before re-checking
* the global current ID.
*/
WT_READ_BARRIER();
} while (txn->id != txn_global->current);
return (0);
}
