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/*-
* Copyright (c) 2014-2018 MongoDB, Inc.
* Copyright (c) 2008-2014 WiredTiger, Inc.
* All rights reserved.
*
* See the file LICENSE for redistribution information.
*/
#include "wt_internal.h"
#define WT_DHANDLE_CAN_DISCARD(dhandle) \
(!F_ISSET(dhandle, WT_DHANDLE_EXCLUSIVE | WT_DHANDLE_OPEN) && \
(dhandle)->session_inuse == 0 && (dhandle)->session_ref == 0)
/*
* __sweep_mark --
* Mark idle handles with a time of death, and note if we see dead
* handles.
*/
static void
__sweep_mark(WT_SESSION_IMPL *session, time_t now)
{
WT_CONNECTION_IMPL *conn;
WT_DATA_HANDLE *dhandle;
conn = S2C(session);
TAILQ_FOREACH(dhandle, &conn->dhqh, q) {
if (WT_IS_METADATA(dhandle))
continue;
/*
* There are some internal increments of the in-use count such
* as eviction. Don't keep handles alive because of those
* cases, but if we see multiple cursors open, clear the time
* of death.
*/
if (dhandle->session_inuse > 1)
dhandle->timeofdeath = 0;
/*
* If the handle is open exclusive or currently in use, or the
* time of death is already set, move on.
*/
if (F_ISSET(dhandle, WT_DHANDLE_EXCLUSIVE) ||
dhandle->session_inuse > 0 ||
dhandle->timeofdeath != 0)
continue;
dhandle->timeofdeath = now;
WT_STAT_CONN_INCR(session, dh_sweep_tod);
}
}
/*
* __sweep_expire_one --
* Mark a single handle dead.
*/
static int
__sweep_expire_one(WT_SESSION_IMPL *session)
{
WT_BTREE *btree;
WT_DATA_HANDLE *dhandle;
WT_DECL_RET;
dhandle = session->dhandle;
btree = dhandle->type == WT_DHANDLE_TYPE_BTREE ? dhandle->handle : NULL;
/*
* Acquire an exclusive lock on the handle and mark it dead.
*
* The close would require I/O if an update cannot be written
* (updates in a no-longer-referenced file might not yet be
* globally visible if sessions have disjoint sets of files
* open). In that case, skip it: we'll retry the close the
* next time, after the transaction state has progressed.
*
* We don't set WT_DHANDLE_EXCLUSIVE deliberately, we want
* opens to block on us and then retry rather than returning an
* EBUSY error to the application. This is done holding the
* handle list lock so that connection-level handle searches
* never need to retry.
*/
WT_RET(__wt_try_writelock(session, &dhandle->rwlock));
/* Only sweep clean trees where all updates are visible. */
if (btree != NULL && (btree->modified || !__wt_txn_visible_all(session,
btree->rec_max_txn, WT_TIMESTAMP_NULL(&btree->rec_max_timestamp))))
goto err;
/*
* Mark the handle dead and close the underlying handle.
*
* For btree handles, closing the handle decrements the open file
* count, meaning the close loop won't overrun the configured minimum.
*/
ret = __wt_conn_dhandle_close(session, false, true);
err: __wt_writeunlock(session, &dhandle->rwlock);
return (ret);
}
/*
* __sweep_expire --
* Mark trees dead if they are clean and haven't been accessed recently,
* until we have reached the configured minimum number of handles.
*/
static int
__sweep_expire(WT_SESSION_IMPL *session, time_t now)
{
WT_CONNECTION_IMPL *conn;
WT_DATA_HANDLE *dhandle;
WT_DECL_RET;
conn = S2C(session);
TAILQ_FOREACH(dhandle, &conn->dhqh, q) {
/*
* Ignore open files once the btree file count is below the
* minimum number of handles.
*/
if (conn->open_btree_count < conn->sweep_handles_min)
break;
if (WT_IS_METADATA(dhandle) ||
!F_ISSET(dhandle, WT_DHANDLE_OPEN) ||
dhandle->session_inuse != 0 ||
dhandle->timeofdeath == 0 ||
difftime(now, dhandle->timeofdeath) <=
conn->sweep_idle_time)
continue;
/*
* For tables, we need to hold the table lock to avoid racing
* with cursor opens.
*/
if (dhandle->type == WT_DHANDLE_TYPE_TABLE)
WT_WITH_TABLE_WRITE_LOCK(session,
WT_WITH_DHANDLE(session, dhandle,
ret = __sweep_expire_one(session)));
else
WT_WITH_DHANDLE(session, dhandle,
ret = __sweep_expire_one(session));
WT_RET_BUSY_OK(ret);
}
return (0);
}
/*
* __sweep_discard_trees --
* Discard pages from dead trees.
*/
static int
__sweep_discard_trees(WT_SESSION_IMPL *session, u_int *dead_handlesp)
{
WT_CONNECTION_IMPL *conn;
WT_DATA_HANDLE *dhandle;
WT_DECL_RET;
*dead_handlesp = 0;
conn = S2C(session);
TAILQ_FOREACH(dhandle, &conn->dhqh, q) {
if (WT_DHANDLE_CAN_DISCARD(dhandle))
++*dead_handlesp;
if (!F_ISSET(dhandle, WT_DHANDLE_OPEN) ||
!F_ISSET(dhandle, WT_DHANDLE_DEAD))
continue;
/* If the handle is marked dead, flush it from cache. */
WT_WITH_DHANDLE(session, dhandle, ret =
__wt_conn_dhandle_close(session, false, false));
/* We closed the btree handle. */
if (ret == 0) {
WT_STAT_CONN_INCR(session, dh_sweep_close);
++*dead_handlesp;
} else
WT_STAT_CONN_INCR(session, dh_sweep_ref);
WT_RET_BUSY_OK(ret);
}
return (0);
}
/*
* __sweep_remove_one --
* Remove a closed handle from the connection list.
*/
static int
__sweep_remove_one(WT_SESSION_IMPL *session, WT_DATA_HANDLE *dhandle)
{
WT_DECL_RET;
/* Try to get exclusive access. */
WT_RET(__wt_try_writelock(session, &dhandle->rwlock));
/*
* If there are no longer any references to the handle in any
* sessions, attempt to discard it.
*/
if (!WT_DHANDLE_CAN_DISCARD(dhandle))
WT_ERR(EBUSY);
WT_WITH_DHANDLE(session, dhandle,
ret = __wt_conn_dhandle_discard_single(session, false, true));
/*
* If the handle was not successfully discarded, unlock it and
* don't retry the discard until it times out again.
*/
if (ret != 0) {
err: __wt_writeunlock(session, &dhandle->rwlock);
}
return (ret);
}
/*
* __sweep_remove_handles --
* Remove closed handles from the connection list.
*/
static int
__sweep_remove_handles(WT_SESSION_IMPL *session)
{
WT_CONNECTION_IMPL *conn;
WT_DATA_HANDLE *dhandle, *dhandle_tmp;
WT_DECL_RET;
conn = S2C(session);
TAILQ_FOREACH_SAFE(dhandle, &conn->dhqh, q, dhandle_tmp) {
if (WT_IS_METADATA(dhandle))
continue;
if (!WT_DHANDLE_CAN_DISCARD(dhandle))
continue;
if (dhandle->type == WT_DHANDLE_TYPE_TABLE)
WT_WITH_TABLE_WRITE_LOCK(session,
WT_WITH_HANDLE_LIST_WRITE_LOCK(session,
ret = __sweep_remove_one(session, dhandle)));
else
WT_WITH_HANDLE_LIST_WRITE_LOCK(session,
ret = __sweep_remove_one(session, dhandle));
if (ret == 0)
WT_STAT_CONN_INCR(session, dh_sweep_remove);
else
WT_STAT_CONN_INCR(session, dh_sweep_ref);
WT_RET_BUSY_OK(ret);
}
return (ret == EBUSY ? 0 : ret);
}
/*
* __sweep_server_run_chk --
* Check to decide if the sweep server should continue running.
*/
static bool
__sweep_server_run_chk(WT_SESSION_IMPL *session)
{
return (F_ISSET(S2C(session), WT_CONN_SERVER_SWEEP));
}
/*
* __sweep_server --
* The handle sweep server thread.
*/
static WT_THREAD_RET
__sweep_server(void *arg)
{
WT_CONNECTION_IMPL *conn;
WT_DECL_RET;
WT_SESSION_IMPL *session;
time_t last, now;
uint64_t last_las_sweep_id, min_sleep, oldest_id;
u_int dead_handles;
session = arg;
conn = S2C(session);
last_las_sweep_id = WT_TXN_NONE;
min_sleep = WT_MIN(WT_LAS_SWEEP_SEC, conn->sweep_interval);
/*
* Sweep for dead and excess handles.
*/
__wt_seconds(session, &last);
for (;;) {
/* Wait until the next event. */
__wt_cond_wait(session, conn->sweep_cond,
min_sleep * WT_MILLION, __sweep_server_run_chk);
/* Check if we're quitting or being reconfigured. */
if (!__sweep_server_run_chk(session))
break;
__wt_seconds(session, &now);
/*
* Sweep the lookaside table. If the lookaside table hasn't yet
* been written, there's no work to do.
*
* Don't sweep the lookaside table if the cache is stuck full.
* The sweep uses the cache and can exacerbate the problem.
* If we try to sweep when the cache is full or we aren't
* making progress in eviction, sweeping can wind up constantly
* bringing in and evicting pages from the lookaside table,
* which will stop the cache from moving into the stuck state.
*/
if (now - last >= WT_LAS_SWEEP_SEC &&
!__wt_las_empty(session) &&
!__wt_cache_stuck(session)) {
oldest_id = __wt_txn_oldest_id(session);
if (WT_TXNID_LT(last_las_sweep_id, oldest_id)) {
WT_ERR(__wt_las_sweep(session));
last_las_sweep_id = oldest_id;
}
}
/*
* See if it is time to sweep the data handles. Those are swept
* less frequently than the lookaside table by default and the
* frequency is controlled by a user setting.
*/
if ((uint64_t)(now - last) < conn->sweep_interval)
continue;
WT_STAT_CONN_INCR(session, dh_sweeps);
/*
* Mark handles with a time of death, and report whether any
* handles are marked dead. If sweep_idle_time is 0, handles
* never become idle.
*/
if (conn->sweep_idle_time != 0)
__sweep_mark(session, now);
/*
* Close handles if we have reached the configured limit.
* If sweep_idle_time is 0, handles never become idle.
*/
if (conn->sweep_idle_time != 0 &&
conn->open_btree_count >= conn->sweep_handles_min)
WT_ERR(__sweep_expire(session, now));
WT_ERR(__sweep_discard_trees(session, &dead_handles));
if (dead_handles > 0)
WT_ERR(__sweep_remove_handles(session));
}
if (0) {
err: WT_PANIC_MSG(session, ret, "handle sweep server error");
}
return (WT_THREAD_RET_VALUE);
}
/*
* __wt_sweep_config --
* Pull out sweep configuration settings
*/
int
__wt_sweep_config(WT_SESSION_IMPL *session, const char *cfg[])
{
WT_CONFIG_ITEM cval;
WT_CONNECTION_IMPL *conn;
conn = S2C(session);
/*
* A non-zero idle time is incompatible with in-memory, and the default
* is non-zero; set the in-memory configuration idle time to zero.
*/
conn->sweep_idle_time = 0;
WT_RET(__wt_config_gets(session, cfg, "in_memory", &cval));
if (cval.val == 0) {
WT_RET(__wt_config_gets(session,
cfg, "file_manager.close_idle_time", &cval));
conn->sweep_idle_time = (uint64_t)cval.val;
}
WT_RET(__wt_config_gets(session,
cfg, "file_manager.close_scan_interval", &cval));
conn->sweep_interval = (uint64_t)cval.val;
WT_RET(__wt_config_gets(session,
cfg, "file_manager.close_handle_minimum", &cval));
conn->sweep_handles_min = (uint64_t)cval.val;
return (0);
}
/*
* __wt_sweep_create --
* Start the handle sweep thread.
*/
int
__wt_sweep_create(WT_SESSION_IMPL *session)
{
WT_CONNECTION_IMPL *conn;
uint32_t session_flags;
conn = S2C(session);
/* Set first, the thread might run before we finish up. */
F_SET(conn, WT_CONN_SERVER_SWEEP);
/*
* Handle sweep does enough I/O it may be called upon to perform slow
* operations for the block manager. Sweep should not block due to the
* cache being full.
*/
session_flags = WT_SESSION_CAN_WAIT | WT_SESSION_IGNORE_CACHE_SIZE;
WT_RET(__wt_open_internal_session(
conn, "sweep-server", true, session_flags, &conn->sweep_session));
session = conn->sweep_session;
/*
* Sweep should have it's own lookaside cursor to avoid blocking reads
* and eviction when processing drops.
*/
if (F_ISSET(conn, WT_CONN_LOOKASIDE_OPEN))
WT_RET(__wt_las_cursor_open(session));
WT_RET(__wt_cond_alloc(
session, "handle sweep server", &conn->sweep_cond));
WT_RET(__wt_thread_create(
session, &conn->sweep_tid, __sweep_server, session));
conn->sweep_tid_set = 1;
return (0);
}
/*
* __wt_sweep_destroy --
* Destroy the handle-sweep thread.
*/
int
__wt_sweep_destroy(WT_SESSION_IMPL *session)
{
WT_CONNECTION_IMPL *conn;
WT_DECL_RET;
WT_SESSION *wt_session;
conn = S2C(session);
F_CLR(conn, WT_CONN_SERVER_SWEEP);
if (conn->sweep_tid_set) {
__wt_cond_signal(session, conn->sweep_cond);
WT_TRET(__wt_thread_join(session, conn->sweep_tid));
conn->sweep_tid_set = 0;
}
__wt_cond_destroy(session, &conn->sweep_cond);
if (conn->sweep_session != NULL) {
wt_session = &conn->sweep_session->iface;
WT_TRET(wt_session->close(wt_session, NULL));
conn->sweep_session = NULL;
}
return (ret);
}
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