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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"
static int __evict_page_clean_update(WT_SESSION_IMPL *, WT_REF *, bool);
static int __evict_page_dirty_update(WT_SESSION_IMPL *, WT_REF *, bool);
static int __evict_review(WT_SESSION_IMPL *, WT_REF *, bool, bool *);
/*
* __evict_exclusive_clear --
* Release exclusive access to a page.
*/
static inline void
__evict_exclusive_clear(
WT_SESSION_IMPL *session, WT_REF *ref, uint32_t previous_state)
{
WT_ASSERT(session, ref->state == WT_REF_LOCKED && ref->page != NULL);
WT_REF_SET_STATE(ref, previous_state);
}
/*
* __evict_exclusive --
* Acquire exclusive access to a page.
*/
static inline int
__evict_exclusive(WT_SESSION_IMPL *session, WT_REF *ref)
{
WT_ASSERT(session, ref->state == WT_REF_LOCKED);
/*
* Check for a hazard pointer indicating another thread is using the
* page, meaning the page cannot be evicted.
*/
if (__wt_hazard_check(session, ref) == NULL)
return (0);
WT_STAT_DATA_INCR(session, cache_eviction_hazard);
WT_STAT_CONN_INCR(session, cache_eviction_hazard);
return (__wt_set_return(session, EBUSY));
}
/*
* __wt_page_release_evict --
* Release a reference to a page, and attempt to immediately evict it.
*/
int
__wt_page_release_evict(WT_SESSION_IMPL *session, WT_REF *ref)
{
WT_BTREE *btree;
WT_DECL_RET;
WT_PAGE *page;
uint64_t time_start, time_stop;
uint32_t previous_state;
bool locked, too_big;
btree = S2BT(session);
locked = false;
page = ref->page;
time_start = __wt_clock(session);
/*
* This function always releases the hazard pointer - ensure that's
* done regardless of whether we can get exclusive access. Take some
* care with order of operations: if we release the hazard pointer
* without first locking the page, it could be evicted in between.
*/
previous_state = ref->state;
if ((previous_state == WT_REF_MEM || previous_state == WT_REF_LIMBO) &&
__wt_atomic_casv32(&ref->state, previous_state, WT_REF_LOCKED))
locked = true;
if ((ret = __wt_hazard_clear(session, ref)) != 0 || !locked) {
if (locked)
WT_REF_SET_STATE(ref, previous_state);
return (ret == 0 ? EBUSY : ret);
}
(void)__wt_atomic_addv32(&btree->evict_busy, 1);
too_big = page->memory_footprint >= btree->splitmempage;
/*
* Track how long the call to evict took. If eviction is successful then
* we have one of two pairs of stats to increment.
*/
ret = __wt_evict(session, ref, false, previous_state);
time_stop = __wt_clock(session);
if (ret == 0) {
if (too_big) {
WT_STAT_CONN_INCR(session, cache_eviction_force);
WT_STAT_CONN_INCRV(session, cache_eviction_force_time,
WT_CLOCKDIFF_US(time_stop, time_start));
} else {
/*
* If the page isn't too big, we are evicting it because
* it had a chain of deleted entries that make traversal
* expensive.
*/
WT_STAT_CONN_INCR(session, cache_eviction_force_delete);
WT_STAT_CONN_INCRV(session,
cache_eviction_force_delete_time,
WT_CLOCKDIFF_US(time_stop, time_start));
}
} else {
WT_STAT_CONN_INCR(session, cache_eviction_force_fail);
WT_STAT_CONN_INCRV(session, cache_eviction_force_fail_time,
WT_CLOCKDIFF_US(time_stop, time_start));
}
(void)__wt_atomic_subv32(&btree->evict_busy, 1);
return (ret);
}
/*
* __wt_evict --
* Evict a page.
*/
int
__wt_evict(WT_SESSION_IMPL *session,
WT_REF *ref, bool closing, uint32_t previous_state)
{
WT_CONNECTION_IMPL *conn;
WT_DECL_RET;
WT_PAGE *page;
bool clean_page, inmem_split, local_gen, tree_dead;
conn = S2C(session);
page = ref->page;
local_gen = false;
__wt_verbose(session, WT_VERB_EVICT,
"page %p (%s)", (void *)page, __wt_page_type_string(page->type));
/*
* Enter the eviction generation. If we re-enter eviction, leave the
* previous eviction generation (which must be as low as the current
* generation), untouched.
*/
if (__wt_session_gen(session, WT_GEN_EVICT) == 0) {
local_gen = true;
__wt_session_gen_enter(session, WT_GEN_EVICT);
}
/*
* Get exclusive access to the page if our caller doesn't have the tree
* locked down.
*/
if (!closing) {
WT_ERR(__evict_exclusive(session, ref));
/*
* Now the page is locked, remove it from the LRU eviction
* queue. We have to do this before freeing the page memory or
* otherwise touching the reference because eviction paths
* assume a non-NULL reference on the queue is pointing at
* valid memory.
*/
__wt_evict_list_clear_page(session, ref);
}
/*
* Review the page for conditions that would block its eviction. If the
* check fails (for example, we find a page with active children), quit.
* Make this check for clean pages, too: while unlikely eviction would
* choose an internal page with children, it's not disallowed.
*/
WT_ERR(__evict_review(session, ref, closing, &inmem_split));
/*
* If there was an in-memory split, the tree has been left in the state
* we want: there is nothing more to do.
*/
if (inmem_split)
goto done;
/* Count evictions of internal pages during normal operation. */
if (!closing && WT_PAGE_IS_INTERNAL(page)) {
WT_STAT_CONN_INCR(session, cache_eviction_internal);
WT_STAT_DATA_INCR(session, cache_eviction_internal);
}
/*
* Track the largest page size seen at eviction, it tells us something
* about our ability to force pages out before they're larger than the
* cache.
*/
if (page->memory_footprint > conn->cache->evict_max_page_size)
conn->cache->evict_max_page_size = page->memory_footprint;
/* Figure out whether reconciliation was done on the page */
clean_page = __wt_page_evict_clean(page);
/*
* Discard all page-deleted information. If a truncate call deleted this
* page, there's memory associated with it we no longer need, eviction
* will have built a new version of the page.
*/
if (ref->page_del != NULL) {
__wt_free(session, ref->page_del->update_list);
__wt_free(session, ref->page_del);
}
/* Update the reference and discard the page. */
tree_dead = F_ISSET(session->dhandle, WT_DHANDLE_DEAD);
if (__wt_ref_is_root(ref))
__wt_ref_out(session, ref);
else if ((clean_page && !F_ISSET(conn, WT_CONN_IN_MEMORY)) || tree_dead)
/*
* Pages that belong to dead trees never write back to disk
* and can't support page splits.
*/
WT_ERR(__evict_page_clean_update(
session, ref, tree_dead || closing));
else
WT_ERR(__evict_page_dirty_update(session, ref, closing));
if (clean_page) {
WT_STAT_CONN_INCR(session, cache_eviction_clean);
WT_STAT_DATA_INCR(session, cache_eviction_clean);
} else {
WT_STAT_CONN_INCR(session, cache_eviction_dirty);
WT_STAT_DATA_INCR(session, cache_eviction_dirty);
}
if (0) {
err: if (!closing)
__evict_exclusive_clear(session, ref, previous_state);
WT_STAT_CONN_INCR(session, cache_eviction_fail);
WT_STAT_DATA_INCR(session, cache_eviction_fail);
}
done: /* Leave any local eviction generation. */
if (local_gen)
__wt_session_gen_leave(session, WT_GEN_EVICT);
return (ret);
}
/*
* __evict_delete_ref --
* Mark a page reference deleted and check if the parent can reverse
* split.
*/
static int
__evict_delete_ref(WT_SESSION_IMPL *session, WT_REF *ref, bool closing)
{
WT_DECL_RET;
WT_PAGE *parent;
WT_PAGE_INDEX *pindex;
uint32_t ndeleted;
if (__wt_ref_is_root(ref))
return (0);
/*
* Avoid doing reverse splits when closing the file, it is wasted work
* and some structures may have already been freed.
*/
if (!closing) {
parent = ref->home;
WT_INTL_INDEX_GET(session, parent, pindex);
ndeleted = __wt_atomic_addv32(&pindex->deleted_entries, 1);
/*
* If more than 10% of the parent references are deleted, try a
* reverse split. Don't bother if there is a single deleted
* reference: the internal page is empty and we have to wait
* for eviction to notice.
*
* This will consume the deleted ref (and eventually free it).
* If the reverse split can't get the access it needs because
* something is busy, be sure that the page still ends up
* marked deleted.
*/
if (ndeleted > pindex->entries / 10 && pindex->entries > 1) {
if ((ret = __wt_split_reverse(session, ref)) == 0)
return (0);
WT_RET_BUSY_OK(ret);
/*
* The child must be locked after a failed reverse
* split.
*/
WT_ASSERT(session, ref->state == WT_REF_LOCKED);
}
}
WT_REF_SET_STATE(ref, WT_REF_DELETED);
return (0);
}
/*
* __evict_page_clean_update --
* Update a clean page's reference on eviction.
*/
static int
__evict_page_clean_update(WT_SESSION_IMPL *session, WT_REF *ref, bool closing)
{
WT_DECL_RET;
/*
* Before discarding a page, assert that all updates are globally
* visible unless the tree is closing, dead, or we're evicting with
* history in lookaside.
*/
WT_ASSERT(session,
closing || ref->page->modify == NULL ||
F_ISSET(session->dhandle, WT_DHANDLE_DEAD) ||
(ref->page_las != NULL && ref->page_las->eviction_to_lookaside) ||
__wt_txn_visible_all(session, ref->page->modify->rec_max_txn,
ref->page->modify->rec_max_timestamp));
/*
* Discard the page and update the reference structure. If evicting a
* WT_REF_LIMBO page with active history, transition back to
* WT_REF_LOOKASIDE. Otherwise, a page with a disk address is an
* on-disk page, and a page without a disk address is a re-instantiated
* deleted page (for example, by searching), that was never
* subsequently written.
*/
__wt_ref_out(session, ref);
if (!closing && ref->page_las != NULL &&
ref->page_las->eviction_to_lookaside &&
__wt_page_las_active(session, ref)) {
ref->page_las->eviction_to_lookaside = false;
WT_REF_SET_STATE(ref, WT_REF_LOOKASIDE);
} else if (ref->addr == NULL) {
WT_WITH_PAGE_INDEX(session,
ret = __evict_delete_ref(session, ref, closing));
WT_RET_BUSY_OK(ret);
} else
WT_REF_SET_STATE(ref, WT_REF_DISK);
return (0);
}
/*
* __evict_page_dirty_update --
* Update a dirty page's reference on eviction.
*/
static int
__evict_page_dirty_update(WT_SESSION_IMPL *session, WT_REF *ref, bool closing)
{
WT_ADDR *addr;
WT_DECL_RET;
WT_MULTI multi;
WT_PAGE_MODIFY *mod;
mod = ref->page->modify;
WT_ASSERT(session, ref->addr == NULL);
switch (mod->rec_result) {
case WT_PM_REC_EMPTY: /* Page is empty */
/*
* Update the parent to reference a deleted page. Reconciliation
* left the page "empty", so there's no older transaction in the
* system that might need to see an earlier version of the page.
* There's no backing address, if we're forced to "read" into
* that namespace, we instantiate a new page instead of trying
* to read from the backing store.
*/
__wt_ref_out(session, ref);
WT_WITH_PAGE_INDEX(session,
ret = __evict_delete_ref(session, ref, closing));
WT_RET_BUSY_OK(ret);
break;
case WT_PM_REC_MULTIBLOCK: /* Multiple blocks */
/*
* Either a split where we reconciled a page and it turned into
* a lot of pages or an in-memory page that got too large, we
* forcibly evicted it, and there wasn't anything to write.
*
* The latter is a special case of forced eviction. Imagine a
* thread updating a small set keys on a leaf page. The page
* is too large or has too many deleted items, so we try and
* evict it, but after reconciliation there's only a small
* amount of live data (so it's a single page we can't split),
* and if there's an older reader somewhere, there's data on
* the page we can't write (so the page can't be evicted). In
* that case, we end up here with a single block that we can't
* write. Take advantage of the fact we have exclusive access
* to the page and rewrite it in memory.
*/
if (mod->mod_multi_entries == 1) {
WT_ASSERT(session, closing == false);
WT_RET(__wt_split_rewrite(
session, ref, &mod->mod_multi[0]));
} else
WT_RET(__wt_split_multi(session, ref, closing));
break;
case WT_PM_REC_REPLACE: /* 1-for-1 page swap */
/*
* Update the parent to reference the replacement page.
*
* A page evicted with lookaside entries may not have an
* address, if no updates were visible to reconciliation.
*
* Publish: a barrier to ensure the structure fields are set
* before the state change makes the page available to readers.
*/
if (mod->mod_replace.addr != NULL) {
WT_RET(__wt_calloc_one(session, &addr));
*addr = mod->mod_replace;
mod->mod_replace.addr = NULL;
mod->mod_replace.size = 0;
ref->addr = addr;
}
/*
* Eviction wants to keep this page if we have a disk image,
* re-instantiate the page in memory, else discard the page.
*/
__wt_free(session, ref->page_las);
if (mod->mod_disk_image == NULL) {
if (mod->mod_page_las.las_pageid != 0) {
WT_RET(
__wt_calloc_one(session, &ref->page_las));
*ref->page_las = mod->mod_page_las;
__wt_page_modify_clear(session, ref->page);
__wt_ref_out(session, ref);
WT_REF_SET_STATE(ref, WT_REF_LOOKASIDE);
} else {
__wt_ref_out(session, ref);
WT_REF_SET_STATE(ref, WT_REF_DISK);
}
} else {
/*
* The split code works with WT_MULTI structures, build
* one for the disk image.
*/
memset(&multi, 0, sizeof(multi));
multi.disk_image = mod->mod_disk_image;
WT_RET(__wt_split_rewrite(session, ref, &multi));
}
break;
WT_ILLEGAL_VALUE(session, mod->rec_result);
}
return (0);
}
/*
* __evict_child_check --
* Review an internal page for active children.
*/
static int
__evict_child_check(WT_SESSION_IMPL *session, WT_REF *parent)
{
WT_REF *child;
bool active;
WT_INTL_FOREACH_BEGIN(session, parent->page, child) {
switch (child->state) {
case WT_REF_DISK: /* On-disk */
break;
case WT_REF_DELETED: /* Deleted */
/*
* If the child page was part of a truncate,
* transaction rollback might switch this page into its
* previous state at any time, so the delete must be
* resolved before the parent can be evicted.
*
* We have the internal page locked, which prevents a
* search from descending into it. However, a walk
* from an adjacent leaf page could attempt to hazard
* couple into a child page and free the page_del
* structure as we are examining it. Flip the state to
* locked to make this check safe: if that fails, we
* have raced with a read and should give up on
* evicting the parent.
*/
if (!__wt_atomic_casv32(
&child->state, WT_REF_DELETED, WT_REF_LOCKED))
return (__wt_set_return(session, EBUSY));
active = __wt_page_del_active(session, child, true);
child->state = WT_REF_DELETED;
if (active)
return (__wt_set_return(session, EBUSY));
break;
case WT_REF_LOOKASIDE:
/*
* If the lookaside history is obsolete, the reference
* can be ignored.
*/
if (__wt_page_las_active(session, child))
return (__wt_set_return(session, EBUSY));
break;
default:
return (__wt_set_return(session, EBUSY));
}
} WT_INTL_FOREACH_END;
return (0);
}
/*
* __evict_review --
* Get exclusive access to the page and review the page and its subtree
* for conditions that would block its eviction.
*/
static int
__evict_review(
WT_SESSION_IMPL *session, WT_REF *ref, bool closing, bool *inmem_splitp)
{
WT_CACHE *cache;
WT_CONNECTION_IMPL *conn;
WT_DECL_RET;
WT_PAGE *page;
uint32_t flags;
bool lookaside_retry, *lookaside_retryp, modified;
*inmem_splitp = false;
conn = S2C(session);
page = ref->page;
flags = WT_REC_EVICT;
if (!WT_SESSION_BTREE_SYNC(session))
LF_SET(WT_REC_VISIBLE_ALL);
/*
* Fail if an internal has active children, the children must be evicted
* first. The test is necessary but shouldn't fire much: the eviction
* code is biased for leaf pages, an internal page shouldn't be selected
* for eviction until all children have been evicted.
*/
if (WT_PAGE_IS_INTERNAL(page)) {
WT_WITH_PAGE_INDEX(session,
ret = __evict_child_check(session, ref));
WT_RET(ret);
}
/*
* It is always OK to evict pages from dead trees if they don't have
* children.
*/
if (F_ISSET(session->dhandle, WT_DHANDLE_DEAD))
return (0);
/*
* Retrieve the modified state of the page. This must happen after the
* check for evictable internal pages otherwise there is a race where a
* page could be marked modified due to a child being transitioned to
* WT_REF_DISK after the modified check and before we visited the ref
* while walking the parent index.
*/
modified = __wt_page_is_modified(page);
/*
* Clean pages can't be evicted when running in memory only. This
* should be uncommon - we don't add clean pages to the queue.
*/
if (F_ISSET(conn, WT_CONN_IN_MEMORY) && !modified && !closing)
return (__wt_set_return(session, EBUSY));
/* Check if the page can be evicted. */
if (!closing) {
/*
* Update the oldest ID to avoid wasted effort should it have
* fallen behind current.
*/
if (modified)
WT_RET(__wt_txn_update_oldest(
session, WT_TXN_OLDEST_STRICT));
if (!__wt_page_can_evict(session, ref, inmem_splitp))
return (__wt_set_return(session, EBUSY));
/*
* Check for an append-only workload needing an in-memory split;
* we can't do this earlier because in-memory splits require
* exclusive access. If an in-memory split completes, the page
* stays in memory and the tree is left in the desired state:
* avoid the usual cleanup.
*/
if (*inmem_splitp)
return (__wt_split_insert(session, ref));
}
/* If the page is clean, we're done and we can evict. */
if (!modified)
return (0);
/*
* If reconciliation is disabled for this thread (e.g., during an
* eviction that writes to lookaside), give up.
*/
if (F_ISSET(session, WT_SESSION_NO_RECONCILE))
return (__wt_set_return(session, EBUSY));
/*
* If the page is dirty, reconcile it to decide if we can evict it.
*
* If we have an exclusive lock (we're discarding the tree), assert
* there are no updates we cannot read.
*
* Don't set any other flags for internal pages: there are no update
* lists to be saved and restored, changes can't be written into the
* lookaside table, nor can we re-create internal pages in memory.
*
* For leaf pages:
*
* In-memory pages are a known configuration.
*
* Set the update/restore flag, so reconciliation will write blocks it
* can write and create a list of skipped updates for blocks it cannot
* write, along with disk images. This is how eviction of active, huge
* pages works: we take a big page and reconcile it into blocks, some of
* which we write and discard, the rest of which we re-create as smaller
* in-memory pages, (restoring the updates that stopped us from writing
* the block), and inserting the whole mess into the page's parent. Set
* the flag in all cases because the incremental cost of update/restore
* in reconciliation is minimal, eviction shouldn't have picked a page
* where update/restore is necessary, absent some cache pressure. It's
* possible updates occurred after we selected this page for eviction,
* but it's unlikely and we don't try and manage that risk.
*
* Additionally, if we aren't trying to free space in the cache, scrub
* the page and keep it in memory.
*/
cache = conn->cache;
lookaside_retry = false;
lookaside_retryp = NULL;
if (closing)
LF_SET(WT_REC_VISIBILITY_ERR);
else if (!WT_PAGE_IS_INTERNAL(page) &&
!F_ISSET(S2BT(session), WT_BTREE_LOOKASIDE)) {
if (F_ISSET(conn, WT_CONN_IN_MEMORY))
LF_SET(WT_REC_IN_MEMORY |
WT_REC_SCRUB | WT_REC_UPDATE_RESTORE);
else if (WT_SESSION_BTREE_SYNC(session))
LF_SET(WT_REC_LOOKASIDE);
else if (!WT_IS_METADATA(session->dhandle)) {
LF_SET(WT_REC_UPDATE_RESTORE);
if (F_ISSET(cache, WT_CACHE_EVICT_SCRUB))
LF_SET(WT_REC_SCRUB);
/*
* If the cache is under pressure with many updates
* that can't be evicted, check if reconciliation
* suggests trying the lookaside table.
*/
if (F_ISSET(cache, WT_CACHE_EVICT_LOOKASIDE) &&
!F_ISSET(conn, WT_CONN_EVICTION_NO_LOOKASIDE))
lookaside_retryp = &lookaside_retry;
}
}
/* Reconcile the page. */
ret = __wt_reconcile(session, ref, NULL, flags, lookaside_retryp);
/*
* If attempting eviction during a checkpoint, we may successfully
* reconcile but then find that there are updates on the page too new
* to evict. Give up evicting in that case: checkpoint will include
* the reconciled page when it visits the parent.
*/
if (WT_SESSION_BTREE_SYNC(session) && !__wt_page_is_modified(page) &&
!__wt_txn_visible_all(session, page->modify->rec_max_txn,
page->modify->rec_max_timestamp))
return (__wt_set_return(session, EBUSY));
/*
* If reconciliation fails but reports it might succeed if we use the
* lookaside table, try again with the lookaside table, allowing the
* eviction of pages we'd otherwise have to retain in cache to support
* older readers.
*/
if (ret == EBUSY && lookaside_retry) {
LF_CLR(WT_REC_SCRUB | WT_REC_UPDATE_RESTORE);
LF_SET(WT_REC_LOOKASIDE);
ret = __wt_reconcile(session, ref, NULL, flags, NULL);
}
WT_RET(ret);
/*
* Give up on eviction during a checkpoint if the page splits.
*
* We get here if checkpoint reads a page with lookaside entries: if
* more of those entries are visible now than when the original
* eviction happened, the page could split. In most workloads, this is
* very unlikely. However, since checkpoint is partway through
* reconciling the parent page, a split can corrupt the checkpoint.
*/
if (WT_SESSION_BTREE_SYNC(session) &&
page->modify->rec_result == WT_PM_REC_MULTIBLOCK)
return (__wt_set_return(session, EBUSY));
/*
* Success: assert that the page is clean or reconciliation was
* configured to save updates.
*/
WT_ASSERT(session, !__wt_page_is_modified(page) ||
LF_ISSET(WT_REC_LOOKASIDE | WT_REC_UPDATE_RESTORE));
return (0);
}
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