/*
* __tree_walk_internal --
* Move to the next/previous page in the tree.
*/
static inline int
__tree_walk_internal(WT_SESSION_IMPL *session,
WT_REF **refp, uint64_t *walkcntp,
int (*skip_func)(WT_SESSION_IMPL *, WT_REF *, void *, bool *),
void *func_cookie, uint32_t flags)
{
WT_BTREE *btree;
WT_DECL_RET;
WT_PAGE_INDEX *pindex;
WT_REF *couple, *couple_orig, *ref;
uint32_t slot;
bool empty_internal, initial_descent, prev, skip;
btree = S2BT(session);
pindex = NULL;
empty_internal = initial_descent = false;
/*
* Tree walks are special: they look inside page structures that splits
* may want to free. Publish that the tree is active during this
* window.
*/
WT_ENTER_PAGE_INDEX(session);
/* Walk should never instantiate deleted pages. */
LF_SET(WT_READ_NO_EMPTY);
/*
* !!!
* Fast-truncate currently only works on row-store trees.
*/
if (btree->type != BTREE_ROW)
LF_CLR(WT_READ_TRUNCATE);
prev = LF_ISSET(WT_READ_PREV) ? 1 : 0;
/*
* There are multiple reasons and approaches to walking the in-memory
* tree:
*
* (1) finding pages to evict (the eviction server);
* (2) writing just dirty leaves or internal nodes (checkpoint);
* (3) discarding pages (close);
* (4) truncating pages in a range (fast truncate);
* (5) skipping pages based on outside information (compaction);
* (6) cursor scans (applications).
*
* Except for cursor scans and compaction, the walk is limited to the
* cache, no pages are read. In all cases, hazard pointers protect the
* walked pages from eviction.
*
* Walks use hazard-pointer coupling through the tree and that's OK
* (hazard pointers can't deadlock, so there's none of the usual
* problems found when logically locking up a btree). If the eviction
* thread tries to evict the active page, it fails because of our
* hazard pointer. If eviction tries to evict our parent, that fails
* because the parent has a child page that can't be discarded. We do
* play one game: don't couple up to our parent and then back down to a
* new leaf, couple to the next page to which we're descending, it
* saves a hazard-pointer swap for each cursor page movement.
*
* !!!
* NOTE: we depend on the fact it's OK to release a page we don't hold,
* that is, it's OK to release couple when couple is set to NULL.
*
* Take a copy of any held page and clear the return value. Remember
* the hazard pointer we're currently holding.
*
* Clear the returned value, it makes future error handling easier.
*/
couple = couple_orig = ref = *refp;
*refp = NULL;
/* If no page is active, begin a walk from the start/end of the tree. */
if (ref == NULL) {
restart: /*
* We can be here with a NULL or root WT_REF; the page release
* function handles them internally, don't complicate this code
* by calling them out.
*/
WT_ERR(__wt_page_release(session, couple, flags));
/*
* We're not supposed to walk trees without root pages. As this
* has not always been the case, assert to debug that change.
*/
WT_ASSERT(session, btree->root.page != NULL);
couple = couple_orig = ref = &btree->root;
initial_descent = true;
goto descend;
}
/*
* If the active page was the root, we've reached the walk's end; we
* only get here if we've returned the root to our caller, so we're
* holding no hazard pointers.
*/
if (__wt_ref_is_root(ref))
goto done;
/* Figure out the current slot in the WT_REF array. */
__ref_index_slot(session, ref, &pindex, &slot);
for (;;) {
/*
* If we're at the last/first slot on the internal page, return
* it in post-order traversal. Otherwise move to the next/prev
* slot and left/right-most element in that subtree.
*/
while ((prev && slot == 0) ||
(!prev && slot == pindex->entries - 1)) {
/* Ascend to the parent. */
__ref_ascend(session, &ref, &pindex, &slot);
/*
* If at the root and returning internal pages, return
* the root page, otherwise we're done. Regardless, no
* hazard pointer is required, release the one we hold.
*/
if (__wt_ref_is_root(ref)) {
WT_ERR(__wt_page_release(
session, couple, flags));
if (!LF_ISSET(WT_READ_SKIP_INTL))
*refp = ref;
goto done;
}
/*
* If we got all the way through an internal page and
* all of the child pages were deleted, mark it for
* eviction.
*/
if (empty_internal && pindex->entries > 1) {
__wt_page_evict_soon(session, ref);
empty_internal = false;
}
/*
* Optionally return internal pages. Swap our previous
* hazard pointer for the page we'll return. We don't
* handle restart or not-found returns, it would require
* additional complexity and is not a possible return:
* we're moving to the parent of the current child page,
* the parent can't have been evicted.
*/
if (!LF_ISSET(WT_READ_SKIP_INTL)) {
WT_ERR(__wt_page_swap(
session, couple, ref, flags));
*refp = ref;
goto done;
}
}
if (prev)
--slot;
else
++slot;
if (walkcntp != NULL)
++*walkcntp;
for (;;) {
/*
* Move to the next slot, and set the reference hint if
* it's wrong (used when we continue the walk). We don't
* always update the hints when splitting, it's expected
* for them to be incorrect in some workloads.
*/
ref = pindex->index[slot];
if (ref->pindex_hint != slot)
ref->pindex_hint = slot;
/*
* If we see any child states other than deleted, the
* page isn't empty.
*/
if (ref->state != WT_REF_DELETED &&
!LF_ISSET(WT_READ_TRUNCATE))
empty_internal = false;
if (LF_ISSET(WT_READ_CACHE)) {
/*
* Only look at unlocked pages in memory:
* fast-path some common cases.
*/
if (LF_ISSET(WT_READ_NO_WAIT) &&
ref->state != WT_REF_MEM)
break;
/* Skip lookaside pages if not requested. */
if (ref->state == WT_REF_LOOKASIDE &&
!LF_ISSET(WT_READ_LOOKASIDE))
break;
} else if (LF_ISSET(WT_READ_TRUNCATE)) {
/*
* Avoid pulling a deleted page back in to try
* to delete it again.
*/
if (ref->state == WT_REF_DELETED &&
__wt_delete_page_skip(session, ref, false))
break;
/*
* If deleting a range, try to delete the page
* without instantiating it.
*/
WT_ERR(__wt_delete_page(session, ref, &skip));
if (skip)
break;
empty_internal = false;
} else if (skip_func != NULL) {
WT_ERR(skip_func(session,
ref, func_cookie, &skip));
if (skip)
break;
} else {
/*
* Try to skip deleted pages visible to us.
*/
if (ref->state == WT_REF_DELETED &&
__wt_delete_page_skip(session, ref, false))
break;
}
ret = __wt_page_swap(session, couple, ref,
WT_READ_NOTFOUND_OK | WT_READ_RESTART_OK | flags);
/*
* Not-found is an expected return when only walking
* in-cache pages, or if we see a deleted page.
*/
if (ret == WT_NOTFOUND) {
ret = 0;
break;
}
/*
* The page we're moving to might have split, in which
* case move to the last position we held.
*/
if (ret == WT_RESTART) {
ret = 0;
/*
* If a cursor is setting up at the end of the
* tree, we can't use our parent page's index,
* because it may have already split; restart
* the walk.
*/
if (prev && initial_descent)
goto restart;
/*
* If a new walk that never coupled from the
* root to a new saved position in the tree,
* restart the walk.
*/
if (couple == &btree->root)
goto restart;
/*
* If restarting from some original position,
* repeat the increment or decrement we made at
* that time. Otherwise, couple is an internal
* page we've acquired after moving from that
* starting position and we can treat it as a
* new page. This works because we never acquire
* a hazard pointer on a leaf page we're not
* going to return to our caller, this will quit
* working if that ever changes.
*/
WT_ASSERT(session,
couple == couple_orig ||
WT_PAGE_IS_INTERNAL(couple->page));
ref = couple;
__ref_index_slot(session, ref, &pindex, &slot);
if (couple == couple_orig)
break;
}
WT_ERR(ret);
couple = ref;
/*
* A new page: configure for traversal of any internal
* page's children, else return the leaf page.
*/
if (WT_PAGE_IS_INTERNAL(ref->page)) {
descend: empty_internal = true;
/*
* There's a split race when a cursor is setting
* up at the end of the tree or moving backwards
* through the tree and descending a level. When
* splitting an internal page into its parent,
* we move the WT_REF structures and update the
* parent's page index before updating the split
* page's page index, and it's not an atomic
* update. A thread can read the parent page's
* replacement page index, then read the split
* page's original index, or the parent page's
* original and the split page's replacement.
*
* This isn't a problem for a cursor setting up
* at the start of the tree or moving forwards
* through the tree because we do right-hand
* splits on internal pages and the initial part
* of the split page's namespace won't change as
* part of a split. A thread reading the parent
* page's and split page's indexes will move to
* the same slot no matter what order of indexes
* are read.
*
* Handle a cursor setting up at the end of the
* tree or moving backwards through the tree.
*/
if (!prev) {
WT_INTL_INDEX_GET(
session, ref->page, pindex);
slot = 0;
} else if (initial_descent) {
if (!__ref_initial_descent_prev(
session, ref, &pindex))
goto restart;
slot = pindex->entries - 1;
} else {
__ref_descend_prev(
session, ref, &pindex);
slot = pindex->entries - 1;
}
continue;
}
/*
* The tree-walk restart code knows we return any leaf
* page we acquire (never hazard-pointer coupling on
* after acquiring a leaf page), and asserts no restart
* happens while holding a leaf page. This page must be
* returned to our caller.
*/
*refp = ref;
goto done;
}
}
done:
err: WT_LEAVE_PAGE_INDEX(session);
return (ret);
}
/*
* __clsm_enter_update --
* Make sure an LSM cursor is ready to perform an update.
*/
static int
__clsm_enter_update(WT_CURSOR_LSM *clsm)
{
WT_CURSOR *primary;
WT_LSM_CHUNK *primary_chunk;
WT_LSM_TREE *lsm_tree;
WT_SESSION_IMPL *session;
bool hard_limit, have_primary, ovfl;
lsm_tree = clsm->lsm_tree;
ovfl = false;
session = (WT_SESSION_IMPL *)clsm->iface.session;
if (clsm->nchunks == 0) {
primary = NULL;
have_primary = false;
} else {
primary = clsm->cursors[clsm->nchunks - 1];
primary_chunk = clsm->primary_chunk;
WT_ASSERT(session, F_ISSET(&session->txn, WT_TXN_HAS_ID));
have_primary = (primary != NULL && primary_chunk != NULL &&
(primary_chunk->switch_txn == WT_TXN_NONE ||
WT_TXNID_LT(session->txn.id, primary_chunk->switch_txn)));
}
/*
* In LSM there are multiple btrees active at one time. The tree
* switch code needs to use btree API methods, and it wants to
* operate on the btree for the primary chunk. Set that up now.
*
* If the primary chunk has grown too large, set a flag so the worker
* thread will switch when it gets a chance to avoid introducing high
* latency into application threads. Don't do this indefinitely: if a
* chunk grows twice as large as the configured size, block until it
* can be switched.
*/
hard_limit = F_ISSET(lsm_tree, WT_LSM_TREE_NEED_SWITCH);
if (have_primary) {
WT_ENTER_PAGE_INDEX(session);
WT_WITH_BTREE(session, ((WT_CURSOR_BTREE *)primary)->btree,
ovfl = __wt_btree_lsm_over_size(session, hard_limit ?
2 * lsm_tree->chunk_size : lsm_tree->chunk_size));
WT_LEAVE_PAGE_INDEX(session);
/* If there was no overflow, we're done. */
if (!ovfl)
return (0);
}
/* Request a switch. */
WT_RET(__wt_clsm_request_switch(clsm));
/* If we only overflowed the soft limit, we're done. */
if (have_primary && !hard_limit)
return (0);
WT_RET(__wt_clsm_await_switch(clsm));
return (0);
}
/*
* __wt_tree_walk --
* Move to the next/previous page in the tree.
*/
int
__wt_tree_walk(WT_SESSION_IMPL *session,
WT_REF **refp, uint64_t *walkcntp, uint32_t flags)
{
WT_BTREE *btree;
WT_DECL_RET;
WT_PAGE *page;
WT_PAGE_INDEX *pindex;
WT_REF *couple, *couple_orig, *ref;
int prev, skip;
uint32_t slot;
btree = S2BT(session);
/*
* Tree walks are special: they look inside page structures that splits
* may want to free. Publish that the tree is active during this
* window.
*/
WT_ENTER_PAGE_INDEX(session);
/*
* !!!
* Fast-truncate currently only works on row-store trees.
*/
if (btree->type != BTREE_ROW)
LF_CLR(WT_READ_TRUNCATE);
prev = LF_ISSET(WT_READ_PREV) ? 1 : 0;
/*
* There are multiple reasons and approaches to walking the in-memory
* tree:
*
* (1) finding pages to evict (the eviction server);
* (2) writing just dirty leaves or internal nodes (checkpoint);
* (3) discarding pages (close);
* (4) truncating pages in a range (fast truncate);
* (5) skipping pages based on outside information (compaction);
* (6) cursor scans (applications).
*
* Except for cursor scans and compaction, the walk is limited to the
* cache, no pages are read. In all cases, hazard pointers protect the
* walked pages from eviction.
*
* Walks use hazard-pointer coupling through the tree and that's OK
* (hazard pointers can't deadlock, so there's none of the usual
* problems found when logically locking up a btree). If the eviction
* thread tries to evict the active page, it fails because of our
* hazard pointer. If eviction tries to evict our parent, that fails
* because the parent has a child page that can't be discarded. We do
* play one game: don't couple up to our parent and then back down to a
* new leaf, couple to the next page to which we're descending, it
* saves a hazard-pointer swap for each cursor page movement.
*
* !!!
* NOTE: we depend on the fact it's OK to release a page we don't hold,
* that is, it's OK to release couple when couple is set to NULL.
*
* Take a copy of any held page and clear the return value. Remember
* the hazard pointer we're currently holding.
*
* We may be passed a pointer to btree->evict_page that we are clearing
* here. We check when discarding pages that we're not discarding that
* page, so this clear must be done before the page is released.
*/
couple = couple_orig = ref = *refp;
*refp = NULL;
/* If no page is active, begin a walk from the start of the tree. */
if (ref == NULL) {
ref = &btree->root;
if (ref->page == NULL)
goto done;
goto descend;
}
ascend: /*
* If the active page was the root, we've reached the walk's end.
* Release any hazard-pointer we're holding.
*/
if (__wt_ref_is_root(ref)) {
WT_ERR(__wt_page_release(session, couple, flags));
goto done;
}
/* Figure out the current slot in the WT_REF array. */
__wt_page_refp(session, ref, &pindex, &slot);
for (;;) {
/*
* If we're at the last/first slot on the page, return this page
* in post-order traversal. Otherwise we move to the next/prev
* slot and left/right-most element in its subtree.
*/
if ((prev && slot == 0) ||
(!prev && slot == pindex->entries - 1)) {
ref = ref->home->pg_intl_parent_ref;
/* Optionally skip internal pages. */
if (LF_ISSET(WT_READ_SKIP_INTL))
goto ascend;
/*
* We've ascended the tree and are returning an internal
* page. If it's the root, discard our hazard pointer,
* otherwise, swap our hazard pointer for the page we'll
* return.
*/
if (__wt_ref_is_root(ref))
WT_ERR(__wt_page_release(
session, couple, flags));
else {
/*
* Locate the reference to our parent page then
* swap our child hazard pointer for the parent.
* We don't handle restart or not-found returns.
* It would require additional complexity and is
* not a possible return: we're moving to the
* parent of the current child page, our parent
* reference can't have split or been evicted.
*/
__wt_page_refp(session, ref, &pindex, &slot);
if ((ret = __wt_page_swap(
session, couple, ref, flags)) != 0) {
WT_TRET(__wt_page_release(
session, couple, flags));
WT_ERR(ret);
}
}
*refp = ref;
goto done;
}
if (prev)
--slot;
else
++slot;
if (walkcntp != NULL)
++*walkcntp;
for (;;) {
ref = pindex->index[slot];
if (LF_ISSET(WT_READ_CACHE)) {
/*
* Only look at unlocked pages in memory:
* fast-path some common cases.
*/
if (LF_ISSET(WT_READ_NO_WAIT) &&
ref->state != WT_REF_MEM)
break;
} else if (LF_ISSET(WT_READ_TRUNCATE)) {
/*
* Avoid pulling a deleted page back in to try
* to delete it again.
*/
if (ref->state == WT_REF_DELETED &&
__wt_delete_page_skip(session, ref))
break;
/*
* If deleting a range, try to delete the page
* without instantiating it.
*/
WT_ERR(__wt_delete_page(session, ref, &skip));
if (skip)
break;
} else if (LF_ISSET(WT_READ_COMPACT)) {
/*
* Skip deleted pages, rewriting them doesn't
* seem useful.
*/
if (ref->state == WT_REF_DELETED)
break;
/*
* If the page is in-memory, we want to look at
* it (it may have been modified and written,
* and the current location is the interesting
* one in terms of compaction, not the original
* location). If the page isn't in-memory, test
* if the page will help with compaction, don't
* read it if we don't have to.
*/
if (ref->state == WT_REF_DISK) {
WT_ERR(__wt_compact_page_skip(
session, ref, &skip));
if (skip)
break;
}
} else {
/*
* Try to skip deleted pages visible to us.
*/
if (ref->state == WT_REF_DELETED &&
__wt_delete_page_skip(session, ref))
break;
}
ret = __wt_page_swap(session, couple, ref, flags);
/*
* Not-found is an expected return when only walking
* in-cache pages.
*/
if (ret == WT_NOTFOUND) {
ret = 0;
break;
}
/*
* The page we're moving to might have split, in which
* case move to the last position we held.
*/
if (ret == WT_RESTART) {
ret = 0;
/*
* If a new walk that never coupled from the
* root to a new saved position in the tree,
* restart the walk.
*/
if (couple == &btree->root) {
ref = &btree->root;
if (ref->page == NULL)
goto done;
goto descend;
}
/*
* If restarting from some original position,
* repeat the increment or decrement we made at
* that time. Otherwise, couple is an internal
* page we've acquired after moving from that
* starting position and we can treat it as a
* new page. This works because we never acquire
* a hazard pointer on a leaf page we're not
* going to return to our caller, this will quit
* working if that ever changes.
*/
WT_ASSERT(session,
couple == couple_orig ||
WT_PAGE_IS_INTERNAL(couple->page));
ref = couple;
__wt_page_refp(session, ref, &pindex, &slot);
if (couple == couple_orig)
break;
}
WT_ERR(ret);
/*
* A new page: configure for traversal of any internal
* page's children, else return the leaf page.
*/
descend: couple = ref;
page = ref->page;
if (page->type == WT_PAGE_ROW_INT ||
page->type == WT_PAGE_COL_INT) {
WT_INTL_INDEX_GET(session, page, pindex);
slot = prev ? pindex->entries - 1 : 0;
} else {
*refp = ref;
goto done;
}
}
}
done:
err: WT_LEAVE_PAGE_INDEX(session);
return (ret);
}
/*
* __tree_walk_internal --
* Move to the next/previous page in the tree.
*/
static inline int
__tree_walk_internal(WT_SESSION_IMPL *session,
WT_REF **refp, uint64_t *walkcntp, uint64_t *skipleafcntp, uint32_t flags)
{
WT_BTREE *btree;
WT_DECL_RET;
WT_PAGE_INDEX *pindex;
WT_REF *couple, *couple_orig, *ref;
bool empty_internal, prev, skip;
uint32_t slot;
btree = S2BT(session);
empty_internal = false;
/*
* Tree walks are special: they look inside page structures that splits
* may want to free. Publish that the tree is active during this
* window.
*/
WT_ENTER_PAGE_INDEX(session);
/* Walk should never instantiate deleted pages. */
LF_SET(WT_READ_NO_EMPTY);
/*
* !!!
* Fast-truncate currently only works on row-store trees.
*/
if (btree->type != BTREE_ROW)
LF_CLR(WT_READ_TRUNCATE);
prev = LF_ISSET(WT_READ_PREV) ? 1 : 0;
/*
* There are multiple reasons and approaches to walking the in-memory
* tree:
*
* (1) finding pages to evict (the eviction server);
* (2) writing just dirty leaves or internal nodes (checkpoint);
* (3) discarding pages (close);
* (4) truncating pages in a range (fast truncate);
* (5) skipping pages based on outside information (compaction);
* (6) cursor scans (applications).
*
* Except for cursor scans and compaction, the walk is limited to the
* cache, no pages are read. In all cases, hazard pointers protect the
* walked pages from eviction.
*
* Walks use hazard-pointer coupling through the tree and that's OK
* (hazard pointers can't deadlock, so there's none of the usual
* problems found when logically locking up a btree). If the eviction
* thread tries to evict the active page, it fails because of our
* hazard pointer. If eviction tries to evict our parent, that fails
* because the parent has a child page that can't be discarded. We do
* play one game: don't couple up to our parent and then back down to a
* new leaf, couple to the next page to which we're descending, it
* saves a hazard-pointer swap for each cursor page movement.
*
* !!!
* NOTE: we depend on the fact it's OK to release a page we don't hold,
* that is, it's OK to release couple when couple is set to NULL.
*
* Take a copy of any held page and clear the return value. Remember
* the hazard pointer we're currently holding.
*
* We may be passed a pointer to btree->evict_page that we are clearing
* here. We check when discarding pages that we're not discarding that
* page, so this clear must be done before the page is released.
*/
couple = couple_orig = ref = *refp;
*refp = NULL;
/* If no page is active, begin a walk from the start of the tree. */
if (ref == NULL) {
ref = &btree->root;
if (ref->page == NULL)
goto done;
goto descend;
}
/*
* If the active page was the root, we've reached the walk's end.
* Release any hazard-pointer we're holding.
*/
if (__wt_ref_is_root(ref)) {
WT_ERR(__wt_page_release(session, couple, flags));
goto done;
}
/* Figure out the current slot in the WT_REF array. */
__ref_index_slot(session, ref, &pindex, &slot);
for (;;) {
/*
* If we're at the last/first slot on the internal page, return
* it in post-order traversal. Otherwise move to the next/prev
* slot and left/right-most element in that subtree.
*/
while ((prev && slot == 0) ||
(!prev && slot == pindex->entries - 1)) {
/* Ascend to the parent. */
__page_ascend(session, &ref, &pindex, &slot);
/*
* If we got all the way through an internal page and
* all of the child pages were deleted, mark it for
* eviction.
*/
if (empty_internal && pindex->entries > 1) {
__wt_page_evict_soon(ref->page);
empty_internal = false;
}
/*
* If at the root and returning internal pages, return
* the root page, otherwise we're done. Regardless, no
* hazard pointer is required, release the one we hold.
*/
if (__wt_ref_is_root(ref)) {
WT_ERR(__wt_page_release(
session, couple, flags));
if (!LF_ISSET(WT_READ_SKIP_INTL))
*refp = ref;
goto done;
}
/*
* Optionally return internal pages. Swap our previous
* hazard pointer for the page we'll return. We don't
* handle restart or not-found returns, it would require
* additional complexity and is not a possible return:
* we're moving to the parent of the current child page,
* the parent can't have been evicted.
*/
if (!LF_ISSET(WT_READ_SKIP_INTL)) {
WT_ERR(__wt_page_swap(
session, couple, ref, flags));
*refp = ref;
goto done;
}
}
if (prev)
--slot;
else
++slot;
if (walkcntp != NULL)
++*walkcntp;
for (;;) {
/*
* Move to the next slot, and set the reference hint if
* it's wrong (used when we continue the walk). We don't
* update those hints when splitting, so it's common for
* them to be incorrect in some workloads.
*/
ref = pindex->index[slot];
if (ref->pindex_hint != slot)
ref->pindex_hint = slot;
/*
* If we see any child states other than deleted, the
* page isn't empty.
*/
if (ref->state != WT_REF_DELETED &&
!LF_ISSET(WT_READ_TRUNCATE))
empty_internal = false;
if (LF_ISSET(WT_READ_CACHE)) {
/*
* Only look at unlocked pages in memory:
* fast-path some common cases.
*/
if (LF_ISSET(WT_READ_NO_WAIT) &&
ref->state != WT_REF_MEM)
break;
} else if (LF_ISSET(WT_READ_TRUNCATE)) {
/*
* Avoid pulling a deleted page back in to try
* to delete it again.
*/
if (ref->state == WT_REF_DELETED &&
__wt_delete_page_skip(session, ref, false))
break;
/*
* If deleting a range, try to delete the page
* without instantiating it.
*/
WT_ERR(__wt_delete_page(session, ref, &skip));
if (skip)
break;
empty_internal = false;
} else if (LF_ISSET(WT_READ_COMPACT)) {
/*
* Skip deleted pages, rewriting them doesn't
* seem useful.
*/
if (ref->state == WT_REF_DELETED)
break;
/*
* If the page is in-memory, we want to look at
* it (it may have been modified and written,
* and the current location is the interesting
* one in terms of compaction, not the original
* location). If the page isn't in-memory, test
* if the page will help with compaction, don't
* read it if we don't have to.
*/
if (ref->state == WT_REF_DISK) {
WT_ERR(__wt_compact_page_skip(
session, ref, &skip));
if (skip)
break;
}
} else {
/*
* Try to skip deleted pages visible to us.
*/
if (ref->state == WT_REF_DELETED &&
__wt_delete_page_skip(session, ref, false))
break;
}
/*
* Optionally skip leaf pages: skip all leaf pages if
* WT_READ_SKIP_LEAF is set, when the skip-leaf-count
* variable is non-zero, skip some count of leaf pages.
* If this page is disk-based, crack the cell to figure
* out it's a leaf page without reading it.
*
* If skipping some number of leaf pages, decrement the
* count of pages to zero, and then take the next leaf
* page we can. Be cautious around the page decrement,
* if for some reason don't take this particular page,
* we can take the next one, and, there are additional
* tests/decrements when we're about to return a leaf
* page.
*/
if (skipleafcntp != NULL || LF_ISSET(WT_READ_SKIP_LEAF))
if (__ref_is_leaf(ref)) {
if (LF_ISSET(WT_READ_SKIP_LEAF))
break;
if (*skipleafcntp > 0) {
--*skipleafcntp;
break;
}
}
ret = __wt_page_swap(session, couple, ref,
WT_READ_NOTFOUND_OK | WT_READ_RESTART_OK | flags);
/*
* Not-found is an expected return when only walking
* in-cache pages, or if we see a deleted page.
*/
if (ret == WT_NOTFOUND) {
ret = 0;
break;
}
/*
* The page we're moving to might have split, in which
* case move to the last position we held.
*/
if (ret == WT_RESTART) {
ret = 0;
/*
* If a new walk that never coupled from the
* root to a new saved position in the tree,
* restart the walk.
*/
if (couple == &btree->root) {
ref = &btree->root;
if (ref->page == NULL)
goto done;
goto descend;
}
/*
* If restarting from some original position,
* repeat the increment or decrement we made at
* that time. Otherwise, couple is an internal
* page we've acquired after moving from that
* starting position and we can treat it as a
* new page. This works because we never acquire
* a hazard pointer on a leaf page we're not
* going to return to our caller, this will quit
* working if that ever changes.
*/
WT_ASSERT(session,
couple == couple_orig ||
WT_PAGE_IS_INTERNAL(couple->page));
ref = couple;
__ref_index_slot(session, ref, &pindex, &slot);
if (couple == couple_orig)
break;
}
WT_ERR(ret);
/*
* A new page: configure for traversal of any internal
* page's children, else return the leaf page.
*/
if (WT_PAGE_IS_INTERNAL(ref->page)) {
descend: couple = ref;
empty_internal = true;
__page_descend(
session, ref->page, &pindex, &slot, prev);
} else {
/*
* Optionally skip leaf pages, the second half.
* We didn't have an on-page cell to figure out
* if it was a leaf page, we had to acquire the
* hazard pointer and look at the page.
*/
if (skipleafcntp != NULL ||
LF_ISSET(WT_READ_SKIP_LEAF)) {
couple = ref;
if (LF_ISSET(WT_READ_SKIP_LEAF))
break;
if (*skipleafcntp > 0) {
--*skipleafcntp;
break;
}
}
*refp = ref;
goto done;
}
}
}
done:
err: WT_LEAVE_PAGE_INDEX(session);
return (ret);
}