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/*-
* Copyright (c) 2014-2016 MongoDB, Inc.
* Copyright (c) 2008-2014 WiredTiger, Inc.
* All rights reserved.
*
* See the file LICENSE for redistribution information.
*/
#include "wt_internal.h"
/*
* __compact_rewrite --
* Return if a page needs to be re-written.
*/
static int
__compact_rewrite(WT_SESSION_IMPL *session, WT_REF *ref, bool *skipp)
{
WT_BM *bm;
WT_DECL_RET;
WT_MULTI *multi;
WT_PAGE *page;
WT_PAGE_MODIFY *mod;
size_t addr_size;
uint32_t i;
const uint8_t *addr;
*skipp = true; /* Default skip. */
bm = S2BT(session)->bm;
page = ref->page;
mod = page->modify;
/*
* Ignore the root: it may not have a replacement address, and besides,
* if anything else gets written, so will it.
*/
if (__wt_ref_is_root(ref))
return (0);
/* Ignore currently dirty pages, they will be written regardless. */
if (__wt_page_is_modified(page))
return (0);
/*
* If the page is clean, test the original addresses.
* If the page is a replacement, test the replacement addresses.
* Ignore empty pages, they get merged into the parent.
*/
if (mod == NULL || mod->rec_result == 0) {
__wt_ref_info(ref, &addr, &addr_size, NULL);
if (addr == NULL)
return (0);
return (
bm->compact_page_skip(bm, session, addr, addr_size, skipp));
}
/*
* The page's modification information can change underfoot if the page
* is being reconciled, serialize with reconciliation.
*/
if (mod->rec_result == WT_PM_REC_REPLACE ||
mod->rec_result == WT_PM_REC_MULTIBLOCK)
__wt_writelock(session, &page->page_lock);
if (mod->rec_result == WT_PM_REC_REPLACE)
ret = bm->compact_page_skip(bm, session,
mod->mod_replace.addr, mod->mod_replace.size, skipp);
if (mod->rec_result == WT_PM_REC_MULTIBLOCK)
for (multi = mod->mod_multi,
i = 0; i < mod->mod_multi_entries; ++multi, ++i) {
if (multi->disk_image != NULL)
continue;
if ((ret = bm->compact_page_skip(bm, session,
multi->addr.addr, multi->addr.size, skipp)) != 0)
break;
if (!*skipp)
break;
}
if (mod->rec_result == WT_PM_REC_REPLACE ||
mod->rec_result == WT_PM_REC_MULTIBLOCK)
__wt_writeunlock(session, &page->page_lock);
return (ret);
}
/*
* __wt_compact --
* Compact a file.
*/
int
__wt_compact(WT_SESSION_IMPL *session)
{
WT_BM *bm;
WT_BTREE *btree;
WT_DECL_RET;
WT_REF *ref;
u_int i;
bool skip;
btree = S2BT(session);
bm = btree->bm;
ref = NULL;
WT_STAT_DATA_INCR(session, session_compact);
/*
* Check if compaction might be useful -- the API layer will quit trying
* to compact the data source if we make no progress, set a flag if the
* block layer thinks compaction is possible.
*/
WT_RET(bm->compact_skip(bm, session, &skip));
if (skip)
return (0);
/*
* Reviewing in-memory pages requires looking at page reconciliation
* results, because we care about where the page is stored now, not
* where the page was stored when we first read it into the cache.
* We need to ensure we don't race with page reconciliation as it's
* writing the page modify information.
*
* There are two ways we call reconciliation: checkpoints and eviction.
* Get the tree's flush lock which blocks threads writing pages for
* checkpoints.
*/
__wt_spin_lock(session, &btree->flush_lock);
/* Walk the tree reviewing pages to see if they should be re-written. */
for (i = 0;;) {
/* Periodically check if we've run out of time. */
if (++i > 100) {
WT_ERR(__wt_session_compact_check_timeout(session));
i = 0;
}
/*
* Pages read for compaction aren't "useful"; don't update the
* read generation of pages already in memory, and if a page is
* read, set its generation to a low value so it is evicted
* quickly.
*/
WT_ERR(__wt_tree_walk(session, &ref,
WT_READ_COMPACT | WT_READ_NO_GEN | WT_READ_WONT_NEED));
if (ref == NULL)
break;
WT_ERR(__compact_rewrite(session, ref, &skip));
if (skip)
continue;
session->compact_state = WT_COMPACT_SUCCESS;
/* Rewrite the page: mark the page and tree dirty. */
WT_ERR(__wt_page_modify_init(session, ref->page));
__wt_page_modify_set(session, ref->page);
WT_STAT_DATA_INCR(session, btree_compact_rewrite);
}
err: if (ref != NULL)
WT_TRET(__wt_page_release(session, ref, 0));
/* Unblock threads writing leaf pages. */
__wt_spin_unlock(session, &btree->flush_lock);
return (ret);
}
/*
* __wt_compact_page_skip --
* Return if compaction requires we read this page.
*/
int
__wt_compact_page_skip(WT_SESSION_IMPL *session, WT_REF *ref, bool *skipp)
{
WT_BM *bm;
WT_DECL_RET;
size_t addr_size;
u_int type;
const uint8_t *addr;
/*
* Skip deleted pages, rewriting them doesn't seem useful; in a better
* world we'd write the parent to delete the page.
*/
if (ref->state == WT_REF_DELETED) {
*skipp = true;
return (0);
}
*skipp = false; /* Default to reading */
/*
* 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).
*
* This test could be combined with the next one, but this is a cheap
* test and the next one is expensive.
*/
if (ref->state != WT_REF_DISK)
return (0);
/*
* There's nothing to prevent the WT_REF state from changing underfoot,
* which can change its address. For example, the WT_REF address might
* reference an on-page cell, and page eviction can free that memory.
* Lock the WT_REF so we can look at its address.
*/
if (!__wt_atomic_casv32(&ref->state, WT_REF_DISK, WT_REF_LOCKED))
return (0);
/*
* The page is on disk, so there had better be an address; assert that
* fact, test at run-time to avoid the core dump.
*
* Internal pages must be read to walk the tree; ask the block-manager
* if it's useful to rewrite leaf pages, don't do the I/O if a rewrite
* won't help.
*/
__wt_ref_info(ref, &addr, &addr_size, &type);
WT_ASSERT(session, addr != NULL);
if (addr != NULL && type != WT_CELL_ADDR_INT) {
bm = S2BT(session)->bm;
ret = bm->compact_page_skip(
bm, session, addr, addr_size, skipp);
}
/*
* Reset the WT_REF state and push the change. The full-barrier isn't
* necessary, but it's better to keep pages in circulation than not.
*/
ref->state = WT_REF_DISK;
WT_FULL_BARRIER();
return (ret);
}
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