/*
* __compact_start --
* Start object compaction.
*/
static int
__compact_start(WT_SESSION_IMPL *session)
{
WT_BM *bm;
bm = S2BT(session)->bm;
return (bm->compact_start(bm, session));
}
/*
* __wt_compact --
* Compact a file.
*/
int
__wt_compact(WT_SESSION_IMPL *session, const char *cfg[])
{
WT_BM *bm;
WT_BTREE *btree;
WT_DECL_RET;
WT_REF *ref;
bool block_manager_begin, skip;
WT_UNUSED(cfg);
btree = S2BT(session);
bm = btree->bm;
ref = NULL;
block_manager_begin = false;
WT_STAT_FAST_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 three ways we call reconciliation: checkpoints, threads
* writing leaf pages (usually in preparation for a checkpoint or if
* closing a file), and eviction.
*
* We're holding the schema lock which serializes with checkpoints.
*/
WT_ASSERT(session, F_ISSET(session, WT_SESSION_LOCKED_SCHEMA));
/*
* Get the tree handle's flush lock which blocks threads writing leaf
* pages.
*/
__wt_spin_lock(session, &btree->flush_lock);
/* Start compaction. */
WT_ERR(bm->compact_start(bm, session));
block_manager_begin = true;
/* Walk the tree reviewing pages to see if they should be re-written. */
for (;;) {
/*
* 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_FAST_DATA_INCR(session, btree_compact_rewrite);
}
err:
if (ref != NULL)
WT_TRET(__wt_page_release(session, ref, 0));
if (block_manager_begin)
WT_TRET(bm->compact_end(bm, session));
/* Unblock threads writing leaf pages. */
__wt_spin_unlock(session, &btree->flush_lock);
return (ret);
}
/*对文件进行compact操作*/
int __wt_compact(WT_SESSION_IMPL* session, const char* cfg[])
{
WT_BM *bm;
WT_BTREE *btree;
WT_CONNECTION_IMPL *conn;
WT_DECL_RET;
WT_REF *ref;
int block_manager_begin, evict_reset, skip;
WT_UNUSED(cfg);
conn = S2C(session);
btree = S2BT(session);
bm = btree->bm;
ref = NULL;
block_manager_begin = 0;
WT_STAT_FAST_DATA_INCR(session, session_compact);
/*检查bm对相应的blocks是否可以compact,如果不可以，直接返回*/
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 three ways we call reconciliation: checkpoints, threads
* writing leaf pages (usually in preparation for a checkpoint or if
* closing a file), and eviction.
*
* We're holding the schema lock which serializes with checkpoints.
*/
WT_ASSERT(session, F_ISSET(session, WT_SESSION_SCHEMA_LOCKED));
/*获得btree flusk_lock,防止在文件空间compact被其他线程flush*/
__wt_spin_lock(session, &btree->flush_lock);
conn->compact_in_memory_pass = 1;
WT_ERR(__wt_evict_file_exclusive_on(session, &evict_reset));
if (evict_reset)
__wt_evict_file_exclusive_off(session);
WT_ERR(bm->compact_start(bm, session));
block_manager_begin = 1;
session->compaction = 1;
for (;;){
WT_ERR(__wt_tree_walk(session, &ref, NULL, WT_READ_COMPACT | WT_READ_NO_GEN | WT_READ_WONT_NEED));
if (ref == NULL)
break;
/*进行compact标记*/
WT_ERR(__compact_rewrite(session, ref, &skip));
if (skip)
continue;
/*如果需要compact的page需要标记为脏page,通过内存驱逐来回写compact结果*/
WT_ERR(__wt_page_modify_init(session, ref->page));
__wt_page_modify_set(session, ref->page);
WT_STAT_FAST_DATA_INCR(session, btree_compact_rewrite);
}
err:
if (ref != NULL)
WT_TRET(__wt_page_release(session, ref, 0));
/*结束compact动作*/
if (block_manager_begin)
WT_TRET(bm->compact_end(bm, session));
/*
* Unlock will be a release barrier, use it to update the compaction
* status for reconciliation.
*/
conn->compact_in_memory_pass = 0;
__wt_spin_unlock(session, &btree->flush_lock);
return ret;
}
/*
* __wt_compact --
* Compact a file.
*/
int
__wt_compact(WT_SESSION_IMPL *session, const char *cfg[])
{
WT_BM *bm;
WT_BTREE *btree;
WT_CONNECTION_IMPL *conn;
WT_DECL_RET;
WT_REF *ref;
int block_manager_begin, evict_reset, skip;
WT_UNUSED(cfg);
conn = S2C(session);
btree = S2BT(session);
bm = btree->bm;
ref = NULL;
block_manager_begin = 0;
WT_STAT_FAST_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 three ways we call reconciliation: checkpoints, threads
* writing leaf pages (usually in preparation for a checkpoint or if
* closing a file), and eviction.
*
* We're holding the schema lock which serializes with checkpoints.
*/
WT_ASSERT(session, F_ISSET(session, WT_SESSION_SCHEMA_LOCKED));
/*
* Get the tree handle's flush lock which blocks threads writing leaf
* pages.
*/
__wt_spin_lock(session, &btree->flush_lock);
/*
* That leaves eviction, we don't want to block eviction. Set a flag
* so reconciliation knows compaction is running. If reconciliation
* sees the flag it locks the page it's writing, we acquire the same
* lock when reading the page's modify information, serializing access.
* The same page lock blocks work on the page, but compaction is an
* uncommon, heavy-weight operation. If it's ever a problem, there's
* no reason we couldn't use an entirely separate lock than the page
* lock.
*
* We also need to ensure we don't race with an on-going reconciliation.
* After we set the flag, wait for eviction of this file to drain, and
* then let eviction continue;
*/
conn->compact_in_memory_pass = 1;
WT_ERR(__wt_evict_file_exclusive_on(session, &evict_reset));
if (evict_reset)
__wt_evict_file_exclusive_off(session);
/* Start compaction. */
WT_ERR(bm->compact_start(bm, session));
block_manager_begin = 1;
/* Walk the tree reviewing pages to see if they should be re-written. */
session->compaction = 1;
for (;;) {
/*
* 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, NULL,
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;
/* 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_FAST_DATA_INCR(session, btree_compact_rewrite);
}
err: if (ref != NULL)
WT_TRET(__wt_page_release(session, ref, 0));
if (block_manager_begin)
WT_TRET(bm->compact_end(bm, session));
/*
* Unlock will be a release barrier, use it to update the compaction
* status for reconciliation.
*/
conn->compact_in_memory_pass = 0;
__wt_spin_unlock(session, &btree->flush_lock);
return (ret);
}