PostgreSQL的vacuum过程中heap_vacuum_rel函数分析
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本节简单介绍了PostgreSQL手工执行vacuum的实现逻辑,主要分析了ExecVacuum->vacuum->vacuum_rel->heap_vacuum_rel函数的实现逻辑。
一、数据结构
宏定义
Vacuum和Analyze命令选项
/* ----------------------
* Vacuum and Analyze Statements
* Vacuum和Analyze命令选项
*
* Even though these are nominally two statements, it's convenient to use
* just one node type for both. Note that at least one of VACOPT_VACUUM
* and VACOPT_ANALYZE must be set in options.
* 虽然在这里有两种不同的语句,但只需要使用统一的Node类型即可.
* 注意至少VACOPT_VACUUM/VACOPT_ANALYZE在选项中设置.
* ----------------------
*/
typedef enum VacuumOption
{
VACOPT_VACUUM = 1 << 0, /* do VACUUM */
VACOPT_ANALYZE = 1 << 1, /* do ANALYZE */
VACOPT_VERBOSE = 1 << 2, /* print progress info */
VACOPT_FREEZE = 1 << 3, /* FREEZE option */
VACOPT_FULL = 1 << 4, /* FULL (non-concurrent) vacuum */
VACOPT_SKIP_LOCKED = 1 << 5, /* skip if cannot get lock */
VACOPT_SKIPTOAST = 1 << 6, /* don't process the TOAST table, if any */
VACOPT_DISABLE_PAGE_SKIPPING = 1 << 7 /* don't skip any pages */
} VacuumOption;VacuumStmt
存储vacuum命令的option&Relation链表
typedef struct VacuumStmt
{
NodeTag type;//Tag
//VacuumOption位标记
int options; /* OR of VacuumOption flags */
//VacuumRelation链表,如为NIL-->所有Relation.
List *rels; /* list of VacuumRelation, or NIL for all */
} VacuumStmt;VacuumParams
vacuum命令参数
/*
* Parameters customizing behavior of VACUUM and ANALYZE.
* 客户端调用VACUUM/ANALYZE时的定制化参数
*/
typedef struct VacuumParams
{
//最小freeze age,-1表示使用默认
int freeze_min_age; /* min freeze age, -1 to use default */
//扫描整个table的freeze age
int freeze_table_age; /* age at which to scan whole table */
//最小的multixact freeze age,-1表示默认
int multixact_freeze_min_age; /* min multixact freeze age, -1 to
* use default */
//扫描全表的freeze age,-1表示默认
int multixact_freeze_table_age; /* multixact age at which to scan
* whole table */
//是否强制wraparound?
bool is_wraparound; /* force a for-wraparound vacuum */
//以毫秒为单位的最小执行阈值
int log_min_duration; /* minimum execution threshold in ms at
* which verbose logs are activated, -1
* to use default */
} VacuumParams;VacuumRelation
VACUUM/ANALYZE命令的目标表信息
/*
* Info about a single target table of VACUUM/ANALYZE.
* VACUUM/ANALYZE命令的目标表信息.
*
* If the OID field is set, it always identifies the table to process.
* Then the relation field can be NULL; if it isn't, it's used only to report
* failure to open/lock the relation.
* 如设置了OID字段,该值通常是将要处理的数据表.
* 那么关系字段可以为空;如果不是，则仅用于报告未能打开/锁定关系。
*/
typedef struct VacuumRelation
{
NodeTag type;
RangeVar *relation; /* table name to process, or NULL */
Oid oid; /* table's OID; InvalidOid if not looked up */
List *va_cols; /* list of column names, or NIL for all */
} VacuumRelation;BufferAccessStrategy
Buffer访问策略对象
/*
* Buffer identifiers.
* Buffer标识符
*
* Zero is invalid, positive is the index of a shared buffer (1..NBuffers),
* negative is the index of a local buffer (-1 .. -NLocBuffer).
* 0表示无效,正整数表示共享buffer的索引(1..N),
* 负数是本地buffer的索引(-1..-N)
*/
typedef int Buffer;
#define InvalidBuffer 0
/*
* Buffer access strategy objects.
* Buffer访问策略对象
*
* BufferAccessStrategyData is private to freelist.c
* BufferAccessStrategyData对freelist.c来说是私有的
*/
typedef struct BufferAccessStrategyData *BufferAccessStrategy;
/*
* Private (non-shared) state for managing a ring of shared buffers to re-use.
* This is currently the only kind of BufferAccessStrategy object, but someday
* we might have more kinds.
* 私有状态,用于管理可重用的环形缓冲区.
* 目前只有这么一种缓冲区访问策略对象,但未来某一天可以拥有更多.
*/
typedef struct BufferAccessStrategyData
{
/* Overall strategy type */
//全局的策略类型
BufferAccessStrategyType btype;
/* Number of elements in buffers[] array */
//buffers[]中的元素个数
int ring_size;
/*
* Index of the "current" slot in the ring, ie, the one most recently
* returned by GetBufferFromRing.
* 环形缓冲区中当前slot的索引,最近访问的通过函数GetBufferFromRing返回.
*/
int current;
/*
* True if the buffer just returned by StrategyGetBuffer had been in the
* ring already.
* 如正好通过StrategyGetBuffer返回的buffer已在环形缓冲区中,则返回T
*/
bool current_was_in_ring;
/*
* Array of buffer numbers. InvalidBuffer (that is, zero) indicates we
* have not yet selected a buffer for this ring slot. For allocation
* simplicity this is palloc'd together with the fixed fields of the
* struct.
* buffer编号数组.
* InvalidBuffer(即:0)表示我们还没有为该slot选择buffer.
* 为了分配的简单性，这是palloc'd与结构的固定字段。
*/
Buffer buffers[FLEXIBLE_ARRAY_MEMBER];
} BufferAccessStrategyData;
//Block结构体指针
typedef void *Block;
/* Possible arguments for GetAccessStrategy() */
//GetAccessStrategy()函数可取值的参数
typedef enum BufferAccessStrategyType
{
//常规的随机访问
BAS_NORMAL, /* Normal random access */
//大规模的只读扫描
BAS_BULKREAD, /* Large read-only scan (hint bit updates are
* ok) */
//大量的多块写(如 COPY IN)
BAS_BULKWRITE, /* Large multi-block write (e.g. COPY IN) */
//VACUUM
BAS_VACUUM /* VACUUM */
} BufferAccessStrategyType;LVRelStats
typedef struct LVRelStats
{
/* hasindex = true means two-pass strategy; false means one-pass */
//T表示two-pass strategy,F表示one-pass strategy
bool hasindex;
/* Overall statistics about rel */
//rel的全局统计信息
//pg_class.relpages的上一个值
BlockNumber old_rel_pages; /* previous value of pg_class.relpages */
//pages的总数
BlockNumber rel_pages; /* total number of pages */
//扫描的pages
BlockNumber scanned_pages; /* number of pages we examined */
//由于pin跳过的pages
BlockNumber pinskipped_pages; /* # of pages we skipped due to a pin */
//跳过的frozen pages
BlockNumber frozenskipped_pages; /* # of frozen pages we skipped */
//计算其元组的pages
BlockNumber tupcount_pages; /* pages whose tuples we counted */
//pg_class.reltuples的前值
double old_live_tuples; /* previous value of pg_class.reltuples */
//新估算的总元组数
double new_rel_tuples; /* new estimated total # of tuples */
//新估算的存活元组数
double new_live_tuples; /* new estimated total # of live tuples */
//新估算的废弃元组数
double new_dead_tuples; /* new estimated total # of dead tuples */
//已清除的pages
BlockNumber pages_removed;
//已删除的tuples
double tuples_deleted;
//实际上是非空page + 1
BlockNumber nonempty_pages; /* actually, last nonempty page + 1 */
/* List of TIDs of tuples we intend to delete */
/* NB: this list is ordered by TID address */
//将要删除的元组TIDs链表
//注意:该链表已使用TID地址排序
//当前的入口/条目数
int num_dead_tuples; /* current # of entries */
//数组中已分配的slots(最大已废弃元组数)
int max_dead_tuples; /* # slots allocated in array */
//ItemPointerData数组
ItemPointer dead_tuples; /* array of ItemPointerData */
//扫描的索引数
int num_index_scans;
//最后被清除的事务ID
TransactionId latestRemovedXid;
//是否存在waiter?
bool lock_waiter_detected;
} LVRelStats;PGRUsage
pg_rusage_init/pg_rusage_show的状态结构体
/* State structure for pg_rusage_init/pg_rusage_show */
//pg_rusage_init/pg_rusage_show的状态结构体
typedef struct PGRUsage
{
struct timeval tv;
struct rusage ru;
} PGRUsage;
struct rusage
{
struct timeval ru_utime; /* user time used */
struct timeval ru_stime; /* system time used */
};
struct timeval
{
__time_t tv_sec; /* 秒数.Seconds. */
__suseconds_t tv_usec; /* 微秒数.Microseconds-->这个英文注释有问题. */
};二、源码解读
heap_vacuum_rel() — 为heap relation执行VACUUM
大体逻辑如下:
1.初始化相关变量,如本地变量/日志记录级别/访问策略等
2.调用vacuum_set_xid_limits计算最老的xmin和冻结截止点
3.判断是否执行全表(不跳过pages)扫描,标记变量为aggressive
4.初始化统计信息结构体vacrelstats
5.打开索引,执行函数lazy_scan_heap进行vacuuming,关闭索引
6.更新pg_class中的统计信息
7.收尾工作
/*
* heap_vacuum_rel() -- perform VACUUM for one heap relation
* heap_vacuum_rel() -- 为heap relation执行VACUUM
*
* This routine vacuums a single heap, cleans out its indexes, and
* updates its relpages and reltuples statistics.
* 该处理过程vacuum一个单独的heap,清除索引并更新relpages和reltuples统计信息.
*
* At entry, we have already established a transaction and opened
* and locked the relation.
* 在该调用入口,我们已经给创建了事务并且已经打开&锁定了relation.
*/
void
heap_vacuum_rel(Relation onerel, int options, VacuumParams *params,
BufferAccessStrategy bstrategy)
{
LVRelStats *vacrelstats;//统计信息
Relation *Irel;//关系指针
int nindexes;
PGRUsage ru0;//状态结构体
TimestampTz starttime = 0;//时间戳
long secs;//秒数
int usecs;//微秒数
double read_rate,//读比率
write_rate;//写比率
//是否扫描所有未冻结的pages?
bool aggressive; /* should we scan all unfrozen pages? */
//实际上是否扫描了所有这样的pages?
bool scanned_all_unfrozen; /* actually scanned all such pages? */
TransactionId xidFullScanLimit;
MultiXactId mxactFullScanLimit;
BlockNumber new_rel_pages;
BlockNumber new_rel_allvisible;
double new_live_tuples;
TransactionId new_frozen_xid;
MultiXactId new_min_multi;
Assert(params != NULL);
/* measure elapsed time iff autovacuum logging requires it */
//如autovacuum日志记录需要,则测量耗费的时间
if (IsAutoVacuumWorkerProcess() && params->log_min_duration >= 0)
{
pg_rusage_init(&ru0);
starttime = GetCurrentTimestamp();
}
if (options & VACOPT_VERBOSE)
//需要VERBOSE
elevel = INFO;
else
elevel = DEBUG2;
pgstat_progress_start_command(PROGRESS_COMMAND_VACUUM,
RelationGetRelid(onerel));
vac_strategy = bstrategy;
//计算最老的xmin和冻结截止点
//输出:OldestXmin/FreezeLimit/FreezeLimit/MultiXactCutoff/mxactFullScanLimit
vacuum_set_xid_limits(onerel,
params->freeze_min_age,
params->freeze_table_age,
params->multixact_freeze_min_age,
params->multixact_freeze_table_age,
&OldestXmin, &FreezeLimit, &xidFullScanLimit,
&MultiXactCutoff, &mxactFullScanLimit);
/*
* We request an aggressive scan if the table's frozen Xid is now older
* than or equal to the requested Xid full-table scan limit; or if the
* table's minimum MultiXactId is older than or equal to the requested
* mxid full-table scan limit; or if DISABLE_PAGE_SKIPPING was specified.
* 如果表的frozen Xid现在大于或等于请求的Xid全表扫描限制，则请求进行主动扫描;
* 或者如果表的最小MultiXactId大于或等于请求的mxid全表扫描限制;
* 或者，如果指定了disable_page_skip。
*/
//比较onerel->rd_rel->relfrozenxid & xidFullScanLimit
//如小于等于,则aggressive为T,否则为F
aggressive = TransactionIdPrecedesOrEquals(onerel->rd_rel->relfrozenxid,
xidFullScanLimit);
//比较onerel->rd_rel->relminmxid &mxactFullScanLimit
//如小于等于,则aggressive为T
//否则aggressive原值为T,则为T,否则为F
aggressive |= MultiXactIdPrecedesOrEquals(onerel->rd_rel->relminmxid,
mxactFullScanLimit);
if (options & VACOPT_DISABLE_PAGE_SKIPPING)
//禁用跳过页,则强制为T
aggressive = true;
//分配统计结构体内存
vacrelstats = (LVRelStats *) palloc0(sizeof(LVRelStats));
//记录统计信息
vacrelstats->old_rel_pages = onerel->rd_rel->relpages;
vacrelstats->old_live_tuples = onerel->rd_rel->reltuples;
vacrelstats->num_index_scans = 0;
vacrelstats->pages_removed = 0;
vacrelstats->lock_waiter_detected = false;
/* Open all indexes of the relation */
//打开该relation所有的索引
vac_open_indexes(onerel, RowExclusiveLock, &nindexes, &Irel);
vacrelstats->hasindex = (nindexes > 0);
/* Do the vacuuming */
//执行vacuuming
lazy_scan_heap(onerel, options, vacrelstats, Irel, nindexes, aggressive);
/* Done with indexes */
//已完成index的处理
vac_close_indexes(nindexes, Irel, NoLock);
/*
* Compute whether we actually scanned the all unfrozen pages. If we did,
* we can adjust relfrozenxid and relminmxid.
* 计算我们实际上是否扫描了所有unfrozen pages.
* 如果扫描了,则需要调整relfrozenxid和relminmxid.
*
* NB: We need to check this before truncating the relation, because that
* will change ->rel_pages.
* 注意:我们需要在截断relation前执行检查,因为这会改变rel_pages.
*/
if ((vacrelstats->scanned_pages + vacrelstats->frozenskipped_pages)
< vacrelstats->rel_pages)
{
Assert(!aggressive);
scanned_all_unfrozen = false;
}
else
//扫描pages + 冻结跳过的pages >= 总pages,则为T
scanned_all_unfrozen = true;
/*
* Optionally truncate the relation.
* 可选的,截断relation
*/
if (should_attempt_truncation(vacrelstats))
lazy_truncate_heap(onerel, vacrelstats);
/* Report that we are now doing final cleanup */
//通知其他进程,正在进行最后的清理
pgstat_progress_update_param(PROGRESS_VACUUM_PHASE,
PROGRESS_VACUUM_PHASE_FINAL_CLEANUP);
/*
* Update statistics in pg_class.
* 更新pg_class中的统计信息.
*
* A corner case here is that if we scanned no pages at all because every
* page is all-visible, we should not update relpages/reltuples, because
* we have no new information to contribute. In particular this keeps us
* from replacing relpages=reltuples=0 (which means "unknown tuple
* density") with nonzero relpages and reltuples=0 (which means "zero
* tuple density") unless there's some actual evidence for the latter.
* 这里的一个极端情况是，如果每个页面都是可见的，这时候根本没有扫描任何页面，
* 那么就不应该更新relpages/reltuples，因为我们没有新信息可以更新。
* 特别地，这阻止我们将relpages=reltuple =0(这意味着“未知的元组密度”)替换
* 为非零relpages和reltuple=0(这意味着“零元组密度”)，
* 除非有关于后者的一些实际的证据。
*
* It's important that we use tupcount_pages and not scanned_pages for the
* check described above; scanned_pages counts pages where we could not
* get cleanup lock, and which were processed only for frozenxid purposes.
* 对于上面描述的检查，使用tupcount_pages而不是scanned_pages是很重要的;
* scanned_pages对无法获得清理锁的页面进行计数，这些页面仅用于frozenxid目的。
*
* We do update relallvisible even in the corner case, since if the table
* is all-visible we'd definitely like to know that. But clamp the value
* to be not more than what we're setting relpages to.
* 即使在极端情况下,我们也会更新relallvisible,因为如果表是all-visible的,那我们肯定想知道这个.
* 但是不要超过我们设置relpages的值。
*
* Also, don't change relfrozenxid/relminmxid if we skipped any pages,
* since then we don't know for certain that all tuples have a newer xmin.
* 同时,如果我们跳过了所有的页面,不能更新relfrozenxid/relminmxid,
* 因为从那时起,我们不能确定所有元组是否都有更新的xmin.
*/
new_rel_pages = vacrelstats->rel_pages;
new_live_tuples = vacrelstats->new_live_tuples;
if (vacrelstats->tupcount_pages == 0 && new_rel_pages > 0)
{
//实际处理的tuple为0而且总页面不为0,则调整回原页数
new_rel_pages = vacrelstats->old_rel_pages;
new_live_tuples = vacrelstats->old_live_tuples;
}
visibilitymap_count(onerel, &new_rel_allvisible, NULL);
if (new_rel_allvisible > new_rel_pages)
new_rel_allvisible = new_rel_pages;
new_frozen_xid = scanned_all_unfrozen ? FreezeLimit : InvalidTransactionId;
new_min_multi = scanned_all_unfrozen ? MultiXactCutoff : InvalidMultiXactId;
//更新pg_class中的统计信息
vac_update_relstats(onerel,
new_rel_pages,
new_live_tuples,
new_rel_allvisible,
vacrelstats->hasindex,
new_frozen_xid,
new_min_multi,
false);
/* report results to the stats collector, too */
//同时,发送结果给统计收集器
pgstat_report_vacuum(RelationGetRelid(onerel),
onerel->rd_rel->relisshared,
new_live_tuples,
vacrelstats->new_dead_tuples);
pgstat_progress_end_command();
/* and log the action if appropriate */
//并在适当的情况下记录操作
if (IsAutoVacuumWorkerProcess() && params->log_min_duration >= 0)
{
//autovacuum && 参数log_min_duration >= 0
TimestampTz endtime = GetCurrentTimestamp();
if (params->log_min_duration == 0 ||
TimestampDifferenceExceeds(starttime, endtime,
params->log_min_duration))
{
StringInfoData buf;
char *msgfmt;
TimestampDifference(starttime, endtime, &secs, &usecs);
read_rate = 0;
write_rate = 0;
if ((secs > 0) || (usecs > 0))
{
read_rate = (double) BLCKSZ * VacuumPageMiss / (1024 * 1024) /
(secs + usecs / 1000000.0);
write_rate = (double) BLCKSZ * VacuumPageDirty / (1024 * 1024) /
(secs + usecs / 1000000.0);
}
/*
* This is pretty messy, but we split it up so that we can skip
* emitting individual parts of the message when not applicable.
*/
initStringInfo(&buf);
if (params->is_wraparound)
{
if (aggressive)
msgfmt = _("automatic aggressive vacuum to prevent wraparound of table \"%s.%s.%s\": index scans: %d\n");
else
msgfmt = _("automatic vacuum to prevent wraparound of table \"%s.%s.%s\": index scans: %d\n");
}
else
{
if (aggressive)
msgfmt = _("automatic aggressive vacuum of table \"%s.%s.%s\": index scans: %d\n");
else
msgfmt = _("automatic vacuum of table \"%s.%s.%s\": index scans: %d\n");
}
appendStringInfo(&buf, msgfmt,
get_database_name(MyDatabaseId),
get_namespace_name(RelationGetNamespace(onerel)),
RelationGetRelationName(onerel),
vacrelstats->num_index_scans);
appendStringInfo(&buf, _("pages: %u removed, %u remain, %u skipped due to pins, %u skipped frozen\n"),
vacrelstats->pages_removed,
vacrelstats->rel_pages,
vacrelstats->pinskipped_pages,
vacrelstats->frozenskipped_pages);
appendStringInfo(&buf,
_("tuples: %.0f removed, %.0f remain, %.0f are dead but not yet removable, oldest xmin: %u\n"),
vacrelstats->tuples_deleted,
vacrelstats->new_rel_tuples,
vacrelstats->new_dead_tuples,
OldestXmin);
appendStringInfo(&buf,
_("buffer usage: %d hits, %d misses, %d dirtied\n"),
VacuumPageHit,
VacuumPageMiss,
VacuumPageDirty);
appendStringInfo(&buf, _("avg read rate: %.3f MB/s, avg write rate: %.3f MB/s\n"),
read_rate, write_rate);
appendStringInfo(&buf, _("system usage: %s"), pg_rusage_show(&ru0));
ereport(LOG,
(errmsg_internal("%s", buf.data)));
pfree(buf.data);
}
}
}三、跟踪分析
测试脚本
11:45:37 (xdb@[local]:5432)testdb=# vacuum t1;
启动gdb,设置断点
注:PG主线函数名称已改为heap_vacuum_rel,PG 11.1仍为lazy_vacuum_rel
(gdb) c Continuing. Breakpoint 1, lazy_vacuum_rel (onerel=0x7f226cd9e9a0, options=1, params=0x7ffe010d5b70, bstrategy=0x1da9708) at vacuumlazy.c:197 197 TimestampTz starttime = 0; (gdb)
输入参数
relation
(gdb) p *onerel
$1 = {rd_node = {spcNode = 1663, dbNode = 16402, relNode = 50820}, rd_smgr = 0x0, rd_refcnt = 1, rd_backend = -1,
rd_islocaltemp = false, rd_isnailed = false, rd_isvalid = true, rd_indexvalid = 0 '\000', rd_statvalid = false,
rd_createSubid = 0, rd_newRelfilenodeSubid = 0, rd_rel = 0x7f226cd9ebb8, rd_att = 0x7f226cd9ecd0, rd_id = 50820,
rd_lockInfo = {lockRelId = {relId = 50820, dbId = 16402}}, rd_rules = 0x0, rd_rulescxt = 0x0, trigdesc = 0x0,
rd_rsdesc = 0x0, rd_fkeylist = 0x0, rd_fkeyvalid = false, rd_partkeycxt = 0x0, rd_partkey = 0x0, rd_pdcxt = 0x0,
rd_partdesc = 0x0, rd_partcheck = 0x0, rd_indexlist = 0x0, rd_oidindex = 0, rd_pkindex = 0, rd_replidindex = 0,
rd_statlist = 0x0, rd_indexattr = 0x0, rd_projindexattr = 0x0, rd_keyattr = 0x0, rd_pkattr = 0x0, rd_idattr = 0x0,
rd_projidx = 0x0, rd_pubactions = 0x0, rd_options = 0x0, rd_index = 0x0, rd_indextuple = 0x0, rd_amhandler = 0,
rd_indexcxt = 0x0, rd_amroutine = 0x0, rd_opfamily = 0x0, rd_opcintype = 0x0, rd_support = 0x0, rd_supportinfo = 0x0,
rd_indoption = 0x0, rd_indexprs = 0x0, rd_indpred = 0x0, rd_exclops = 0x0, rd_exclprocs = 0x0, rd_exclstrats = 0x0,
rd_amcache = 0x0, rd_indcollation = 0x0, rd_fdwroutine = 0x0, rd_toastoid = 0, pgstat_info = 0x1d5a030}
(gdb)vacuum参数
(gdb) p *params
$2 = {freeze_min_age = -1, freeze_table_age = -1, multixact_freeze_min_age = -1, multixact_freeze_table_age = -1,
is_wraparound = false, log_min_duration = -1}
(gdb)buffer访问策略对象
(gdb) p *bstrategy
$3 = {btype = BAS_VACUUM, ring_size = 32, current = 0, current_was_in_ring = false, buffers = 0x1da9718}
(gdb)
(gdb) p *bstrategy->buffers
$4 = 0
(gdb)1.初始化相关变量,如本地变量/日志记录级别/访问策略等
$4 = 0 (gdb) n 215 if (IsAutoVacuumWorkerProcess() && params->log_min_duration >= 0) (gdb) 221 if (options & VACOPT_VERBOSE) (gdb) 224 elevel = DEBUG2; (gdb) 226 pgstat_progress_start_command(PROGRESS_COMMAND_VACUUM, (gdb) 229 vac_strategy = bstrategy; (gdb)
2.调用vacuum_set_xid_limits计算最老的xmin和冻结截止点
返回值均为默认值,其中OldestXmin是当前最小的活动事务ID
231 vacuum_set_xid_limits(onerel, (gdb) 245 aggressive = TransactionIdPrecedesOrEquals(onerel->rd_rel->relfrozenxid, (gdb) p OldestXmin $5 = 307590 (gdb) p FreezeLimit $6 = 4245274886 (gdb) p xidFullScanLimit $10 = 4145274886 (gdb) p MultiXactCutoff $8 = 4289967297 (gdb) p mxactFullScanLimit $9 = 4144967297 (gdb)
3.判断是否执行全表(不跳过pages)扫描,标记变量为aggressive,值为F
(gdb) n 247 aggressive |= MultiXactIdPrecedesOrEquals(onerel->rd_rel->relminmxid, (gdb) p aggressive $11 = false (gdb) n 249 if (options & VACOPT_DISABLE_PAGE_SKIPPING) (gdb) p onerel->rd_rel->relfrozenxid $12 = 144983 (gdb) p xidFullScanLimit $13 = 4145274886 (gdb)
4.初始化统计信息结构体vacrelstats
(gdb) n
252 vacrelstats = (LVRelStats *) palloc0(sizeof(LVRelStats));
(gdb)
254 vacrelstats->old_rel_pages = onerel->rd_rel->relpages;
(gdb)
255 vacrelstats->old_live_tuples = onerel->rd_rel->reltuples;
(gdb)
256 vacrelstats->num_index_scans = 0;
(gdb)
257 vacrelstats->pages_removed = 0;
(gdb)
258 vacrelstats->lock_waiter_detected = false;
(gdb)
261 vac_open_indexes(onerel, RowExclusiveLock, &nindexes, &Irel);
(gdb) p *vacrelstats
$14 = {hasindex = false, old_rel_pages = 75, rel_pages = 0, scanned_pages = 0, pinskipped_pages = 0,
frozenskipped_pages = 0, tupcount_pages = 0, old_live_tuples = 10000, new_rel_tuples = 0, new_live_tuples = 0,
new_dead_tuples = 0, pages_removed = 0, tuples_deleted = 0, nonempty_pages = 0, num_dead_tuples = 0, max_dead_tuples = 0,
dead_tuples = 0x0, num_index_scans = 0, latestRemovedXid = 0, lock_waiter_detected = false}
(gdb)5.打开索引,执行函数lazy_scan_heap进行vacuuming,关闭索引
(gdb) n
262 vacrelstats->hasindex = (nindexes > 0);
(gdb)
265 lazy_scan_heap(onerel, options, vacrelstats, Irel, nindexes, aggressive);
(gdb)
268 vac_close_indexes(nindexes, Irel, NoLock);
(gdb)
(gdb)
277 if ((vacrelstats->scanned_pages + vacrelstats->frozenskipped_pages)
(gdb)
278 < vacrelstats->rel_pages)
(gdb)
277 if ((vacrelstats->scanned_pages + vacrelstats->frozenskipped_pages)
(gdb)
284 scanned_all_unfrozen = true;
(gdb) p *vacrelstats
$15 = {hasindex = true, old_rel_pages = 75, rel_pages = 75, scanned_pages = 75, pinskipped_pages = 0,
frozenskipped_pages = 0, tupcount_pages = 75, old_live_tuples = 10000, new_rel_tuples = 10154, new_live_tuples = 10000,
new_dead_tuples = 154, pages_removed = 0, tuples_deleted = 0, nonempty_pages = 75, num_dead_tuples = 0,
max_dead_tuples = 21825, dead_tuples = 0x1db5030, num_index_scans = 0, latestRemovedXid = 0, lock_waiter_detected = false}
(gdb) p vacrelstats->scanned_pages
$16 = 75
(gdb) p vacrelstats->frozenskipped_pages
$17 = 0
(gdb) p vacrelstats->rel_pages
$18 = 75
(gdb)6.更新pg_class中的统计信息
(gdb) n 289 if (should_attempt_truncation(vacrelstats)) (gdb) 293 pgstat_progress_update_param(PROGRESS_VACUUM_PHASE, (gdb) 317 new_rel_pages = vacrelstats->rel_pages; (gdb) 318 new_live_tuples = vacrelstats->new_live_tuples; (gdb) 319 if (vacrelstats->tupcount_pages == 0 && new_rel_pages > 0) (gdb) 325 visibilitymap_count(onerel, &new_rel_allvisible, NULL); (gdb) 326 if (new_rel_allvisible > new_rel_pages) (gdb) p new_rel_allvisible $19 = 0 (gdb) p new_rel_pages $20 = 75 (gdb) n 329 new_frozen_xid = scanned_all_unfrozen ? FreezeLimit : InvalidTransactionId; (gdb) 330 new_min_multi = scanned_all_unfrozen ? MultiXactCutoff : InvalidMultiXactId; (gdb) 336 vacrelstats->hasindex, (gdb) 332 vac_update_relstats(onerel, (gdb) p new_frozen_xid $21 = 4245274886 (gdb) p new_min_multi $22 = 4289967297 (gdb)
7.收尾工作
(gdb) n 345 vacrelstats->new_dead_tuples); (gdb) 342 pgstat_report_vacuum(RelationGetRelid(onerel), (gdb) 343 onerel->rd_rel->relisshared, (gdb) 342 pgstat_report_vacuum(RelationGetRelid(onerel), (gdb) 346 pgstat_progress_end_command(); (gdb) 349 if (IsAutoVacuumWorkerProcess() && params->log_min_duration >= 0) (gdb)
完成调用
411 } (gdb) vacuum_rel (relid=50820, relation=0x1cdb8d0, options=1, params=0x7ffe010d5b70) at vacuum.c:1560 1560 AtEOXact_GUC(false, save_nestlevel); (gdb)
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文章标题：PostgreSQL的vacuum过程中heap_vacuum_rel函数分析
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