lsn mysql_mysql源码片段 innodb启动checkpoint flush脏页 lsn几个关键点检查过程整理「建议收藏」

mysql innodb引擎如何判断进程是正常停止(shutdown停止)

还是异常停止(crash 或者 被kill 或者主机宕机导致的进程停止)呢？代码是如何判断的呢

注：代码来源于mysql5.7.27

innodb 启动入口函数 innobase_start_or_create_for_mysql

调用recv_recovery_from_checkpoint_start 检查redo日志该如何启动

概括几个点

1 如果 checkpoint_lsn 与 flush_lsn 不相等 则表示mysql 非正常停止

2 checkpoint 写redo日志的检查点 recv_sys->mlog_checkpoint_lsn == 0

3 redo日志文件循环使用，启动时如何判断myql服务停止前redo日志记录的位置

详细描述

mysql 是否正常停止

判断 checkpoint_lsn 与 flush_lsn 是否相等

如果相等则正常停止

如果不相等，则非正常停止

/*

函数 recv_recovery_from_checkpoint_start

日志扫描完成后判断是否正常停止

checkpoint_lsn 为log_checkpoint 的lsn

flush_lsn 为redo日志写到磁盘的lsn，仅仅在正常停止的时候才更新

*/

文件log0recv.cc的代码片段

/*设置标志位，正式明确需要恢复redo日志*/

0358 /*******************************************************//**

0359 Initialize crash recovery environment. Can be called iff

0360 recv_needed_recovery == false. */

0361 static

0362 void

0363 recv_init_crash_recovery(void)

0364 {

0365 ut_ad(!srv_read_only_mode);

0366 ut_a(!recv_needed_recovery);

0367 /*设置标志位，说明非正常停止，需要恢复日志*/

0368 recv_needed_recovery = true;

0369 }

flush_lsn读取

函数 innobase_start_or_create_for_mysql(void)

/*读取ibdata1文件中记录第一个page FIL_PAGE_FILE_FLUSH_LSN的位置存储的 lsn*/

fsp0sysspace.cc

1934 err = srv_sys_space.open_or_create(

1935false, create_new_db, &sum_of_new_sizes, &flushed_lsn);

fsp0file.cc

561 *flush_lsn = mach_read_from_8(

562m_first_page + FIL_PAGE_FILE_FLUSH_LSN);

/*读取flushed_lsn堆栈信息*/

#0 Datafile::validate_first_page (this=0x2deb438, flush_lsn=0x7fffffff9150, for_import=false) at storage/innobase/fsp/fsp0file.cc:559

#1 0x0000000001c0931c in SysTablespace::read_lsn_and_check_flags (this=0x2d8d460 , flushed_lsn=0x7fffffff9150) at storage/innobase/fsp/fsp0sysspace.cc:580

#2 0x0000000001c0a961 in SysTablespace::open_or_create (this=0x2d8d460 , is_temp=false, create_new_db=false, sum_new_sizes=0x7fffffff9110, flush_lsn=0x7fffffff9150) at storage/innobase/fsp/fsp0sysspace.cc:935

#3 0x0000000001a9c2df in innobase_start_or_create_for_mysql () at storage/innobase/srv/srv0start.cc:1935

#4 0x00000000018c21d9 in innobase_init (p=0x2de9fc0) at storage/innobase/handler/ha_innodb.cc:4080

#5 0x0000000000f2ee02 in ha_initialize_handlerton (plugin=0x2f4db90) at sql/handler.cc:840

#6 0x0000000001568fd4 in plugin_initialize (plugin=0x2f4db90) at sql/sql_plugin.cc:1226

#7 0x0000000001569c3a in plugin_register_builtin_and_init_core_se (argc=0x2d1b050 , argv=0x2de82d8) at sql/sql_plugin.cc:1589

#8 0x0000000000ea8fdf in init_server_components () at sql/mysqld.cc:4079

#9 0x0000000000eaa5b4 in mysqld_main (argc=92, argv=0x2de82d8) at sql/mysqld.cc:4773

#10 0x0000000000ea21bd in main (argc=3, argv=0x7fffffffe4b8) at sql/main.cc:25

checkpoint_lsn 读取

在函数recv_recovery_from_checkpoint_start读取

读取第一个redo日志文件(即ib_logfile0)前2048字节(4*512)

在第一个512与第三个512位置读取最大一个lsn，即为checkpoint_lsn

代码如下

/* Look for the latest checkpoint from any of the log groups */

/*通过比较第2个512字节(512~1024)与第4个512字节(1536~2048)中存储的checkpoint lsn，读取最大值得所有内容*/

4065err = recv_find_max_checkpoint(&max_cp_group, &max_cp_field);

4066

4067if (err != DB_SUCCESS) {

4068

4069log_mutex_exit();

4070

4071return(err);

4072}

4073

4074log_group_header_read(max_cp_group, max_cp_field);

4075

4076buf = log_sys->checkpoint_buf;

4077 /*读取最大值所在的buf中，取出8字节，并转换long，获取checkpoint时的lsn，lsn通过512对齐后，得到新的lsn的起始位置，从ib_logfile(0,1…)中开始读取第一个block(512字节)redo记录，从block读取出第一个mtr起始记录，开始解析redo日志*/

4078checkpoint_lsn = mach_read_from_8(buf + LOG_CHECKPOINT_LSN);

4079checkpoint_no = mach_read_from_8(buf + LOG_CHECKPOINT_NO);

/*recv_find_max_checkpoint*/

/*

读取第2个与第4个

for (field = 512; field <= 3 * 512;field += 3 * 512 – 512)

*/

1338 for (field = LOG_CHECKPOINT_1; field <= LOG_CHECKPOINT_2;

1339 field += LOG_CHECKPOINT_2 – LOG_CHECKPOINT_1) {

1340

1341log_group_header_read(group, field);

1342

1343if (!recv_check_log_header_checksum(buf)) {

1344DBUG_PRINT(“ib_log”,

1345 (“invalid checkpoint,”

1346 ” group ” ULINTPF ” at ” ULINTPF

1347 “, checksum %x”,

1348 group->id, field,

1349 (unsigned) log_block_get_checksum(

1350 buf)));

1351continue;

1352}

1353

1354group->state = LOG_GROUP_OK;

1355 /*读取checkpoint lsn*/

1356group->lsn = mach_read_from_8(

1357buf + LOG_CHECKPOINT_LSN);

1358group->lsn_offset = mach_read_from_8(

1359buf + LOG_CHECKPOINT_OFFSET);

1360checkpoint_no = mach_read_from_8(

1361buf + LOG_CHECKPOINT_NO);

1368if (checkpoint_no >= max_no) {

1369*max_group = group;

1370*max_field = field;

1371max_no = checkpoint_no;

1372}

1373}

1374

1375group = UT_LIST_GET_NEXT(log_groups, group);

1376}

checkpoint_lsn 之后的redo日志都接解析完成后，判断checkpoint_lsn 判断与flush_lsn 是否相等

执行上述代码，判断后续流程是否恢复解析redo日志

log_checkpoint 9字节redo日志

如果在redo日志中找不到9字节checkpoint日志则报错无法正常启动，需要dba特殊处理

代码检查点为

/*

recv_sys->mlog_checkpoint_lsn

如果为0 则说明在redo日志没有找到9字节的checkpoint的redo日志的记录

如果不为0 则为checkpoint_lsn的值

如果为0 且 checkpoint_lsn又不是redo日志的最后记录(group->scanned_lsn != checkpoint_lsn)，则为异常情况

*/

4161if (recv_sys->mlog_checkpoint_lsn == 0) {

4162if (!srv_read_only_mode

4163 && group->scanned_lsn != checkpoint_lsn) {

4164ib::error() << “Ignoring the redo log due to missing”

4165″ MLOG_CHECKPOINT between the checkpoint “

4166<< checkpoint_lsn << ” and the end “

4167<< group->scanned_lsn << “.”;

4168if (srv_force_recovery < SRV_FORCE_NO_LOG_REDO) {

4169log_mutex_exit();

4170return(DB_ERROR);

4171}

4172}

4173

4174group->scanned_lsn = checkpoint_lsn;

4175rescan = false;

4176}

解析redo日志，recv_sys->mlog_checkpoint_lsn赋值的地方

log0recv.cc 中函数recv_parse_log_recs中

3182 if (single_rec) {

3224 switch (type) {

3229 case MLOG_CHECKPOINT:

3230 #if SIZE_OF_MLOG_CHECKPOINT != 1 + 8

3231 # error SIZE_OF_MLOG_CHECKPOINT != 1 + 8

3232 #endif /*从redo日志读取8字节，转换成lsn，(当时做checkpoint时的lsn)*/

3233lsn = mach_read_from_8(ptr + 1);

3234

3235DBUG_PRINT(“ib_log”,

3236 (“MLOG_CHECKPOINT(” LSN_PF “) %s at “

3237 LSN_PF,

3238 lsn,

3239 lsn != checkpoint_lsn ? “ignored”

3240 : recv_sys->mlog_checkpoint_lsn

3241 ? “reread” : “read”,

3242 recv_sys->recovered_lsn));

3243 /*lsn redo日志中去读的lsn 是否是当前的 checkpoint_lsn*/

3244if (lsn == checkpoint_lsn) {

3245if (recv_sys->mlog_checkpoint_lsn) {

3246/* At recv_reset_logs() we may

3247write a duplicate MLOG_CHECKPOINT

3248for the same checkpoint LSN. Thus

3249recv_sys->mlog_checkpoint_lsn

3250can differ from the current LSN. */

3251ut_ad(recv_sys->mlog_checkpoint_lsn

3252 <= recv_sys->recovered_lsn);

3253break;

3254}

/*把当前lsn赋值给recv_sys->mlog_checkpoint_lsn，使其不为0*/

3255recv_sys->mlog_checkpoint_lsn

3256= recv_sys->recovered_lsn;

3257}

解析redo日志终止的判断

读取redo日志的一个block(512字节)，解析12字节的头(LOG_BLOCK_HDR_DATA_LEN)，读取当前block中redo日志的长度

如果为512，则此block不为最后一个redo记录的block

如果小于512 则此block为mysql服务停止后，最后一个redo记录的block

在log0recv.cc 函数中

recv_group_scan_log_recs->recv_scan_log_recs

3595do {

/*读取当前block中redo的长度*/

3639data_len = log_block_get_data_len(log_block);

/*如果当前block中redo的长度不足512，则redo全部读取完成，则退出循环*/

3729if (data_len < OS_FILE_LOG_BLOCK_SIZE) {

3730/* Log data for this group ends here */

3731finished = true;

3732break;

3733} else {

3734log_block += OS_FILE_LOG_BLOCK_SIZE;

3735}

3736} while (log_block < buf + len);

3737 /*记录当前redo日志的最大长度*/

3738*group_scanned_lsn = scanned_lsn;