【 使用环境 】测试环境
【 OB or 其他组件 】OB
【 使用版本 】4.2
【问题描述】如何理解DISK_READS和INDEX_BLOCK_READ_CNT指标含义？
测试语句：
select /*+ INDEX(a idx2) */ * from tcustomer a where C_ACCTBAL > 9000;
其执行计划：
obclient [tpch10]> explain extended pretty_color select /*+ INDEX(a idx2) */ * from customer a where C_ACCTBAL > 9000;
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Query Plan |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| =================================================== |
| |ID|OPERATOR |NAME |EST.ROWS|EST.TIME(us)| |
| --------------------------------------------------- |
| |0 |TABLE RANGE SCAN|a(idx2)|136864 |421697 | |
| =================================================== |
| Outputs & filters: |
| ------------------------------------- |
| 0 - output([a.C_CUSTKEY(0x7f738c0404a0)], [a.C_NAME(0x7f738c040770)], [a.C_ADDRESS(0x7f738c040a40)], [a.C_NATIONKEY(0x7f738c040d10)], [a.C_PHONE(0x7f738c040fe0)], |
| [a.C_ACCTBAL(0x7f738c03f470)], [a.C_MKTSEGMENT(0x7f738c0412b0)], [a.C_COMMENT(0x7f738c041580)]), filter(nil), rowset=256 |
| access([a.C_CUSTKEY(0x7f738c0404a0)], [a.C_ACCTBAL(0x7f738c03f470)], [a.C_NAME(0x7f738c040770)], [a.C_ADDRESS(0x7f738c040a40)], [a.C_NATIONKEY(0x7f738c040d10)], |
| [a.C_PHONE(0x7f738c040fe0)], [a.C_MKTSEGMENT(0x7f738c0412b0)], [a.C_COMMENT(0x7f738c041580)]), partitions(p0) |
| is_index_back=true, is_global_index=false, |
| range_key([a.C_ACCTBAL(0x7f738c03f470)], [a.C_CUSTKEY(0x7f738c0404a0)]), range(9000,MAX ; MAX,MAX), |
| range_cond([a.C_ACCTBAL(0x7f738c03f470) > cast(9000, DECIMAL(4, 0))(0x7f738c03f9c0)(0x7f738c03ed70)]) |
| Used Hint: |
| ------------------------------------- |
| /*+ |
| |
| INDEX("a" "idx2") |
| */ |
| Qb name trace: |
| ------------------------------------- |
| stmt_id:0, stmt_type:T_EXPLAIN |
| stmt_id:1, SEL$1 |
| Outline Data: |
| ------------------------------------- |
| /*+ |
| BEGIN_OUTLINE_DATA |
| INDEX(@"SEL$1" "a"@"SEL$1" "idx2") |
| OPTIMIZER_FEATURES_ENABLE('4.0.0.0') |
| END_OUTLINE_DATA |
| */ |
| Optimization Info: |
| ------------------------------------- |
| a: |
| table_rows:1500000 |
| physical_range_rows:136864 |
| logical_range_rows:136864 |
| index_back_rows:136864 |
| output_rows:136864 |
| table_dop:1 |
| dop_method:Table DOP |
| avaiable_index_name:[idx1, idx2, customer] |
| pruned_index_name:[idx1, customer] |
| stats version:1694254801441111 |
| dynamic sampling level:0 |
| Plan Type: |
| LOCAL |
| Note: |
| Degree of Parallelisim is 1 because of table property |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
50 rows in set (0.003 sec)
其audit_sql信息：
obclient [oceanbase]> select * from oceanbase.GV$ob_sql_audit where trace_id='YB42C0A81FC9-000604DBE69F658A-0-0' \G
*************************** 1. row ***************************
SVR_IP: 192.168.31.201
SVR_PORT: 2882
REQUEST_ID: 1179463
SQL_EXEC_ID: 9955581
TRACE_ID: YB42C0A81FC9-000604DBE69F658A-0-0
SID: 3221575926
CLIENT_IP: 192.168.31.192
CLIENT_PORT: 59626
TENANT_ID: 1004
TENANT_NAME: tpch
EFFECTIVE_TENANT_ID: 1004
USER_ID: 200001
USER_NAME: root
USER_GROUP: 0
USER_CLIENT_IP: 192.168.31.192
DB_ID: 500523
DB_NAME: tpch10
SQL_ID: 5A3B2E7D76A40049D03CF6EDB4D5A292
QUERY_SQL: select /*+ INDEX(a idx2) */ * from customer a where C_ACCTBAL > 9000
PLAN_ID: 80174
AFFECTED_ROWS: 0
RETURN_ROWS: 1000
PARTITION_CNT: 2
RET_CODE: 0
QC_ID: 0
DFO_ID: 0
SQC_ID: 0
WORKER_ID: 0
EVENT: db file compact read
P1TEXT: fd
P1: 167
P2TEXT: offset
P2: 0
P3TEXT: size
P3: 0
LEVEL: 0
WAIT_CLASS_ID: 109
WAIT_CLASS#: 9
WAIT_CLASS: SYSTEM_IO
STATE: WAITED SHORT TIME
WAIT_TIME_MICRO: 379
TOTAL_WAIT_TIME_MICRO: 379
TOTAL_WAITS: 1
RPC_COUNT: 0
PLAN_TYPE: 1
IS_INNER_SQL: 0
IS_EXECUTOR_RPC: 0
IS_HIT_PLAN: 0
REQUEST_TIME: 1694349304209518
ELAPSED_TIME: 10518
NET_TIME: 0
NET_WAIT_TIME: 1
QUEUE_TIME: 5
DECODE_TIME: 0
GET_PLAN_TIME: 1847
EXECUTE_TIME: 8658
APPLICATION_WAIT_TIME: 0
CONCURRENCY_WAIT_TIME: 0
USER_IO_WAIT_TIME: 0
SCHEDULE_TIME: 0
ROW_CACHE_HIT: 0
BLOOM_FILTER_CACHE_HIT: 0
BLOCK_CACHE_HIT: 1499
DISK_READS: 1
RETRY_CNT: 0
TABLE_SCAN: 0
CONSISTENCY_LEVEL: 3
MEMSTORE_READ_ROW_COUNT: 0
SSSTORE_READ_ROW_COUNT: 2000
DATA_BLOCK_READ_CNT: 1030
DATA_BLOCK_CACHE_HIT: 1030
INDEX_BLOCK_READ_CNT: 4002
INDEX_BLOCK_CACHE_HIT: 1001
BLOCKSCAN_BLOCK_CNT: 0
BLOCKSCAN_ROW_CNT: 0
PUSHDOWN_STORAGE_FILTER_ROW_CNT: 0
REQUEST_MEMORY_USED: 2607064
EXPECTED_WORKER_COUNT: 0
USED_WORKER_COUNT: 0
SCHED_INFO: NULL
FUSE_ROW_CACHE_HIT: 0
PS_CLIENT_STMT_ID: -1
PS_INNER_STMT_ID: -1
TX_ID: 0
SNAPSHOT_VERSION: 1694349304011566925
REQUEST_TYPE: 2
IS_BATCHED_MULTI_STMT: 0
OB_TRACE_INFO: NULL
PLAN_HASH: 6634794641901061603
LOCK_FOR_READ_TIME: 0
PARAMS_VALUE:
RULE_NAME:
PARTITION_HIT: 1
TX_INTERNAL_ROUTING: 0
TX_STATE_VERSION: 0
1 row in set (0.204 sec)
从过SQL_AUDIT可以看到其中三个指标：
DISK_READS: 1
INDEX_BLOCK_READ_CNT: 4002
INDEX_BLOCK_CACHE_HIT: 1001
https://www.oceanbase.com/docs/common-oceanbase-database-cn-1000000000035692
DISK_READS:是物理读次数，
INDEX_BLOCK_READ_CNT: 访问的中间层微块数量，**如何理解这个中间层微块数量？**我理解是不是索引扫描的微块数量？
假设是索引扫描微块数量，那么INDEX_BLOCK_READ_CNT-INDEX_BLOCK_CACHE_HIT=3001个微块需要从磁盘中读取，一个微块一次IO，那么和DISK_READS的物理读次数对不上。
所以应该如何理解DISK_READS和INDEX_BLOCK_READ_CNT指标含义？