相同SQL在不同實(shí)例結(jié)果竟然不同，你知道嗎？
作者：胖頭魚(yú)的魚(yú)缸
這是一個(gè)遺留的老庫(kù)，4節(jié)點(diǎn)12.2的RAC。我們每天都會(huì)通過(guò)EM對(duì)數(shù)據(jù)庫(kù)所有PDB的表空間使用量進(jìn)行巡檢，針對(duì)使用率較高的表空間將和業(yè)務(wù)方進(jìn)行溝通并擴(kuò)容。
1 問(wèn)題背景
這是一個(gè)遺留的老庫(kù)，4節(jié)點(diǎn)12.2的RAC。我們每天都會(huì)通過(guò)EM對(duì)數(shù)據(jù)庫(kù)所有PDB的表空間使用量進(jìn)行巡檢，針對(duì)使用率較高的表空間將和業(yè)務(wù)方進(jìn)行溝通并擴(kuò)容。但是最近發(fā)現(xiàn)一個(gè)非常奇怪的現(xiàn)象，即根據(jù)表空間當(dāng)前使用數(shù)據(jù)量和數(shù)據(jù)文件自動(dòng)增長(zhǎng)的最大值比值得出的已用空間使用率（Available Space Used(%)）沒(méi)有產(chǎn)生變化了，但是其余的值比如已用的分配空間占用率（Allocated Space Used (%)）、分配大小（Allocated Size (GB)）、已用空間（Space Used(GB)）、數(shù)據(jù)文件數(shù)量（Datafiles）等其他數(shù)據(jù)卻又是變化的，且可以通過(guò)這些數(shù)值又可以人工算出正確的已用空間使用率結(jié)果：而奇怪的是，進(jìn)入PDB中又會(huì)發(fā)現(xiàn)已用用空間使用率結(jié)果是正確的。
2 前期排查
其實(shí)這個(gè)頁(yè)面的后臺(tái)語(yǔ)句。
select * from (
WITH df AS (
SELECT
con_id,
tablespace_name,
SUM(bytes) bytes,
COUNT(*) cnt,
DECODE(SUM(DECODE(autoextensible, 'NO', 0, 1)), 0, 'NO', 'YES') autoext
FROM
cdb_data_files
GROUPBY
con_id,
tablespace_name),
um AS (SELECT con_id, tablespace_name, used_space ub, used_percent FROM cdb_tablespace_usage_metrics),
pdb AS (SELECT con_id, NAMEFROM v$containers) SELECT
p.NAME,
d.tablespace_name,
TO_CHAR (u.used_percent, '99999990.00'),
NVL ((a.bytes - NVL (f.bytes, 0)) / a.bytes * 100, 0),
a.autoext,
NVL (a.bytes, 0) / 1024 / 1024 / 1024,
NVL (a.bytes - NVL (f.bytes, 0), 0) / 1024 / 1024 / 1024,
NVL (f.bytes, 0) / 1024 / 1024 / 1024,
d.STATUS,
a.cnt,
d.contents,
d.extent_management,
d.segment_space_management
FROM
cdb_tablespaces d,
df a,
um u,
pdb p,
(SELECT CON_ID, tablespace_name, SUM(bytes) bytesFROM cdb_free_space GROUPBY CON_ID, tablespace_name) f
WHERE
d.tablespace_name = a.tablespace_name (+)
AND d.tablespace_name = f.tablespace_name (+)
AND d.tablespace_name = u.tablespace_name (+)
ANDNOT d.contents = 'UNDO'
ANDNOT (d.extent_management = 'LOCAL'AND d.contents = 'TEMPORARY')
AND p.con_id = d.con_id
AND p.con_id = u.con_id (+)
AND p.con_id = a.con_id (+)
AND p.con_id = f.con_id (+) UNIONALL
SELECT p.NAME,
d.tablespace_name,
TO_CHAR (u.used_percent, '99999990.00'),
NVL ((u.ub * d.block_size) / tf.bytes * 100, 0),
tf.autoext,
NVL (tf.bytes, 0) / 1024 / 1024 / 1024,
NVL (u.ub * d.block_size, 0) / 1024 / 1024 / 1024,
(NVL (tf.bytes, 0) - NVL (u.ub * d.block_size, 0)) / 1024 / 1024 / 1024,
d.STATUS,
tf.cnt,
d.contents,
d.extent_management,
d.segment_space_management
FROM
cdb_tablespaces d,
um u,
pdb p,
(
SELECT
con_id,
tablespace_name,
SUM(bytes) bytes,
COUNT(*) cnt,
DECODE(SUM(DECODE(autoextensible, 'NO', 0, 1)), 0, 'NO', 'YES') autoext
FROM
cdb_temp_files
GROUPBY
con_id,
tablespace_name) tf
WHERE
d.tablespace_name = tf.tablespace_name (+)
AND d.tablespace_name = u.tablespace_name (+)
AND d.extent_management = 'LOCAL'
AND d.contents = 'TEMPORARY'
AND p.con_id = d.con_id
AND p.con_id = u.con_id (+)
AND p.con_id = tf.con_id (+) UNIONALL
SELECT
p.NAME,
d.tablespace_name,
TO_CHAR (u.used_percent, '99999990.00'),
NVL ((u.ub * d.block_size) / a.bytes * 100, 0),
a.autoext,
NVL (a.bytes, 0) / 1024 / 1024 / 1024,
NVL (u.ub * d.block_size, 0) / 1024 / 1024 / 1024,
(NVL (a.bytes, 0) - NVL (u.ub * d.block_size, 0)) / 1024 / 1024 / 1024,
d.STATUS,
a.cnt,
d.contents,
d.extent_management,
d.segment_space_management
FROM
cdb_tablespaces d,
df a,
um u,
pdb p
WHERE
d.tablespace_name = a.tablespace_name (+)
AND d.tablespace_name = u.tablespace_name (+)
AND d.contents = 'UNDO'
AND p.con_id = d.con_id
AND p.con_id = u.con_id (+)
AND p.con_id = a.con_id (+)
) orderby3;這里在外面嵌套了一層用于排序。因?yàn)橛?jì)算結(jié)果沒(méi)有更新，一開(kāi)始的排查方向是EM的緩存沒(méi)有清理，但是對(duì)EM的各項(xiàng)設(shè)置進(jìn)行檢查后，并沒(méi)有發(fā)現(xiàn)相關(guān)問(wèn)題。隨即在各個(gè)節(jié)點(diǎn)上執(zhí)行該SQL，發(fā)現(xiàn)在節(jié)點(diǎn)1上執(zhí)行結(jié)果有問(wèn)題，在EM上將表空間查詢操作指定到其他實(shí)例結(jié)果也是正確的。隨即又開(kāi)了個(gè)和數(shù)據(jù)庫(kù)相關(guān)的SR。
3 深入排查
在數(shù)據(jù)庫(kù)SR的指引下，收集了SQLHC的相關(guān)診斷信息，然后給了一大堆hint：
select
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('12.2.0.1')
DB_VERSION('12.2.0.1')
ALL_ROWS
OUTLINE_LEAF(@"SEL$07BDC5B4")
MERGE(@"SEL$4" >"SEL$3")
OUTLINE_LEAF(@"SEL$ABDE6DFF")
MERGE(@"SEL$6" >"SEL$5")
OUTLINE_LEAF(@"SEL$DFD66ADD")
MERGE(@"SEL$CF5359D5" >"SEL$7")
OUTLINE_LEAF(@"SEL$22C746FF")
OUTLINE_LEAF(@"SEL$513E9771")
OUTLINE_LEAF(@"SEL$522E92D8")
OUTLINE_LEAF(@"SEL$42DFC41A")
MERGE(@"SEL$12" >"SEL$11")
OUTLINE_LEAF(@"SEL$1F78930A")
MERGE(@"SEL$10" >"SEL$2")
OUTLINE_LEAF(@"SEL$513E9770")
OUTLINE_LEAF(@"SEL$522E92D7")
OUTLINE_LEAF(@"SEL$29F99543")
MERGE(@"SEL$16" >"SEL$15")
OUTLINE_LEAF(@"SEL$1CF66C63")
MERGE(@"SEL$14" >"SEL$13")
OUTLINE_LEAF(@"SEL$22C746FE")
MATERIALIZE(@"SEL$07BDC5B4")
OUTLINE_LEAF(@"SEL$513E976F")
MATERIALIZE(@"SEL$ABDE6DFF")
OUTLINE_LEAF(@"SEL$522E92D6")
MATERIALIZE(@"SEL$DFD66ADD")
OUTLINE_LEAF(@"SEL$DC4B4145")
MERGE(@"SEL$18" >"SEL$17")
OUTLINE_LEAF(@"SET$1")
OUTLINE_LEAF(@"SEL$1")
OUTLINE(@"SEL$3")
OUTLINE(@"SEL$4")
OUTLINE(@"SEL$5")
OUTLINE(@"SEL$6")
OUTLINE(@"SEL$7")
OUTLINE(@"SEL$CF5359D5")
MERGE(@"SEL$9" >"SEL$8")
OUTLINE(@"SEL$07BDC5B4")
MERGE(@"SEL$4" >"SEL$3")
OUTLINE(@"SEL$ABDE6DFF")
MERGE(@"SEL$6" >"SEL$5")
OUTLINE(@"SEL$DFD66ADD")
MERGE(@"SEL$CF5359D5" >"SEL$7")
OUTLINE(@"SEL$11")
OUTLINE(@"SEL$12")
OUTLINE(@"SEL$2")
OUTLINE(@"SEL$10")
OUTLINE(@"SEL$15")
OUTLINE(@"SEL$16")
OUTLINE(@"SEL$13")
OUTLINE(@"SEL$14")
OUTLINE(@"SEL$17")
OUTLINE(@"SEL$18")
OUTLINE(@"SEL$8")
OUTLINE(@"SEL$9")
NO_ACCESS(@"SEL$1" "from$_subquery$_001"@"SEL$1")
PQ_CONCURRENT_UNION(@"SET$1")
NO_ACCESS(@"SEL$DC4B4145" "P"@"SEL$17")
FULL(@"SEL$DC4B4145" "K"@"SEL$18")
NO_ACCESS(@"SEL$DC4B4145" "A"@"SEL$17")
NO_ACCESS(@"SEL$DC4B4145" "U"@"SEL$17")
LEADING(@"SEL$DC4B4145" "P"@"SEL$17" "K"@"SEL$18" "A"@"SEL$17" "U"@"SEL$17")
USE_HASH(@"SEL$DC4B4145" "K"@"SEL$18")
USE_HASH(@"SEL$DC4B4145" "A"@"SEL$17")
USE_HASH(@"SEL$DC4B4145" "U"@"SEL$17")
PQ_DISTRIBUTE(@"SEL$DC4B4145" "K"@"SEL$18" HASH HASH)
PQ_DISTRIBUTE(@"SEL$DC4B4145" "A"@"SEL$17" HASH HASH)
PQ_DISTRIBUTE(@"SEL$DC4B4145" "U"@"SEL$17" HASH HASH)
NO_ACCESS(@"SEL$1CF66C63" "P"@"SEL$13")
FULL(@"SEL$1CF66C63" "K"@"SEL$14")
NO_ACCESS(@"SEL$1CF66C63" "U"@"SEL$13")
NO_ACCESS(@"SEL$1CF66C63" "TF"@"SEL$13")
LEADING(@"SEL$1CF66C63" "P"@"SEL$13" "K"@"SEL$14" "U"@"SEL$13" "TF"@"SEL$13")
USE_HASH(@"SEL$1CF66C63" "K"@"SEL$14")
USE_HASH(@"SEL$1CF66C63" "U"@"SEL$13")
USE_HASH(@"SEL$1CF66C63" "TF"@"SEL$13")
PQ_DISTRIBUTE(@"SEL$1CF66C63" "K"@"SEL$14" HASH HASH)
PQ_DISTRIBUTE(@"SEL$1CF66C63" "U"@"SEL$13" HASH HASH)
PQ_DISTRIBUTE(@"SEL$1CF66C63" "TF"@"SEL$13" HASH HASH)
PX_JOIN_FILTER(@"SEL$1CF66C63" "TF"@"SEL$13")
NO_ACCESS(@"SEL$1F78930A" "P"@"SEL$2")
FULL(@"SEL$1F78930A" "K"@"SEL$10")
NO_ACCESS(@"SEL$1F78930A" "A"@"SEL$2")
NO_ACCESS(@"SEL$1F78930A" "U"@"SEL$2")
NO_ACCESS(@"SEL$1F78930A" "F"@"SEL$2")
LEADING(@"SEL$1F78930A" "P"@"SEL$2" "K"@"SEL$10" "A"@"SEL$2" "U"@"SEL$2" "F"@"SEL$2")
USE_HASH(@"SEL$1F78930A" "K"@"SEL$10")
USE_HASH(@"SEL$1F78930A" "A"@"SEL$2")
USE_HASH(@"SEL$1F78930A" "U"@"SEL$2")
USE_HASH(@"SEL$1F78930A" "F"@"SEL$2")
PQ_DISTRIBUTE(@"SEL$1F78930A" "K"@"SEL$10" HASH HASH)
PQ_DISTRIBUTE(@"SEL$1F78930A" "A"@"SEL$2" HASH HASH)
PQ_DISTRIBUTE(@"SEL$1F78930A" "U"@"SEL$2" HASH HASH)
PQ_DISTRIBUTE(@"SEL$1F78930A" "F"@"SEL$2" HASH HASH)
PX_JOIN_FILTER(@"SEL$1F78930A" "F"@"SEL$2")
FULL(@"SEL$522E92D8" "T1"@"SEL$522E92D8")
FULL(@"SEL$513E9771" "T1"@"SEL$513E9771")
FULL(@"SEL$22C746FF" "T1"@"SEL$22C746FF")
FULL(@"SEL$42DFC41A" "K"@"SEL$12")
GBY_PUSHDOWN(@"SEL$42DFC41A")
USE_HASH_AGGREGATION(@"SEL$42DFC41A")
FULL(@"SEL$522E92D7" "T1"@"SEL$522E92D7")
FULL(@"SEL$513E9770" "T1"@"SEL$513E9770")
FULL(@"SEL$29F99543" "K"@"SEL$16")
GBY_PUSHDOWN(@"SEL$29F99543")
USE_HASH_AGGREGATION(@"SEL$29F99543")
FULL(@"SEL$522E92D6" "T1"@"SEL$522E92D6")
FULL(@"SEL$513E976F" "T1"@"SEL$513E976F")
FULL(@"SEL$22C746FE" "T1"@"SEL$22C746FE")
FULL(@"SEL$DFD66ADD" "X$CON"@"SEL$9")
FULL(@"SEL$ABDE6DFF" "K"@"SEL$6")
FULL(@"SEL$07BDC5B4" "K"@"SEL$4")
USE_HASH_AGGREGATION(@"SEL$07BDC5B4")
USE_PARTITION_WISE_GBY(@"SEL$07BDC5B4")
END_OUTLINE_DATA
*/
* from (
WITH df AS (
SELECT
...對(duì)比不同節(jié)點(diǎn)的SQL的實(shí)際執(zhí)行計(jì)劃的Outline信息（這里不做展示），這里是通過(guò)hint的方式SQL執(zhí)行將指向到正確的執(zhí)行計(jì)劃，輸出結(jié)果也回歸正常。SR的回復(fù)則是：
實(shí)例 1 hard parse 出來(lái)的執(zhí)行計(jì)劃產(chǎn)生了錯(cuò)誤結(jié)果，這個(gè)執(zhí)行計(jì)劃可能是一個(gè)不正確的執(zhí)行計(jì)劃。一個(gè)錯(cuò)誤的執(zhí)行計(jì)劃有可能產(chǎn)生錯(cuò)誤的記錄條數(shù)，也可能產(chǎn)生正確的結(jié)果條數(shù)，但是每個(gè)記錄中的 sum / count 數(shù)據(jù)項(xiàng)卻不正確。這都是錯(cuò)誤執(zhí)行計(jì)劃可能導(dǎo)致的結(jié)果。
4 嘗試解決
既然執(zhí)行計(jì)劃有誤，SQL PLAN會(huì)緩存在Shared Pool中，那么是不是可以通過(guò)清理Shared Pool的執(zhí)行計(jì)劃緩存來(lái)解決這一問(wèn)題呢：
-- 查詢語(yǔ)句的相關(guān)信息
SELECT sql_text, plan_hash_value, address, hash_value
FROM v$sqlarea
WHERE sql_id = '1fr0p0hnav1bq';-- 清理執(zhí)行計(jì)劃緩存
-- EXEC DBMS_SHARED_POOL.PURGE('ADDRESS,HASH_VALUE', 'C');
EXEC DBMS_SHARED_POOL.PURGE('0000000A32100428,682460534', 'C');再次查詢，結(jié)果恢復(fù)正常：目前得到的消息，這一現(xiàn)象僅會(huì)出現(xiàn)在對(duì)系統(tǒng)視圖、元數(shù)據(jù)的復(fù)雜查詢中。將對(duì)應(yīng)幾條語(yǔ)句的執(zhí)行計(jì)劃緩存都清理過(guò)后，直接執(zhí)行語(yǔ)句沒(méi)問(wèn)題了，但EM顯示還是有點(diǎn)問(wèn)題，相關(guān)問(wèn)題還得繼續(xù)處理。
總結(jié)
這是一個(gè)比較奇怪的從EM中發(fā)現(xiàn)的現(xiàn)象，目前已解決了數(shù)據(jù)庫(kù)層面的問(wèn)題。
責(zé)任編輯：武曉燕
來(lái)源：
胖頭魚(yú)的魚(yú)缸
