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[23기_오지송] 성능최적화 미션 제출합니다. #75

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[23기_오지송] 성능최적화 미션 제출합니다. #75

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005cbd9
fix: 로그인 트랜잭션 읽기 전용 설정 수정
Oh-Jisong May 23, 2026
b4af522
docs: 트랜잭션·인덱스 과제와 성능 실험 정리
Oh-Jisong May 23, 2026
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924 changes: 776 additions & 148 deletions README.md
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24 changes: 24 additions & 0 deletions docs/performance-logs/case1_where_index.txt
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Case 1. WHERE condition index

-- Before
mysql> EXPLAIN ANALYZE SELECT * FROM reservations WHERE member_id = 1;

@taeik21 taeik21 May 23, 2026

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Explain Analyze를 통해 실제 쿼리 실행 계획까지 보여주셨네요!!

+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Filter: (reservations.member_id = 1) (cost=10104 rows=9967) (actual time=0.328..50.8 rows=150 loops=1)
-> Table scan on reservations (cost=10104 rows=99673) (actual time=0.327..45.8 rows=100000 loops=1)
|
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

-- Apply
mysql> CREATE INDEX idx_reservations_member_id ON reservations(member_id);


-- After
mysql> EXPLAIN ANALYZE SELECT * FROM reservations WHERE member_id = 1;
+---------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+---------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Index lookup on reservations using idx_reservations_member_id (member_id=1) (cost=52.5 rows=150) (actual time=0.118..0.542 rows=150 loops=1)
|
+---------------------------------------------------------------------------------------------------------------------------------------------------+
47 changes: 47 additions & 0 deletions docs/performance-logs/case2_selective_index.txt
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Case 2. Selective index choice

-- Reset
mysql> DROP INDEX idx_reservations_member_id ON reservations;


-- Before
mysql> EXPLAIN ANALYZE SELECT * FROM reservations WHERE status = 'CONFIRMED' AND reserved_at >= DATE_SUB(NOW(), INTERVAL 3 DAY);
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Filter: ((reservations.`status` = 'CONFIRMED') and (reservations.reserved_at >= <cache>((now() - interval 3 day)))) (cost=9439 rows=3322) (actual time=0.353..75.3 rows=1427 loops=1)
-> Table scan on reservations (cost=9439 rows=99673) (actual time=0.342..51.8 rows=100000 loops=1)
|
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

-- Apply bad index
mysql> CREATE INDEX idx_reservations_status ON reservations(status);


-- Status only result
mysql> EXPLAIN ANALYZE SELECT * FROM reservations WHERE status = 'CONFIRMED' AND reserved_at >= DATE_SUB(NOW(), INTERVAL 3 DAY);
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Filter: (reservations.reserved_at >= <cache>((now() - interval 3 day))) (cost=2070 rows=16610) (actual time=1.5..187 rows=1427 loops=1)
-> Index lookup on reservations using idx_reservations_status (status='CONFIRMED') (cost=2070 rows=49836) (actual time=1.49..181 rows=80000 loops=1)
|
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

-- Switch index
mysql> DROP INDEX idx_reservations_status ON reservations;


-- Apply good index
mysql> CREATE INDEX idx_reservations_reserved_at ON reservations(reserved_at);


-- Reserved_at result
mysql> EXPLAIN ANALYZE SELECT * FROM reservations WHERE status = 'CONFIRMED' AND reserved_at >= DATE_SUB(NOW(), INTERVAL 3 DAY);
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Filter: (reservations.`status` = 'CONFIRMED') (cost=788 rows=175) (actual time=0.443..3.54 rows=1427 loops=1)
-> Index range scan on reservations using idx_reservations_reserved_at over ('2026-05-20 22:13:40' <= reserved_at), with index condition: (reservations.reserved_at >= <cache>((now() - interval 3 day))) (cost=788 rows=1750) (actual time=0.434..3.26 rows=1750 loops=1)
|
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
26 changes: 26 additions & 0 deletions docs/performance-logs/case3_orderby_index.txt
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Case 3. ORDER BY optimization

-- Before
mysql> EXPLAIN ANALYZE SELECT * FROM store_orders ORDER BY total_price DESC LIMIT 100;
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Limit: 100 row(s) (cost=10087 rows=100) (actual time=60..60 rows=100 loops=1)
-> Sort: store_orders.total_price DESC, limit input to 100 row(s) per chunk (cost=10087 rows=99828) (actual time=60..60 rows=100 loops=1)
-> Table scan on store_orders (cost=10087 rows=99828) (actual time=0.303..44.1 rows=100000 loops=1)
|
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

-- Apply
mysql> CREATE INDEX idx_store_orders_total_price ON store_orders(total_price);


-- After
mysql> EXPLAIN ANALYZE SELECT * FROM store_orders ORDER BY total_price DESC LIMIT 100;
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Limit: 100 row(s) (cost=0.114 rows=100) (actual time=1.16..1.51 rows=100 loops=1)
-> Index scan on store_orders using idx_store_orders_total_price (reverse) (cost=0.114 rows=100) (actual time=1.16..1.5 rows=100 loops=1)
|
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
50 changes: 50 additions & 0 deletions docs/performance-logs/case4_covering_index.txt
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Case 4. WHERE + ORDER BY + covering index

-- Reset
mysql> DROP INDEX idx_reservations_reserved_at ON reservations;


-- Before
mysql> EXPLAIN ANALYZE SELECT id, status, reserved_at, total_price FROM reservations WHERE member_id = 1 ORDER BY reserved_at DESC LIMIT 10;
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Limit: 10 row(s) (cost=10104 rows=10) (actual time=44..44 rows=10 loops=1)
-> Sort: reservations.reserved_at DESC, limit input to 10 row(s) per chunk (cost=10104 rows=99673) (actual time=44..44 rows=10 loops=1)
-> Filter: (reservations.member_id = 1) (cost=10104 rows=99673) (actual time=0.255..43.9 rows=150 loops=1)
-> Table scan on reservations (cost=10104 rows=99673) (actual time=0.254..39.4 rows=100000 loops=1)
|
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

-- Apply single index
mysql> CREATE INDEX idx_reservations_member_id ON reservations(member_id);


-- Single index result
mysql> EXPLAIN ANALYZE SELECT id, status, reserved_at, total_price FROM reservations WHERE member_id = 1 ORDER BY reserved_at DESC LIMIT 10;
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Limit: 10 row(s) (cost=52.5 rows=10) (actual time=0.314..0.315 rows=10 loops=1)
-> Sort: reservations.reserved_at DESC, limit input to 10 row(s) per chunk (cost=52.5 rows=150) (actual time=0.313..0.313 rows=10 loops=1)
-> Index lookup on reservations using idx_reservations_member_id (member_id=1) (cost=52.5 rows=150) (actual time=0.0815..0.272 rows=150 loops=1)
|
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

-- Switch to covering index
mysql> DROP INDEX idx_reservations_member_id ON reservations;


-- Apply covering index
mysql> CREATE INDEX idx_reservations_member_reserved_at_cover ON reservations(member_id, reserved_at DESC, status, total_price);


-- Covering result
mysql> EXPLAIN ANALYZE SELECT id, status, reserved_at, total_price FROM reservations WHERE member_id = 1 ORDER BY reserved_at DESC LIMIT 10;
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Limit: 10 row(s) (cost=17.9 rows=10) (actual time=0.0457..0.0502 rows=10 loops=1)
-> Covering index lookup on reservations using idx_reservations_member_reserved_at_cover (member_id=1) (cost=17.9 rows=150) (actual time=0.0447..0.0485 rows=10 loops=1)
|
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
14 changes: 14 additions & 0 deletions docs/performance-sql/case1_where_index.sql
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SELECT 'Before' AS stage;
EXPLAIN ANALYZE
SELECT *
FROM reservations
WHERE member_id = 1;

CREATE INDEX idx_reservations_member_id
ON reservations(member_id);

SELECT 'After' AS stage;
EXPLAIN ANALYZE
SELECT *
FROM reservations
WHERE member_id = 1;
30 changes: 30 additions & 0 deletions docs/performance-sql/case2_selective_index.sql
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DROP INDEX idx_reservations_member_id ON reservations;

SELECT 'Before' AS stage;
EXPLAIN ANALYZE
SELECT *
FROM reservations
WHERE status = 'CONFIRMED'
AND reserved_at >= DATE_SUB(NOW(), INTERVAL 3 DAY);

CREATE INDEX idx_reservations_status
ON reservations(status);

SELECT 'Status only result' AS stage;
EXPLAIN ANALYZE
SELECT *
FROM reservations
WHERE status = 'CONFIRMED'
AND reserved_at >= DATE_SUB(NOW(), INTERVAL 3 DAY);

DROP INDEX idx_reservations_status ON reservations;

CREATE INDEX idx_reservations_reserved_at
ON reservations(reserved_at);

SELECT 'Reserved_at result' AS stage;
EXPLAIN ANALYZE
SELECT *
FROM reservations
WHERE status = 'CONFIRMED'
AND reserved_at >= DATE_SUB(NOW(), INTERVAL 3 DAY);
16 changes: 16 additions & 0 deletions docs/performance-sql/case3_orderby_index.sql
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SELECT 'Before' AS stage;
EXPLAIN ANALYZE
SELECT *
FROM store_orders
ORDER BY total_price DESC
LIMIT 100;

CREATE INDEX idx_store_orders_total_price
ON store_orders(total_price);

SELECT 'After' AS stage;
EXPLAIN ANALYZE
SELECT *
FROM store_orders
ORDER BY total_price DESC
LIMIT 100;
33 changes: 33 additions & 0 deletions docs/performance-sql/case4_covering_index.sql
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DROP INDEX idx_reservations_reserved_at ON reservations;

SELECT 'Before' AS stage;
EXPLAIN ANALYZE
SELECT id, status, reserved_at, total_price
FROM reservations
WHERE member_id = 1
ORDER BY reserved_at DESC
LIMIT 10;

CREATE INDEX idx_reservations_member_id
ON reservations(member_id);

SELECT 'Single index result' AS stage;
EXPLAIN ANALYZE
SELECT id, status, reserved_at, total_price
FROM reservations
WHERE member_id = 1
ORDER BY reserved_at DESC
LIMIT 10;

DROP INDEX idx_reservations_member_id ON reservations;

CREATE INDEX idx_reservations_member_reserved_at_cover
ON reservations(member_id, reserved_at DESC, status, total_price);

SELECT 'Covering result' AS stage;
EXPLAIN ANALYZE
SELECT id, status, reserved_at, total_price
FROM reservations
WHERE member_id = 1
ORDER BY reserved_at DESC
LIMIT 10;
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