(数据库原理及应用笔记)数据库管理系统

• The component of DBMS core

-> UFI （即席访问）
-> APIs （类库、嵌入式…）
-> Access management （访问原语）

• The process structure of DBMS

-> Single process structure

-> Multi processes structure

-> Multi threads structure

-> Communication protocols between processes/threads

1. Access types
   （ Query all or most records of a file(>15%)
   （ Query some special record
   （ Query some records(<15%)
   （ Scope query
   （ Update
2. File organization
   （ Heap file
   （ Direct file
   （ Indexed file：index + heap file/cluster ->B+Tree
   （ Dynamic hashing
   （ Grid structure file
   （ Raw disk
3. Index technique
   （ B+ Tree
   （ Clustering index(簇集索引)
   （ Inverted file
   （ Dynamic hashing
   （ Grid structure file and partitioned hash function
   （ Bitmap index(used in data warehouse)
   （ Others
4. Access primitives
   -> Algebra Optimization（Rewrite
   -> Operation Optimization（存储结构、索引

S(SNUM, SNAME, CITY)
SP(SNUM, PNUM, QUAN)
P(PNUM, PNAME, WEIGHT, SIZE)
SELECT SNAME
FROM S, SP, P
WHERE S.SNUM=SP.SNUM AND
SP.PNUM=P.PNUM AND
S.CITY=‘Nanjing’ AND
P.PNAME=‘Bolt’ AND
SP.QUAN>1000;

• The operation optimization of the tree
  -> Nest Loop,R as O,S as I
  -> Nest Loop,R as I,S as O
  -> Nest Loop,use possible index on R or S
  -> Merge Scan
  -> Hash join
• Algebra optimization
  -> Exchange rule of ⋈/×: E1 × E2 ≡ E2 ×E1
  -> Combination rule of ⋈/×: E1×(E2×E3)≡(E1×E2)×E3
  -> Cluster rule of ∏: ∏A1…An(∏B1…Bm(E))≡∏A1…An(E),
  legal when A1…An is the sub set of {B1…Bm}
  -> Cluster rule of δ: δF1(δF2(E))≡δF1∧F2(E)
  -> Exchange rule of ∏ and δ: δF(∏A1…An(E))≡∏A1…An (δF(E)) if F includes attributes B1…Bm which don’t belong to A1…An, then ∏A1…An (δF(E)) ≡ ∏A1…An δF(∏A1…An， B1…Bm(E))
  -> If the attributes in F are all the attributes in E1, thenδF(E1×E2) ≡ δF(E1)×E2；
  if F in the form of F1∧F2, and there are only E1’s attributes in F1, and there are only E2‟s attributes in F2, then δF(E1×E2) ≡δF1(E1)×δF2(E2)；
  if F in the form of F1∧F2, and there are only E1‟s
  attributes in F1, while F2 includes the attributes both in E1 and E2, then δF(E1×E2) ≡δF2(δF1(E1)×E2)；
  -> δF(E1 ⋃ E2) ≡ δF(E1) ⋃ δF(E2)
  -> δF(E1 - E2) ≡ δF(E1) - δF(E2)
  -> Suppose A1…An is a set of attributes, in which B1…Bm are E1‟s attributes, and C1…Ck are E2‟s attributes, then∏A1…An(E1×E2)≡∏B1…Bm(E1)×∏C1…Ck(E2)
  -> ∏A1…An(E1 ⋃ E2)≡∏A1…An(E1) ⋃ ∏A1…An(E2)
• Basic principles
  -> Push down the unary operations as low as possible
  -> Look for and combine the commo n sub-expression
• The operation optimization
  -> Optimization of select operation
  -> Optimization of project operation
  -> Optimization of set operation
  -> Optimization of join operation
  -> Optimization of combined operations
• Recovery
  -> Reducing the likelihood of failures
  -> Recover from failures
  -> Restore DB to aconsistent state after some failures
  （Redundancy is necessary
  （Should inspect all possible failures
  -> Periodical dumping
  
  -> Backup + Log
  
• Transaction
  -> Atomic action
  -> Consistency preservation(保持一致性)
  -> Isolation
  -> Durability
• Some structures to support recovery
  -> Commit list
  -> Active list
  -> Log
  
• Commit rule and Log ahead rule
  -> Commit rule: A.I must be written to nonvolatile strorage(非挥发存储器) before commit of the transaction
  -> Log ahead rule: If A.I is written to DB before commit then B.I must first written to log
  -> Recovery strategies
• Three kinds of update strategy
  -> A.I-DB before commit
  -> A.I-D.B after commit
  -> A.I-D.B concurrently with commit
  -> 异地更新
• Concurrency control
  -> Serializable
• Locking Protocol
• X locks
  

-> Conclusions
-> Well-formed + 2PL: serializable
-> Well-formed + 2PL + unlock update at EOT: serializable and recoverable.(without domino phenomena)
-> Well-formed + 2PL + holding all locks to EOT: strict two phase locking transaction

• (S,X) locks
  -> S lock — if read access is intended.
  -> X lock — if update access is intended.
  - (S,U,X) locks
  -> U lock — update lock.For an update access the transaction first acquires a U-lock and then promote it to X-lock.
  -> Purpose — shorten the time of exclusion,so as to boost concurrency degree, and reduce deadlock.
  
• Deadlock & Livelock
  -> Deadlock — wait in cycle,no transaction can obtain all of resources needed to complete
  -> Prevention(do not let it occur)
  -> Solving(permit it occurs,but can solve it)
  

-> Livelock — although other transaction release their resource in limited time,some transaction can not get the resources needed for a very long time.
-> Adjust schedule strategy,such as FIFO

• Deadlock Detection
  -> Timeout
  -> Detect deadlock by wait-for graph G=<V,E>
  -> When to detect? —
  whenever one transaction waits.
  -> What to do when detected? —
  ①Pick a victim；
  ②Abort the victim and release its locks and resources；
  ③Grant a waiter；
  ④Restart the victim(automatically or manually)
  -> Deadlock avoidance —
  ①Requestin all locks at initial time of transaction
  ②Requesting locks in a specified order of resource
  ③Abort once conflicted
  ④Transaction Retry
  -> Every transaction is uniquely time stamped.If Ta requires a lock on a data object that is already locked by Tb,one of the following methods is uesd
  ①Wait-die
  ②Wound-wait
  In above,both have only one direction wait,either older->younger or younger->older.It is impossible to occur wait in cycle,so the dead lock is avoided.