Detailed explanation of PostgreSQL version identification
Insert\delete\updateLocate via ctid, and view the changes in the record xmin\xmax.
Xid: Database transaction ID;
Xmin: Row header xidInformation, xmin represents the transaction that inserted the recordID
Xmax : Indicates deletion or lockThe transaction of this recordID
xid_snapshot: Ended in the current cluster Transaction
Clog: Transaction submission status log
Definition of record format: htup_details.h:POSTGRES heap tuple header definitions.
1) View all xid related functions. What is needed here is txid_currentFunction
##2）
can be seen Current transaction ID
postgres=# select * from txid_current();
txid_current
--------------
1676
(1 row)
3）进行一次insert后，看事务ID已经+1
postgres=# insert into tt values(1);
INSERT 0 1
postgres=# select ctid,xmin,xmax,cmin,cmax,id from tt;
ctid | xmin | xmax | cmin | cmax | id
-------+------+------+------+------+----
(0,1) | 1677 | 0 | 0 | 0 | 1
(1 row)After opening a transaction, proceed update
postgres=# begin; BEGIN postgres=# update tt set id=3; UPDATE 1 postgres=# select ctid,xmin,xmax,cmin,cmax,id from tt; ctid | xmin | xmax | cmin | cmax | id -------+------+------+------+------+---- (0,2) | 1678 | 0 | 0 | 0 | 3 (1 row)
postgres=# select ctid,xmin,xmax,cmin,cmax,id from tt; ctid | xmin | xmax | cmin | cmax | id -------+------+------+------+------+---- (0,1) | 1677 | 1678 | 0 | 0 | 1 (1 row)
## in another session to see the current unfinished transactions or unopened transactions Transaction
##
postgres=# select *from txid_current_snapshot();
txid_current_snapshot
-----------------------
1684:1684:
(1 row)
postgres=# select * from txid_current();
txid_current
--------------
1684
(1 row)Record whether the transaction is submitted, in In this file,
bit:
-rw-------. 1 pg pg 8192 Jun 10 04:19 0000 [pg@localhost pg_clog]$ pwd /home/pg/data/pg_clog
Explain what B/S and C/S are
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