A detailed introduction to PostgreSQL version identification
Today's editor to share with you is a detailed introduction of PostgreSQL version identification, I believe many people do not know much, in order to let you know more about PostgreSQL version identification, so give you a summary of the following content, let's look down. I'm sure you'll get something.
Insert\ delete\ update locates through the ctid and looks at the changes to the record xmin\ xmax.
Xid: transactional ID of the database
Xmin: the xid information of the row header. Xmin represents the transaction ID that inserted the record.
Xmax: indicates the transaction ID that deletes or lock the record
Xid_snapshot: the transaction that is ending in the current cluster
Clog: transaction commit status log
The definition of record format: htup_details.h:POSTGRES heap tuple header definitions.
1) check which functions are related to xid. What is needed here is the txid_current function.
2) you can see the current transaction ID
Postgres=# select * from txid_current (); txid_current- 1676 (1 row) 3) after insert, the transaction ID has been + 1postgres=# insert into tt values (1); INSERT 0 1postgres=# select ctid,xmin,xmax,cmin,cmax,id from tt Ctid | xmin | xmax | cmin | cmax | id-+---- (0jue 1) | 1677 | 0 | 0 | 1 (1 row)
4) after starting a transaction, update
Postgres=# begin;BEGIN postgres=# update tt set id=3;UPDATE 1postgres=# select ctid,xmin,xmax,cmin,cmax,id from tt; ctid | xmin | xmax | cmin | cmax | id-+---- (0jue 2) | 1678 | 0 | 0 | 3 (1 row)
5) View in another session
Postgres=# select ctid,xmin,xmax,cmin,cmax,id from tt; ctid | xmin | xmax | cmin | cmax | id-+---- (0jue 1) | 1677 | 1678 | 0 | 0 | 1 (1 row)
Look at currently unfinished transactions, or unopened transactions
Postgres=# select * from txid_current_snapshot (); txid_current_snapshot--- 1684 postgres=# select 1684: (1 row) postgres=# select * from txid_current (); txid_current- 1684 (1 row)
Record whether the transaction is committed. In this file, bit:
-rw-. 1 pg pg 8192 Jun 10 04:19 0000 [pg@localhost pg_clog] $pwd/home/pg/data/pg_clog
The above is a detailed introduction to the identification of the PostgreSQL version. Have you gained anything after reading it? If you want to know more about it, welcome to the industry information!
