How to add a system table field to PostgreSQL

1. Bki Introduction: http://www.postgresql.org/docs/9.4/static/bki.html

Can not understand, nor affect us to continue, because there are many examples of ready-made reference;

2. Add a field datdummy for Pg_database to open/src/include/catalog/pg_database.h:

CATALOG (pg_database,1262)  bki_shared_relation bki_rowtype_oid (1248)  bki_schema_macro{ namedatadatname;/* database name */oiddatdba;/* owner of database */ int32encoding;/* character encoding */namedatadatcollate;/* lc_collate setting * /namedatadatctype;/* lc_ctype setting */booldatistemplate;/* allowed as create  database template? */booldatallowconn;/* new connections allowed? */ int32datconnlimit;/* max connections allowed  ( -1=no limit)  */Oiddatlastsysoid;/*  highest OID to consider a system OID */TransactionId  Datfrozenxid; /* all xids < this are frozen in this db  */transactionid datminmxid;/* all multixacts in the db are >=  this */oiddattablespace;/* default table space for this db */#ifdef  catalog_varlen/* variable-length  fields start here */aclitemdatacl[1];/* access permissions */#endif}  formdata_pg_database;/* ---------------- *Form_pg_database corresponds to a  Pointer to a tuple with *the format of pg_database relation.  * ---------------- */typedef FormData_pg_database *Form_pg_database;/* -------- -------- *compiler constants for pg_database * ---------------- */#define  natts_pg_database13#define anum_pg_database_datname1#define anum_pg_database_datdba2#define  anum_pg_database_encoding3#define anum_pg_database_datcollate4#define anum_pg_database_ datctype5#define anum_pg_database_datistemplate6#define anum_pg_database_datallowconn7#define  Anum_pg_database_datconnlimit8#defiNe anum_pg_database_datlastsysoid9#define anum_pg_database_datfrozenxid10#define anum_pg_ Database_datminmxid11#define anum_pg_database_dattablespace12#define anum_pg_database_datacl13

They will eventually be used by the script genbki.pl to generate the Postgresql.bki file, used in the INITDB initialization of data cluster, interested in learning, PG compilation system is a full display of the powerful perl language system;

3. Add a new definition under Dattablespace:

int8datdummy;/* Dummy Column */

The definition of the following field ordinal is also important and must be modified in order, as well as the corresponding modification of the attribute number:

#define NATTS_PG_DATABASE14 #define Anum_pg_database_dattablespace12#define Anum_pg_database_datdummy13#define Anum_pg_database_datacl14

The pre-defined database must also be modified, adding 100 fields to the _null_ front datdummy data:

DATA (Insert OID = 1 (template1 pguid ENCODING "lc_collate" "lc_ctype" T t-1 0 0 1 1663 (_null_)));

4, compile run, what will happen, compile normal, then initdb, unexpectedly also magically passed, is this good?

Tip:linux under a directory to change the code, you may encounter inexplicable program problems, try make clean

5, then create a database to try: Creation database Quanzl; Success, is not the feeling seems to have shortcomings what?

Datdummy assignment, can not UPDATE pg_database SET datdummy = xxx bar?

Subscribe to a database like template1, we can define a BKI script in the catalog, such as the above example, giving it an initial value. The program must also be changed in order to become an operational attribute;

6, referring to the syntax modification, creating a CREATE DATABASE xxx DUMMY nnn syntax, modifying the structure createdbstmt add a new attribute, the parsing phase will read this value in the creation of databases when it is written to the property;

NEW_RECORD[ANUM_PG_DATABASE_DATDUMMY-1] = 1234;

This part of the code in the SRC/BACKEND/COMMANDS/DBCOMMANDS.C, self-reading, write the program is so simple. :)

How to add a system table field to PostgreSQL