Pearl DB Service

1. bgwriter 2. check pointer 3. stats collector 4. sys logger 5. auto vacuum launcher 6. wal writer 7. archiver Bgwriter: When a PostgreSQL server process reads data from disk, it first moves the page that contains the data into the shared buffer pool. The shared buffer pool is so named because it's a region of memory that's shared by all server processes that access a given cluster. Another way to look at it is that the shared buffer pool is shared by all processes spawned by a single postmaster. When the shared buffer pool fills, PostgreSQL starts pushing old pages out of the pool to make room for new ones. PostgreSQL uses the LRU (least-recently-used) mechanism to select the page it evicts from the pool. If PostgreSQL chooses a page that has not been modified since it was placed in the pool, that page is simply discarded. On the other hand, if PostgreSQL chooses a page that has been modified, it must write the page to disk. The BGWRITER improves overall perfo

  Parser: The parser stage consists of two parts: The parser defined in gram.y and scan.l is built using the UNIX tools bison and flex. The parser has to check the query string (which arrives as plain text) for valid syntax. If the syntax is correct a parse tree is built up and handed back; otherwise an error is returned. The parser is defined in the file gram.y and consists of a set of grammar rules and actions that are executed whenever a rule is fired. The code of the actions (which is actually C code) is used to build up the parse tree. The lexer is defined in the file scan.l and is responsible for recognizing identifiers, the SQL key words etc. For every key word or identifier that is found, a token is generated and handed to the parser. The file scan.l is transformed to the C source file scan.c using the program flex and gram.y is transformed to gram.c using bison. After these transformations have taken place a normal C compiler can be used to create the pa