pgpool就是一個架在數據庫與應用系統之間的中間層，用于實現cluster或分布式數據庫，實現數據庫的大規模集成應用，類以于oracle的Tuxedo；不過這個是開源的，功能上也有一些限制，具體應用去它的官網上去看，下面主要分析它的實現原理

對于replication，它和MysqL一樣是通過傳遞sql實現的，對于分布式存儲，它是把sql經過parse,rewrite之后，生成經過優化后的sql分別在結點上執行，再把結果匯總。

對postgresql的通訊是通過libpq和socket實現的，對于自身多結點的通訊是通過socket實現的，對于一臺機器的多個進程間是通過pipe和unix domain socket通信的

pgpool也和postgresql一樣是多進程的，主要分為main進程，child進程,pcp進程，main進程主要是health check和消息中轉，child進程負責與postgresql通訊，pcp進程負責與其它的pgpool進程通訊和用戶名密碼的檢查，pcp之間的通訊全是用一個字母代表語義，這個通訊協議還需要看看是不是采用的是postgresql中的通訊協議，在pcp目錄下面，還保存了一些用戶管理pgpool的工具

pgpool的數據庫結點分為兩類，第一是node db就是普通的數據庫結點，第二是system db這個在分布式存儲中主要存儲分布的規則，在query cache中用來保存cache，這在一個pgpool的緩沖池中只有一個

在結構體中，第一個最重要的是

typedef struct {

char *listen_addresses; /* hostnames/IP addresses to listen on */

int port; /* port # to bind */

int pcp_port; /* PCP port # to bind */

char *socket_dir; /* pgpool socket directory */

char *pcp_socket_dir; /* PCP socket directory */

int pcp_timeout; /* PCP timeout for an idle client */

int num_init_children; /* # of children initially pre-forked */

int child_life_time; /* if idle for this seconds,child exits */

int connection_life_time; /* if idle for this seconds,connection closes */

int child_max_connections; /* if max_connections received,child exits */

int client_idle_limit; /* If client_idle_limit is n (n > 0),the client is forced to be

disconnected after n seconds idle */

int authentication_timeout; /* maximum time in seconds to complete client authentication */

int max_pool; /* max # of connection pool per child */

char *logdir; /* logging directory */

char *pid_file_name; /* pid file name */

char *backend_socket_dir; /* Unix domain socket directory for the Postgresql server */

int replication_mode; /* replication mode */

int log_connections; /* 0:false,1:true - logs incoming connections */

int log_hostname; /* 0:false,1:true - resolve hostname */

int enable_pool_hba; /* 0:false,1:true - enables pool_hba.conf file authentication */

int load_balance_mode; /* load balance mode */

int replication_stop_on_mismatch; /* if there's a data mismatch between master and secondary

* start degenration to stop replication mode

*/

int replicate_select; /* if non 0,replicate SELECT statement when load balancing is disabled. */

char **reset_query_list; /* comma separated list of quries to be issued at the end of session */

int print_timestamp; /* if non 0,print time stamp to each log line */

int master_slave_mode; /* if non 0,operate in master/slave mode */

int connection_cache; /* if non 0,cache connection pool */

int health_check_timeout; /* health check timeout */

int health_check_period; /* health check period */

char *health_check_user; /* Postgresql user name for health check */

char *failover_command; /* execute command when failover happens */

char *failback_command; /* execute command when failback happens */

/*

* If true,trigger fail over when writing to the backend

* communication socket fails. This is the same behavior of

* pgpool-II 2.2.x or earlier. If set to false,pgpool will report

* an error and disconnect the session.

*/

int fail_over_on_backend_error;

char *recovery_user; /* Postgresql user name for online recovery */

char *recovery_password; /* Postgresql user password for online recovery */

char *recovery_1st_stage_command; /* Online recovery command in 1st stage */

char *recovery_2nd_stage_command; /* Online recovery command in 2nd stage */

int recovery_timeout; /* maximum time in seconds to wait for remote start-up */

int client_idle_limit_in_recovery; /* If > 0,the client is forced to be

* disconnected after n seconds idle

* This parameter is only valid while in recovery 2nd statge */

int insert_lock; /* if non 0,automatically lock table with INSERT to keep SERIAL

data consistency */

int ignore_leading_white_space; /* ignore leading white spaces of each query */

int log_statement; /* 0:false,1: true - logs all sql statements */

int log_per_node_statement; /* 0:false,1: true - logs per node detailed sql statements */

int parallel_mode; /* if non 0,run in parallel query mode */

int enable_query_cache; /* if non 0,use query cache. 0 by default */

char *pgpool2_hostname; /* pgpool2 hostname */

char *system_db_hostname; /* system DB hostname */

int system_db_port; /* system DB port number */

char *system_db_dbname; /* system DB name */

char *system_db_schema; /* system DB schema name */

char *system_db_user; /* user name to access system DB */

char *system_db_password; /* password to access system DB */

char *lobj_lock_table; /* table name to lock for rewriting lo_creat */

BackendDesc *backend_desc; /* Postgresql Server description. Placed on shared memory */

LOAD_BALANCE_STATUS load_balance_status[MAX_NUM_BACKENDS]; /* to remember which DB node is selected for load balancing */

/* followings do not exist in the configuration file */

int current_slot; /* current backend slot # */

int replication_enabled; /* replication mode enabled */

int master_slave_enabled; /* master/slave mode enabled */

int num_reset_queries; /* number of queries in reset_query_list */

/* ssl configuration */

int ssl; /* if non 0,activate ssl support (frontend+backend) */

char *ssl_cert; /* path to ssl certificate (frontend only) */

char *ssl_key; /* path to ssl key (frontend only) */

char *ssl_ca_cert; /* path to root (CA) certificate */

char *ssl_ca_cert_dir; /* path to directory containing CA certificates */

} POOL_CONFIG;

POOL_CONFIG里面保存了pgpool的配置信息，是從配置文件中讀入的，這里面最重要的是BackendDesc *backend_desc，它里面保存了pgpool和數據庫的連接信息，是放在共享內存中，供所有pgpool的child進程共享的。其余的字段看注釋就可以了

每一個BackendInfo對應一個數據庫連接，其實就是postgresql的一個進程

/*

* Postgresql backend descriptor. Placed on shared memory area.

*/

typedef struct {

char backend_hostname[MAX_DB_HOST_NAMELEN]; /* backend host name */

int backend_port; /* backend port numbers */

BACKEND_STATUS backend_status; /* backend status */

double backend_weight; /* normalized backend load balance ratio */

double unnormalized_weight; /* descripted parameter */

char backend_data_directory[MAX_PATH_LENGTH];

} BackendInfo;

typedef struct {int num_backends; /* number of used Postgresql backends */BackendInfo backend_info[MAX_NUM_BACKENDS];} BackendDesc;

相關文章

總結

以上是編程之家為你收集整理的pgpool分析二全部內容，希望文章能夠幫你解決pgpool分析二所遇到的程序開發問題。

如果覺得編程之家網站內容還不錯，歡迎將編程之家網站推薦給程序員好友。

本圖文內容來源于網友網絡收集整理提供，作為學習參考使用，版權屬于原作者。

如您喜歡交流學習經驗，點擊鏈接加入交流1群：1065694478(已滿)交流2群：163560250

總結

以上是生活随笔為你收集整理的pgpool mysql_pgpool分析二的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。