SQLite usage

SQLite

● Good○ File based○ Development○ Small

● Bad○ No ACL○ Performance○ Alow only one write at a time

SQLite Flow

● Create DB/table/index● Prepare SQL● SQL bind● SQL Query

Create DB/table/index#define CMD_CREATE_DP_TABLE "CREATE TABLE IF NOT EXISTS `data_planner` (" \

"`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL," \

"`tx_bytes` bigint(20) NOT NULL," \

"`rx_bytes` bigint(20) NOT NULL," \

"`timestamp` datetime);"

#define CMD_CREATE_DP_INDEX "CREATE INDEX IF NOT EXISTS `timestamp_idx` ON \

`data_planner` (`timestamp` DESC);"

Create DB/table/index sqlite3 *db = NULL;

char *err_msg = NULL;

int ret = -1;

if (sqlite3_open(DATA_PLANNER_DB_PATH, &db) != SQLITE_OK) {

syslog(LOG_ERR, "Open sqlite fail: %s", DATA_PLANNER_DB_PATH);

goto out;

}

if (sqlite3_exec(db, CMD_CREATE_DP_TABLE, NULL, NULL, &err_msg) != SQLITE_OK) {

syslog(LOG_ERR, "Create data_planner table fail: %s", err_msg);

goto out;

}

if (err_msg) sqlite3_free(err_msg);

Create DB/table/index if (sqlite3_exec(db, CMD_CREATE_DP_INDEX, NULL, NULL, &err_msg) != SQLITE_OK) {

syslog(LOG_ERR, "Create data_planner index fail: %s", err_msg);

goto out;

}

ret = 0;

out:

if (err_msg) sqlite3_free(err_msg);

if (db) sqlite3_close(db);

return ret;

Create DB/table/index

● Check if using index● “EXPLAIN <your query>”

○ ex: EXPLAIN SELECT * FROM a WERHE name = “1”;

○ Will show IdxRowid/IdxGE if apply index

Create DB/table/indexsqlite> explain select * from users where name='foo';

0|Trace|0|0|0||00|1|String8|0|1|0|foo|00|2|Goto|0|18|0||00|3|OpenRead|0|2|0|2|00|4|OpenRead|1|3|0|keyinfo(1,BINARY)|00|5|IsNull|1|15|0||00|6|Affinity|1|1|0|bb|00|7|SeekGe|1|15|1|1|00|8|IdxGE|1|15|1|1|01|9|IdxRowid|1|2|0||00|...blahblah21|Goto|0|3|0||00|

Create DB/table/index

● When to create?○ System startup○ Program startup○ In every query

Prepare SQL sqlite3 *db = NULL; sqlite3_stmt *stmt = NULL; int ret = DP_ERROR;

if (sqlite3_open(DATA_PLANNER_DB_PATH, &db) != SQLITE_OK) { syslog(LOG_ERR, "Open sqlite fail: %s", DATA_PLANNER_DB_PATH);goto out;

} char *sql = "SELECT sum(tx_bytes) as total_tx_bytes,sum(rx_bytes) as total_rx_bytes \

FROM data_planner WHERE datetime(timestamp, 'localtime') >= ? AND datetime(timestamp, 'localtime') < ?;";

if (sqlite3_prepare_v2(db, sql, strlen(sql), &stmt, NULL) != SQLITE_OK) {syslog(LOG_ERR, "SQL prepare fail: %s", sql);goto out;

}

SQL Bindsqlite3_bind_text(stmt, 1, begin_date, -1, NULL);sqlite3_bind_text(stmt, 2, end_date, -1, NULL);

// Also, there is no uint64, only int64

SQL Queryif (sqlite3_step(stmt) == SQLITE_ROW) {

*total_tx_bytes = sqlite3_column_int64(stmt, 0);*total_rx_bytes = sqlite3_column_int64(stmt, 1);

} else {syslog(LOG_ERR, "SQL fail: Error when get previous total data: %s", sqlite3_errmsg(db));goto out;

}

ret = 0;

out:if (stmt) sqlite3_finalize(stmt);if (db) sqlite3_close(db);return ret;

SQL Query

● sqlite3_exec○ sqlite3_prepare_v2 + sqlite3_step + sqlite3_finalize○ Good for insertion/create table/transaction○ Bad for query

SQL Querysqlite3_exec(

sqlite3*,const char *sql,int (*callback)(void*, int column_num, char**, char**),void *,char **errmsg

}// void * is for user data

Timezone issue

● Use UTC● In C

○ Use gmtime_r instead of localtime_r● In SQLite3

○ Insert using datetime(?, 'unixepoch')■ ? is time_t

○ Query using datetime(timestamp, 'localtime')

SQL Debugvoid* sqlite3_trace( sqlite3* db, trace_callback, void* udp);

// Register sql callback and call it every time before executing

void trace_callback( void* udp, const char* sql );

// udp means user data pointer

SQLite Busy Handle

● SQlite may be locked sometimes, solution:○ sqlite3_busy_handle

■ More flexible, can add sleep() and retry times○ sqlite3_busy_timeout○ http://www.bubuko.com/infodetail-240892.html○ http://www.360doc.

com/content/10/1214/12/87000_77984300.shtml

Relational Database

● MariaDB/MySQL/Percona○ Multiple engines

■ MyISAM● Table lock

■ InnoDB● Row lock● Transaction

● PostgreSQL● SQLite

Relational Database

● Replication○ For read○ Master/Slave

● Sharding○ For read/write○ Do not rely on auto sharding

Reference● http://stackoverflow.com/questions/1454188/how-can-i-analyse-a-sqlite-query-execution● https://www.sqlite.org/docs.html● http://www.cnblogs.com/likebeta/archive/2012/06/17/2552757.html