PostgreSQL/開発/フック/commands

PostgreSQL/開発/フック

フック †

 参考  commands/explain.c - on doxygen.postgresql.org

サンプル †

 実験 

myext.c

#include "postgres.h"
#include "fmgr.h"
#include "commands/explain.h"
#include "lib/stringinfo.h"
#include "tcop/tcopprot.h"

PG_MODULE_MAGIC;

extern void _PG_init(void);


extern ExplainOneQuery_hook_type ExplainOneQuery_hook;
extern explain_get_index_name_hook_type explain_get_index_name_hook;


static void my_ExplainOneQuery_hook(Query *query,
                                    IntoClause *into,
                                    ExplainState *es,
                                    const char *queryString,
                                    ParamListInfo params);

static const char* my_explain_get_index_name(Oid indexId);

// フックの初期化
void _PG_init(void)
{
    ExplainOneQuery_hook = my_ExplainOneQuery_hook;
    explain_get_index_name_hook = my_explain_get_index_name;
}

// ExplainOneQuery_hook
static void my_ExplainOneQuery_hook(Query *query,
                                    IntoClause *into,
                                    ExplainState *es,
                                    const char *queryString,
                                    ParamListInfo params)
{
    PlannedStmt *plan;
    instr_time	planstart, planduration;

    elog(INFO, "*** my_ExplainOneQuery_hook ***");
    appendStringInfo(es->str, "%s\n\n", "[Explain by my_ExplainOneQuery_hook]");


    INSTR_TIME_SET_CURRENT(planstart);

    plan = pg_plan_query(query, into ? 0 : CURSOR_OPT_PARALLEL_OK, params);

    INSTR_TIME_SET_CURRENT(planduration);
    INSTR_TIME_SUBTRACT(planduration, planstart);

    ExplainOnePlan(plan, into, es, queryString, params, &planduration);
}

// explain_get_index_name_hook
static const char * my_explain_get_index_name(Oid indexId)
{
    // 適当に固定値を返してみる
    return "MyIndex";
}

postgresql.conf

shared_preload_libraries = 'my ext'

実行例

postgres=# EXPLAIN SELECT id, name FROM foo WHERE id = 5 ORDER BY id DESC;
INFO:  *** my_ExplainOneQuery_hook ***
                             QUERY PLAN                             
--------------------------------------------------------------------
 [EXPLAIN BY my_ExplainOneQuery_hook]

 INDEX Scan USING MyIndex ON foo  (cost=0.28..8.29 ROWS=1 width=10)
   INDEX Cond: (id = 5)
(4 ROWS)

参考リンク †

• commands/explain.c - on doxygen.postgresql.org