ex_extractor.c

Shows how to extend WiredTiger with a more complex custom extractor.

/*-
 * Public Domain 2014-present MongoDB, Inc.
 * Public Domain 2008-2014 WiredTiger, Inc.
 *
 * This is free and unencumbered software released into the public domain.
 *
 * Anyone is free to copy, modify, publish, use, compile, sell, or
 * distribute this software, either in source code form or as a compiled
 * binary, for any purpose, commercial or non-commercial, and by any
 * means.
 *
 * In jurisdictions that recognize copyright laws, the author or authors
 * of this software dedicate any and all copyright interest in the
 * software to the public domain. We make this dedication for the benefit
 * of the public at large and to the detriment of our heirs and
 * successors. We intend this dedication to be an overt act of
 * relinquishment in perpetuity of all present and future rights to this
 * software under copyright law.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * ex_extractor.c
 *      Example of how to use a WiredTiger custom index extractor extension.
 */
#include <test_util.h>
 
static const char *home;
 
struct president_data {
    int id;
    const char *last_name;
    const char *first_name;
    uint16_t term_start;
    uint16_t term_end;
};
 
static const struct president_data example_data[] = {{0, "Obama", "Barack", 2009, 2014},
  {1, "Bush", "George W", 2001, 2009}, {2, "Clinton", "Bill", 1993, 2001},
  {3, "Bush", "George H", 1989, 1993}, {4, "Reagan", "Ronald", 1981, 1989}, {0, NULL, NULL, 0, 0}};
/*
 * Number of years this data spans
 */
#define YEAR_BASE 1981
#define YEAR_SPAN (2014 - 1981)
 
/*
 * A custom index extractor function that adds an index entry for each year of the given president's
 * term.
 */
static int
my_extract(WT_EXTRACTOR *extractor, WT_SESSION *session, const WT_ITEM *key, const WT_ITEM *value,
  WT_CURSOR *result_cursor)
{
    uint16_t term_end, term_start, year;
    char *last_name, *first_name;
 
    /* Unused parameters */
    (void)extractor;
    (void)key;
 
    /* Unpack the value. */
    error_check(wiredtiger_struct_unpack(
      session, value->data, value->size, "SSHH", &last_name, &first_name, &term_start, &term_end));
 
    /*
     * We have overlapping years, so multiple records may share the same index key.
     */
    for (year = term_start; year <= term_end; ++year) {
        /*
         * Note that the extract callback is called for all operations that update the table, not
         * just inserts. The user sets the key and uses the cursor->insert() method to return the
         * index key(s). WiredTiger will perform the required operation (such as a remove()).
         */
        fprintf(
          stderr, "EXTRACTOR: index op for year %" PRIu16 ": %s %s\n", year, first_name, last_name);
        result_cursor->set_key(result_cursor, year);
        error_check(result_cursor->insert(result_cursor));
    }
    return (0);
}
 
/*
 * The terminate method is called to release any allocated resources when the table is closed. In
 * this example, no cleanup is required.
 */
static int
my_extract_terminate(WT_EXTRACTOR *extractor, WT_SESSION *session)
{
    (void)extractor;
    (void)session;
 
    return (0);
}
 
static void
add_extractor(WT_CONNECTION *conn)
{
    static WT_EXTRACTOR my_extractor = {my_extract, NULL, my_extract_terminate};
    error_check(conn->add_extractor(conn, "my_extractor", &my_extractor, NULL));
}
 
/*
 * Read the index by year and print out who was in office that year.
 */
static void
read_index(WT_SESSION *session)
{
    WT_CURSOR *cursor;
    int i, ret;
    char *first_name, *last_name;
    uint16_t rec_year, term_end, term_start, year;
 
    year = 0;
    srand((unsigned int)getpid());
    error_check(session->open_cursor(session, "index:presidents:term", NULL, NULL, &cursor));
 
    /*
     * Pick 10 random years and read the data.
     */
    for (i = 0; i < 10; i++) {
        year = (uint16_t)((rand() % YEAR_SPAN) + YEAR_BASE);
        printf("Year %" PRIu16 ":\n", year);
        cursor->set_key(cursor, year);
        error_check(cursor->search(cursor));
        error_check(cursor->get_key(cursor, &rec_year));
        error_check(cursor->get_value(cursor, &last_name, &first_name, &term_start, &term_end));
 
        /* Report all presidents that served during the chosen year */
        ret = 0;
        while (term_start <= year && year <= term_end && year == rec_year) {
            printf("\t%s %s\n", first_name, last_name);
            if ((ret = cursor->next(cursor)) != 0)
                break;
            error_check(cursor->get_key(cursor, &rec_year));
            error_check(cursor->get_value(cursor, &last_name, &first_name, &term_start, &term_end));
        }
        scan_end_check(ret == 0 || ret == WT_NOTFOUND);
    }
 
    error_check(cursor->close(cursor));
}
 
/*
 * Remove some items from the primary table.
 */
static void
remove_items(WT_SESSION *session)
{
    WT_CURSOR *cursor;
    struct president_data p;
    int i;
 
    /*
     * Removing items from the primary table will call the extractor for the index and allow our
     * custom extractor code to handle each custom key.
     */
    error_check(session->open_cursor(session, "table:presidents", NULL, NULL, &cursor));
    /*
     * Just remove the first few items.
     */
    for (i = 0; example_data[i].last_name != NULL && i < 2; i++) {
        p = example_data[i];
        cursor->set_key(cursor, p.id);
        error_check(cursor->remove(cursor));
    }
}
 
/*
 * Set up the table and index of the data.
 */
static void
setup_table(WT_SESSION *session)
{
    WT_CURSOR *cursor;
    struct president_data p;
    int i;
 
    /* Create the primary table. It has a key of the unique ID. */
    error_check(session->create(session, "table:presidents",
      "key_format=I,value_format=SSHH,columns=(ID,last_name,first_name,term_begin,term_end)"));
 
    /*
     * Create the index that is generated with an extractor. The index will generate an entry in the
     * index for each year a president was in office.
     */
    error_check(session->create(
      session, "index:presidents:term", "key_format=H,columns=(term),extractor=my_extractor"));
 
    error_check(session->open_cursor(session, "table:presidents", NULL, NULL, &cursor));
    for (i = 0; example_data[i].last_name != NULL; i++) {
        p = example_data[i];
        cursor->set_key(cursor, p.id);
        cursor->set_value(cursor, p.last_name, p.first_name, p.term_start, p.term_end);
        fprintf(stderr, "SETUP: table insert %" PRIu16 "-%" PRIu16 ": %s %s\n", p.term_start,
          p.term_end, p.first_name, p.last_name);
        error_check(cursor->insert(cursor));
    }
}
 
int
main(int argc, char *argv[])
{
    WT_CONNECTION *conn;
    WT_SESSION *session;
 
    home = example_setup(argc, argv);
 
    error_check(wiredtiger_open(home, NULL, "create,cache_size=500M", &conn));
    add_extractor(conn);
    error_check(conn->open_session(conn, NULL, NULL, &session));
 
    setup_table(session);
    read_index(session);
    remove_items(session);
 
    error_check(conn->close(conn, NULL));
 
    return (EXIT_SUCCESS);
}