WiredTiger: ex_extractor.c

| Version 3.1.0

Fork me on GitHub Join my user group
ex_extractor.c

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

/*-
* Public Domain 2014-2018 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);
}