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//! An SQL-based storage manager
//!
//! This storage manager provides the means to save data to an SQL-based
//! backend.
//!
//! For now it's mysql only, dialectization will be added at a later time.
//! Serialization should be taken care of by the low-level SQL drivers.
//!
//! @note
//! An administrator is supposed to create the database and give
//! the user enough privileges to write to it. It will be care
//! of this driver to create the database tables itself.
//!
//! @thanks
//! Thanks to Francesco Chemolli <kinkie@@roxen.com> for the contribution.
#pike __REAL_VERSION__
inherit Cache.Storage.Base;
#define MAX_KEY_SIZE "255"
#define CREATION_QUERY "create table cache ( \
cachekey varchar(" MAX_KEY_SIZE ") not null primary key, \
atime timestamp, \
ctime timestamp, \
etime timestamp, \
cost float unsigned DEFAULT 1.0 NOT NULL, \
data longblob NOT NULL, \
dependants longblob \
)"
Sql.Sql db;
int have_dependants=0;
#if 0 // set to 1 to enable debugging
#ifdef debug
#undef debug
#endif // ifdef debug
#define debug(X...) werror("Cache.Storage.mysql: "+X);werror("\n")
#else // 1
#ifndef debug // if there's a clash, let's let it show
#define debug(X...) /**/
#endif // ifndef debug
#endif // 1
//! Database manipulation is done externally. This class only returns
//! values, with some lazy decoding.
class Data {
inherit Cache.Data;
private int _size;
private string db_data;
private mixed _data;
void create (mapping q) {
debug("instantiating data object from %O",q);
db_data=q->data;
_size=sizeof(db_data);
atime=(int)q->atime;
ctime=(int)q->ctime;
etime=(int)q->etime;
cost=(float)q->cost;
}
int size() {
debug("object size requested");
return _size;
}
mixed data() {
debug("data requested");
if (_data)
return _data;
debug("lazy-decoding data");
_data=decode_value(db_data);
db_data=0;
return _data;
}
}
//does MySQL support multiple outstanding resultsets?
//we'll know now.
//Notice: this will fail miserably with Sybase, for instance.
//Notice: can and will throw exceptions if anything fails.
private object(Sql.sql_result) enum_result;
int(0..0)|string first() {
debug("first()");
if (enum_result)
destruct(enum_result);
enum_result=db->big_query("select cachekey from cache");
return next();
}
int(0..0)|string next() {
debug("next()");
array res;
if (!enum_result)
return 0;
if (res=enum_result->fetch_row())
return res[0];
enum_result=0; // enumeration finished
return 0;
}
//unfortunately with MySQL we can't optimize much,
//if we want to properly follow the dependencies chain.
//also, we're taking the easy way out using encode_value rather than
// SQL tables. With other databases it would be easier to use
// SQL-related functions rather than doing stuff ourselves (and
// performing plenty of queries).
// I'll try to use a local cache to avoid multiple deletions for
// the same value, since queries are expensive. It could prove
// to be a problem for HUGE caches. Let's hope it won't happen..
void delete(string key, void|int(0..1) hard, void|multiset already_deleted) {
multiset dependants=0;
debug("deleting %s\n",key);
if (have_dependants) {
if (already_deleted && already_deleted[key]) // already deleted. Skip
return;
mixed rv=db->query("select dependants from cache where cachekey=%s",key);
if (rv && sizeof(rv) && rv[0]->dependants) { // there are dependants
dependants=decode_value(rv[0]->dependants);
}
if (!already_deleted) already_deleted=(<>);
}
if (already_deleted) already_deleted[key]=1;
db->query("delete from cache where cachekey=%s",key);
if (dependants) {
foreach (indices(dependants),string dep) {
werror("chain-deleting %s\n",dep);
delete(dep);
}
werror("done chain-deleting\n");
}
}
void set(string key, mixed value,
void|int expire_time, void|float preciousness,
void|multiset(string) dependants) {
debug("setting value for key %s (e: %d, v: %f",key,expire_time,
preciousness?preciousness:1.0);
db->query("delete from cache where cachekey=%s",key);
db->query("insert into cache "
"(cachekey,atime,ctime,etime,cost,data, dependants) "
"values(%s,CURRENT_TIMESTAMP,CURRENT_TIMESTAMP,%s,%s,%s,%s)",
key,
(expire_time?db->encode_datetime(expire_time):UNDEFINED),
(preciousness?(string)preciousness:"1"),
encode_value(value),
(dependants?encode_value(dependants):UNDEFINED)
//BUG: this fails when there are no dependants.
);
if (dependants)
have_dependants=1;
}
int(0..0)|Cache.Data get(string key,void|int notouch) {
debug("getting value for key %s (nt: %d)",key,notouch);
array(mapping) result=0;
mixed err=0;
catch (result=db->query("select unix_timestamp(atime) as atime,"
"unix_timestamp(ctime) as ctime,"
"unix_timestamp(etime) as etime,cost,data "
"from cache where cachekey=%s", key));
if (!result || !sizeof(result))
return 0;
if (!notouch)
catch(db->query("update cache set atime=CURRENT_TIMESTAMP "
"where cachekey=%s", key));
return Data(result[0]);
}
void aget(string key,
function(string,int(0..0)|Cache.Data:void) callback) {
callback(key,get(key));
}
//!
void create(string sql_url) {
array result=0;
mixed err=0;
db=Sql.Sql(sql_url);
// used to determine whether there already is a DB here.
err=catch(result=db->query("select stamp from cache_admin"));
if (err || !sizeof(result)) {
db->query(CREATION_QUERY);
db->query("create table cache_admin (stamp integer primary key)");
db->query("insert into cache_admin values ('1')");
}
}
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