Berkeley DB示例程序详解(3.2)

/*
* Perform command line parsing and common replication setup for the repmgr
* and base replication example programs.
*/
int
common_rep_setup(dbenv, argc, argv, setup_info)
DB_ENV *dbenv;
int argc;
char *argv[];
SETUP_DATA *setup_info;
{
repsite_t site;
extern char *optarg;
char ch, *portstr;
int ack_policy, got_self, is_repmgr, maxsites, priority, ret;
got_self = is_repmgr = maxsites = ret = site.peer = 0;
/*
* 站点的优先级。在选举的时候，如果多个站点具有最新的日志，那么
* 优先级最高的站点成为master。所以，应该把后备做master的站点
* 设置更高的优先级。
*/
priority = 100;
/*
* 持久消息(permanent message, i.e. commit/abort/checkpoint日志)
* 确认策略。repmgr要求replica根据持久消息做相同的动作
* (commit/abort/checkpoint)，然后对持久消息进行确认。repmgr等待一定
* 数目的replica确认，这个数目字这里设置。
*/
ack_policy = DB_REPMGR_ACKS_QUORUM;
setup_info->role = UNKNOWN;
if (strncmp(setup_info->progname, "ex_rep_mgr", 10) == 0)
is_repmgr = 1;
/*
* Replication setup calls that are only needed if a command
* line option is specified are made within this while/switch
* statement. Replication setup calls that should be made
* whether or not a command line option is specified are after
* this while/switch statement.
*/
while ((ch = getopt(argc, argv, "a:bCh:l:Mn:p:R:r:v")) != EOF) {
switch (ch) {
case 'a':
if (!is_repmgr)
usage(is_repmgr, setup_info->progname);
if (strncmp(optarg, "all", 3) == 0)
ack_policy = DB_REPMGR_ACKS_ALL;
/* repmgr等待所有站点的持久消息确认。*/
else if (strncmp(optarg, "quorum", 6) != 0)
usage(is_repmgr, setup_info->progname);
break;
case 'b':
/*
* 批量传输设置。在bulk buffer满了或者有了持久消息
* (permanent message)的时候才传输所有的消息。
* Configure bulk transfer to send groups of records
* to clients in a single network transfer. This is
* useful for master sites and clients participating
* in client-to-client synchronization.
*/
if ((ret = dbenv->rep_set_config(dbenv,
DB_REP_CONF_BULK, 1)) != 0) {
dbenv->err(dbenv, ret,
"Could not configure bulk transfer./n");
goto err;
}
break;
case 'C':
setup_info->role = CLIENT;
break;
case 'h':
setup_info->home = optarg;
break;
case 'l':
setup_info->self.host = strtok(optarg, ":");
if ((portstr = strtok(NULL, ":")) == NULL) {
fprintf(stderr, "Bad host specification./n");
goto err;
}
setup_info->self.port = (unsigned short)atoi(portstr);
setup_info->self.peer = 0;
got_self = 1;
break;
case 'M':
setup_info->role = MASTER;
break;
case 'n':
setup_info->nsites = atoi(optarg);
/*
* For repmgr, set the total number of sites in the
* replication group. This is used by repmgr internal
* election processing. For base replication, nsites
* is simply passed back to main for use in its
* communications and election processing.
*/
if (is_repmgr && setup_info->nsites > 0 &&
(ret = dbenv->rep_set_nsites(dbenv,
setup_info->nsites)) != 0) {
dbenv->err(dbenv, ret,
"Could not set nsites./n");
goto err;
}
break;
case 'p':
priority = atoi(optarg);
break;
case 'R':
if (!is_repmgr)
usage(is_repmgr, setup_info->progname);
site.peer = 1; /* FALLTHROUGH */
case 'r':
site.host = optarg;
site.host = strtok(site.host, ":");
if ((portstr = strtok(NULL, ":")) == NULL) {
fprintf(stderr, "Bad host specification./n");
goto err;
}
site.port = (unsigned short)atoi(portstr);
if (setup_info->site_list == NULL ||
setup_info->remotesites >= maxsites) {
maxsites = maxsites == 0 ? 10 : 2 * maxsites;
if ((setup_info->site_list =
realloc(setup_info->site_list,
maxsites * sizeof(repsite_t))) == NULL) {
fprintf(stderr, "System error %s/n",
strerror(errno));
goto err;
}
}
(setup_info->site_list)[(setup_info->remotesites)++] =
site;
site.peer = 0;
break;
case 'v':
if ((ret = dbenv->set_verbose(dbenv,
DB_VERB_REPLICATION, 1)) != 0)
goto err;
break;
case '?':
default:
usage(is_repmgr, setup_info->progname);
}
}
/* Error check command line. */
if (!got_self || setup_info->home == NULL)
usage(is_repmgr, setup_info->progname);
if (!is_repmgr && setup_info->role == UNKNOWN) {
fprintf(stderr, "Must specify -M or -C./n");
goto err;
}
/*
* Set replication group election priority for this environment.
* An election first selects the site with the most recent log
* records as the new master. If multiple sites have the most
* recent log records, the site with the highest priority value
* is selected as master.
*/
if ((ret = dbenv->rep_set_priority(dbenv, priority)) != 0) {
dbenv->err(dbenv, ret, "Could not set priority./n");
goto err;
}
/*
* 设置持久消息确认策略。
* For repmgr, set the policy that determines how master and client
* sites handle acknowledgement of replication messages needed for
* permanent records. The default policy of "quorum" requires only
* a quorum of electable peers sufficient to ensure a permanent
* record remains durable if an election is held. The "all" option
* requires all clients to acknowledge a permanent replication
* message instead.
*/
if (is_repmgr &&
(ret = dbenv->repmgr_set_ack_policy(dbenv, ack_policy)) != 0) {
dbenv->err(dbenv, ret, "Could not set ack policy./n");
goto err;
}
/*
* Set the threshold for the minimum and maximum time the client
* waits before requesting retransmission of a missing message.
* Base these values on the performance and load characteristics
* of the master and client host platforms as well as the round
* trip message time.
* 设置丢失的日志消息的重传时限。如果Berkeley DB发现有日志消息丢失，
* 比如它发现连续收到的两条日志消息并不连续，它会在等待20秒后请求
* 重传这条日志消息，如果仍然没有收到，它会加倍等待的时间，直到该
* 等待时间达到500秒。
*
* 在使用repmgr的时候，由于使用了TCP/IP协议，不可能丢失消息，
* 所以可以不设置；如果使用不可靠的传输协议比如udp，那么可以通过
* 设置这个时限，确保能够收到丢失的日志消息。也就是说，Berkeley DB
* 内部实现了一个确保不可靠传输协议可靠地传输数据的协议，这样如果
* 我们使用UDP协议来传输Berkeley DB replication消息，那么丢包和
* 包错序不会影响Berkeley DB replication 的正常工作。
*/
if ((ret = dbenv->rep_set_request(dbenv, 20000, 500000)) != 0) {
dbenv->err(dbenv, ret,
"Could not set client_retransmission defaults./n");
goto err;
}
/*
* Configure deadlock detection to ensure that any deadlocks
* are broken by having one of the conflicting lock requests
* rejected. DB_LOCK_DEFAULT uses the lock policy specified
* at environment creation time or DB_LOCK_RANDOM if none was
* specified.
*/
if ((ret = dbenv->set_lk_detect(dbenv, DB_LOCK_DEFAULT)) != 0) {
dbenv->err(dbenv, ret,
"Could not configure deadlock detection./n");
goto err;
}
/* The following base replication features may also be useful to your
* application. See Berkeley DB documentation for more details.
* - Master leases: Provide stricter consistency for data reads
* on a master site.
* - Timeouts: Customize the amount of time Berkeley DB waits
* for such things as an election to be concluded or a master
* lease to be granted.
* - Delayed client synchronization: Manage the master site's
* resources by spreading out resource-intensive client
* synchronizations.
* - Blocked client operations: Return immediately with an error
* instead of waiting indefinitely if a client operation is
* blocked by an ongoing client synchronization.
*/
err:
return (ret);
}
static int
print_stocks(dbp)
DB *dbp;
{
DBC *dbc;
DBT key, data;
#define MAXKEYSIZE 10
#define MAXDATASIZE 20
char keybuf[MAXKEYSIZE + 1], databuf[MAXDATASIZE + 1];
int ret, t_ret;
u_int32_t keysize, datasize;
/* 读取数据，打印数据库当中所有记录。这个函数可以在master和每一个
* replica上面执行。*/
if ((ret = dbp->cursor(dbp, NULL, &dbc, 0)) != 0) {
dbp->err(dbp, ret, "can't open cursor");
return (ret);
}
memset(&key, 0, sizeof(key));
memset(&data, 0, sizeof(data));
printf("/tSymbol/tPrice/n");
printf("/t======/t=====/n");
/* 无论master上面还是replica上面，都是用完全相同的方法读取数据。*/
for (ret = dbc->get(dbc, &key, &data, DB_FIRST);
ret == 0;
ret = dbc->get(dbc, &key, &data, DB_NEXT)) {
keysize = key.size > MAXKEYSIZE ? MAXKEYSIZE : key.size;
memcpy(keybuf, key.data, keysize);
keybuf[keysize] = '/0';
datasize = data.size >= MAXDATASIZE ? MAXDATASIZE : data.size;
memcpy(databuf, data.data, datasize);
databuf[datasize] = '/0';
printf("/t%s/t%s/n", keybuf, databuf);
}
printf("/n");
fflush(stdout);
if ((t_ret = dbc->close(dbc)) != 0 && ret == 0)
ret = t_ret;
switch (ret) {
case 0:
case DB_NOTFOUND:
case DB_LOCK_DEADLOCK:
return (0);
default:
return (ret);
}
}
/* Start checkpoint and log archive support threads. */
int
start_support_threads(dbenv, sup_args, ckp_thr, lga_thr)
DB_ENV *dbenv;
supthr_args *sup_args;
thread_t *ckp_thr;
thread_t *lga_thr;
{
int ret;
ret = 0;
if ((ret = thread_create(ckp_thr, NULL, checkpoint_thread,
sup_args)) != 0) {
dbenv->errx(dbenv, "can't create checkpoint thread");
goto err;
}
if ((ret = thread_create(lga_thr, NULL, log_archive_thread,
sup_args)) != 0)
dbenv->errx(dbenv, "can't create log archive thread");
err:
return (ret);
}
/* Wait for checkpoint and log archive support threads to finish. */
int
finish_support_threads(ckp_thr, lga_thr)
thread_t *ckp_thr;
thread_t *lga_thr;
{
void *ctstatus, *ltstatus;
int ret;
ret = 0;
if (thread_join(*lga_thr, <status) ||
thread_join(*ckp_thr, &ctstatus)) {
ret = -1;
goto err;
}
if ((uintptr_t)ltstatus != EXIT_SUCCESS ||
(uintptr_t)ctstatus != EXIT_SUCCESS)
ret = -1;
err:
return (ret);
}
#define BUFSIZE 1024
int
doloop(dbenv, shared_data)
DB_ENV *dbenv;
SHARED_DATA *shared_data;
{
DB *dbp;
DBT key, data;
char buf[BUFSIZE], *first, *price;
u_int32_t flags;
int ret;
dbp = NULL;
ret = 0;
memset(&key, 0, sizeof(key));
memset(&data, 0, sizeof(data));
for (;;) {
printf("QUOTESERVER%s> ",
shared_data->is_master ? "" : " (read-only)");
fflush(stdout);
if (fgets(buf, sizeof(buf), stdin) == NULL)
break;
#define DELIM " /t/n"
if ((first = strtok(&buf[0], DELIM)) == NULL) {
/* Blank input line. */
price = NULL;
} else if ((price = strtok(NULL, DELIM)) == NULL) {
/* Just one input token. */
if (strncmp(buf, "exit", 4) == 0 ||
strncmp(buf, "quit", 4) == 0) {
/*
* This makes the checkpoint and log
* archive threads stop.
*/
shared_data->app_finished = 1;
break;
}
dbenv->errx(dbenv, "Format: TICKER VALUE");
continue;
} else {
/* Normal two-token input line. */
if (first != NULL && !shared_data->is_master) {
dbenv->errx(dbenv, "Can't update at client");
continue;
}
}
if (dbp == NULL) {
if ((ret = db_create(&dbp, dbenv, 0)) != 0)
return (ret);
flags = DB_AUTO_COMMIT;
/*
* Open database with DB_CREATE only if this is
* a master database. A client database uses
* polling to attempt to open the database without
* DB_CREATE until it is successful. 由于数据库
* 的创建也是一个写入操作，所以，replica不应该自
* 己创建数据库，而是定期检查是否有数据库被创建
* 好。当master创建了数据库后，这个日志消息会到
* 达所有的replica上面，于是Berkeley DB的
* replication功能自动创建好这个数据库。
*
* This DB_CREATE polling logic can be simplified
* under some circumstances. For example, if the
* application can be sure a database is already
* there, it would never need to open it with
* DB_CREATE.
*/
if (shared_data->is_master)
flags |= DB_CREATE;
if ((ret = dbp->open(dbp,
NULL, DATABASE, NULL, DB_BTREE, flags, 0)) != 0) {
if (ret == ENOENT) {
printf(
"No stock database yet available./n");
if ((ret = dbp->close(dbp, 0)) != 0) {
dbenv->err(dbenv, ret,
"DB->close");
goto err;
}
dbp = NULL;
continue;
}
if (ret == DB_REP_HANDLE_DEAD ||
ret == DB_LOCK_DEADLOCK) {
dbenv->err(dbenv, ret,
"please retry the operation");
dbp->close(dbp, DB_NOSYNC);
dbp = NULL;
continue;
}
dbenv->err(dbenv, ret, "DB->open");
goto err;
}
}
if (first == NULL) {
/*
* If this is a client in the middle of
* synchronizing with the master, the client data
* is possibly stale and won't be displayed until
* client synchronization is finished. It is also
* possible to display the stale data if this is
* acceptable to the application.
*/
if (shared_data->in_client_sync)
printf(
"Cannot read data during client synchronization - please try again./n");
else
switch ((ret = print_stocks(dbp))) {
case 0:
break;
case DB_REP_HANDLE_DEAD:
(void)dbp->close(dbp, DB_NOSYNC);
dbp = NULL;
break;
default:
dbp->err(dbp, ret,
"Error traversing data");
goto err;
}
} else {
key.data = first;
key.size = (u_int32_t)strlen(first);
data.data = price;
data.size = (u_int32_t)strlen(price);
if ((ret = dbp->put(dbp,
NULL, &key, &data, DB_AUTO_COMMIT)) != 0) {
dbp->err(dbp, ret, "DB->put");
goto err;
}
}
}
err: if (dbp != NULL)
(void)dbp->close(dbp, DB_NOSYNC);
return (ret);
}
int
create_env(progname, dbenvp)
const char *progname;
DB_ENV **dbenvp;
{
DB_ENV *dbenv;
int ret;
if ((ret = db_env_create(&dbenv, 0)) != 0) {
fprintf(stderr, "can't create env handle: %s/n",
db_strerror(ret));
return (ret);
}
dbenv->set_errfile(dbenv, stderr);
dbenv->set_errpfx(dbenv, progname);
*dbenvp = dbenv;
return (0);
}
/* Open and configure an environment. */
int
env_init(dbenv, home)
DB_ENV *dbenv;
const char *home;
{
u_int32_t flags;
int ret;
(void)dbenv->set_cachesize(dbenv, 0, CACHESIZE, 0);
(void)dbenv->set_flags(dbenv, DB_TXN_NOSYNC, 1);
flags = DB_CREATE | DB_INIT_LOCK | DB_INIT_LOG | DB_INIT_MPOOL |
DB_INIT_REP | DB_INIT_TXN | DB_RECOVER | DB_THREAD;
if ((ret = dbenv->open(dbenv, home, flags, 0)) != 0)
dbenv->err(dbenv, ret, "can't open environment");
return (ret);
}
/*
* In this application, we specify all communication via the command line. In
* a real application, we would expect that information about the other sites
* in the system would be maintained in some sort of configuration file. The
* critical part of this interface is that we assume at startup that we can
* find out
* 1) what host/port we wish to listen on for connections,
* 2) a (possibly empty) list of other sites we should attempt to connect
* to; and
* 3) what our Berkeley DB home environment is.
*
* These pieces of information are expressed by the following flags.
* -a all|quorum (optional; repmgr only, a stands for ack policy)
* -b (optional, b stands for bulk)
* -C or -M start up as client or master (optional for repmgr, required
* for base example)
* -h home directory (required)
* -l host:port (required; l stands for local)
* -n nsites (optional; number of sites in replication group; defaults to 0
* in which case we try to dynamically compute the number of sites in
* the replication group)
* -p priority (optional: defaults to 100)
* -r host:port (optional; r stands for remote; any number of these may be
* specified)
* -R host:port (optional; repmgr only, remote peer)
* -v (optional; v stands for verbose)
*/
void
usage(is_repmgr, progname)
const int is_repmgr;
const char *progname;
{
fprintf(stderr, "usage: %s ", progname);
if (is_repmgr)
fprintf(stderr, "[-CM]-h home -l host:port[-r host:port]%s%s",
"[-R host:port][-a all|quorum][-b][-n nsites]",
"[-p priority][-v]/n");
else
fprintf(stderr, "-CM -h home -l host:port[-r host:port]%s",
"[-b][-n nsites][-p priority][-v]/n");
exit(EXIT_FAILURE);
}
/*
* This is a very simple thread that performs checkpoints at a fixed
* time interval. For a master site, the time interval is one minute
* plus the duration of the checkpoint_delay timeout (30 seconds by
* default.) For a client site, the time interval is one minute.
*/
void *
checkpoint_thread(args)
void *args;
{
DB_ENV *dbenv;
SHARED_DATA *shared;
supthr_args *ca;
int i, ret;
ca = (supthr_args *)args;
dbenv = ca->dbenv;
shared = ca->shared;
for (;;) {
/*
* Wait for one minute, polling once per second to see if
* application has finished. When application has finished,
* terminate this thread.
*/
for (i = 0; i < 60; i++) {
sleep(1);
if (shared->app_finished == 1)
return ((void *)EXIT_SUCCESS);
}
/* Perform a checkpoint. */
if ((ret = dbenv->txn_checkpoint(dbenv, 0, 0, 0)) != 0) {
dbenv->err(dbenv, ret,
"Could not perform checkpoint./n");
return ((void *)EXIT_FAILURE);
}
}
}
/*
* This is a simple log archive thread. Once per minute, it removes all but
* the most recent 3 logs that are safe to remove according to a call to
* DB_ENV->log_archive().
*
* Log cleanup is needed to conserve disk space, but aggressive log cleanup
* can cause more frequent client initializations if a client lags too far
* behind the current master. This can happen in the event of a slow client,
* a network partition, or a new master that has not kept as many logs as the
* previous master.
*
* The approach in this routine balances the need to mitigate against a
* lagging client by keeping a few more of the most recent unneeded logs
* with the need to conserve disk space by regularly cleaning up log files.
* Use of automatic log removal (DB_ENV->log_set_config() DB_LOG_AUTO_REMOVE
* flag) is not recommended for replication due to the risk of frequent
* client initializations.
*/
void *
log_archive_thread(args)
void *args;
{
DB_ENV *dbenv;
SHARED_DATA *shared;
char **begin, **list;
supthr_args *la;
int i, listlen, logs_to_keep, minlog, ret;
la = (supthr_args *)args;
dbenv = la->dbenv;
shared = la->shared;
logs_to_keep = 3;
for (;;) {
/*
* Wait for one minute, polling once per second to see if
* application has finished. When application has finished,
* terminate this thread.
*/
for (i = 0; i < 60; i++) {
sleep(1);
if (shared->app_finished == 1)
return ((void *)EXIT_SUCCESS);
}
/* Get the list of unneeded log files. */
if ((ret = dbenv->log_archive(dbenv, &list, DB_ARCH_ABS))
!= 0) {
dbenv->err(dbenv, ret,
"Could not get log archive list.");
return ((void *)EXIT_FAILURE);
}
if (list != NULL) {
listlen = 0;
/* Get the number of logs in the list. */
for (begin = list; *begin != NULL; begin++, listlen++);
/*
* Remove all but the logs_to_keep most recent
* unneeded log files.
*/
minlog = listlen - logs_to_keep;
for (begin = list, i= 0; i < minlog; list++, i++) {
if ((ret = unlink(*list)) != 0) {
dbenv->err(dbenv, ret,
"logclean: remove %s", *list);
dbenv->errx(dbenv,
"logclean: Error remove %s", *list);
free(begin);
return ((void *)EXIT_FAILURE);
}
}
free(begin);
}
}
}

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