客户的问题是：
向Slony-I运行环境中，增加新的slaveDB节点的时候发生错误。
log中反复出现错误，然后再重新开始（重新开始部分的log省略）：
CONFIG remoteWorkerThread_1: connected to provider DB CONFIG remoteWorkerThread_1: prepare to copy table "tst"."a_tbl" CONFIG remoteWorkerThread_1: prepare to copy table "tst"."b_tbl" CONFIG remoteWorkerThread_1: prepare to copy table "tst"."c_tbl" CONFIG remoteWorkerThread_1: all tables for set 1 found on subscriber CONFIG remoteWorkerThread_1: copy sequence "tst"."a_no_seq" CONFIG remoteWorkerThread_1: copy sequence "tst"."b_no_seq" CONFIG remoteWorkerThread_1: copy sequence "tst"."c_no_seq" CONFIG remoteWorkerThread_1: copy table "tst"."a_tbl" CONFIG remoteWorkerThread_1: Begin COPY of table "tst"."a_tbl" NOTICE: truncate of "tst"."a_tbl" succeeded CONFIG remoteWorkerThread_1: 33778 bytes copied for table "tst"."a_tbl" CONFIG remoteWorkerThread_1: 27.97 seconds to copy table "tst"."a_tbl" CONFIG remoteWorkerThread_1: copy table "tst"."b_tbl" CONFIG remoteWorkerThread_1: Begin COPY of table "tst"."b_tbl" ERROR remoteWorkerThread_1: "select "_mycluster".copyFields(2);" WARN remoteWorkerThread_1: data copy for set 1 failed 1 times - sleep 15 seconds NOTICE: Slony-I: Logswitch to sl_log_2 initiated CONTEXT: SQL statement "SELECT "_mycluster".logswitch_start()"
经过查阅资料，并且和客户沟通，发现是他们的网络环境有问题：原有节点所在网段和新增节点不在一个网段。而他们又使用了网络工具来监控网络，在某些特定情况下，网络工具会切点网络连接。
正式此原因，导致出错。然后我进行了代码分析，发现remoteworker是很勤劳的，如果发生了通讯错误，它会反复重试的：
remoteWorkerThread_main函数的while循环，就会完成这个工作。
/* ----------
* slon_remoteWorkerThread
*
* Listen for events on the local database connection. This means, events
* generated by the local node only.
* ----------
*/
void *
remoteWorkerThread_main(void *cdata)
{
…
/*
* Work until shutdown or node destruction
*/
while (true)
{
…
/*
* Event type specific processing
*/
if (strcmp(event->ev_type, "SYNC") == 0)
{
…
}
else /* not SYNC */
{
…
/*
* Simple configuration events. Call the corresponding runtime
* config function, add the query to call the configuration event
* specific stored procedure.
*/
if (strcmp(event->ev_type, "STORE_NODE") == 0)
{
…
}
…
else if (strcmp(event->ev_type, "ENABLE_SUBSCRIPTION") == 0)
{
…
int copy_set_retries = 0;
…
if (sub_receiver == rtcfg_nodeid &&
event->ev_origin == node->no_id)
{
ScheduleStatus sched_rc;
int sleeptime = 15;
…
while (true)
{
…
/*
* If the copy succeeds, exit the loop and let the
* transaction commit.
*/
if (copy_set(node, local_conn, sub_set, event) == 0)
{
…
copy_set_retries = 0;
break;
}
copy_set_retries++;
/*
* Data copy for new enabled set has failed. Rollback
* the transaction, sleep and try again.
*/
slon_log(SLON_WARN, "remoteWorkerThread_%d: "
"data copy for set %d failed %d times - "
"sleep %d seconds\n",
node->no_id, sub_set, copy_set_retries,
sleeptime);
…
}
}
else
{
…
}
…
}
…
else
{
…
}
/*
* All simple configuration events fall through here. Commit the
* transaction.
*/
…
}
…
}
…
}
/* ----------
* copy_set
* ----------
*/
static int
copy_set(SlonNode *node, SlonConn *local_conn, int set_id,
SlonWorkMsg_event *event)
{
…
/*
* Connect to the provider DB
*/
…
slon_log(SLON_CONFIG, "remoteWorkerThread_%d: "
"connected to provider DB\n",
node->no_id);
…
/*
* For each table in the set
*/
for (tupno1 = 0; tupno1 < ntuples1; tupno1++)
{
char *tab_fqname = PQgetvalue(res1, tupno1, 1);
gettimeofday(&tv_start2, NULL);
slon_log(SLON_CONFIG, "remoteWorkerThread_%d: "
"prepare to copy table %s\n",
node->no_id, tab_fqname);
(void) slon_mkquery(&query3, "select * from %s limit 0;",
tab_fqname);
res2 = PQexec(loc_dbconn, dstring_data(&query3));
…
}
…
slon_log(SLON_CONFIG, "remoteWorkerThread_%d: "
"all tables for set %d found on subscriber\n",
node->no_id, set_id);
…
for (tupno1 = 0; tupno1 < ntuples1; tupno1++)
{
…
slon_log(SLON_CONFIG, "remoteWorkerThread_%d: "
"copy sequence %s\n",
node->no_id, seq_fqname);
…
}
…
/*
* For each table in the set
*/
for (tupno1 = 0; tupno1 < ntuples1; tupno1++)
{
…
slon_log(SLON_CONFIG, "remoteWorkerThread_%d: "
"copy table %s\n",
node->no_id, tab_fqname);
…
if (omit_copy) {
…
} else {
slon_log(SLON_CONFIG, "remoteWorkerThread_%d: "
"Begin COPY of table %s\n",
node->no_id, tab_fqname);
(void) slon_mkquery(&query2, "select %s.copyFields(%d);",
rtcfg_namespace, tab_id);
res3 = PQexec(pro_dbconn, dstring_data(&query2));
if (PQresultStatus(res3) != PGRES_TUPLES_OK)
{
slon_log(SLON_ERROR, "remoteWorkerThread_%d: \"%s\" %s\n",
node->no_id, dstring_data(&query2),
PQresultErrorMessage(res3));
…
return -1;
}
…
slon_log(SLON_CONFIG, "remoteWorkerThread_%d: "
INT64_FORMAT " bytes copied for table %s\n",
node->no_id, copysize, tab_fqname);
…
slon_log(SLON_CONFIG, "remoteWorkerThread_%d: "
"%.3f seconds to copy table %s\n",
node->no_id,
TIMEVAL_DIFF(&tv_start2, &tv_now), tab_fqname);
}
…
return 0;
}