Time out SUBSCRIBE query instead of forking.

sqlitecluster/SQLite.cpp

@@ -874,14 +874,19 @@ string SQLite::getCommittedHash() {
     return _sharedData.lastCommittedHash.load();
 }
 
-bool SQLite::getCommits(uint64_t fromIndex, uint64_t toIndex, SQResult& result) {
+int SQLite::getCommits(uint64_t fromIndex, uint64_t toIndex, SQResult& result, uint64_t timeoutLimitUS) {
     // Look up all the queries within that range
     SASSERTWARN(SWITHIN(1, fromIndex, toIndex));
     string query = _getJournalQuery({"SELECT id, hash, query FROM", "WHERE id >= " + SQ(fromIndex) +
                                     (toIndex ? " AND id <= " + SQ(toIndex) : "")});
     SDEBUG("Getting commits #" << fromIndex << "-" << toIndex);
     query = "SELECT hash, query FROM (" + query  + ") ORDER BY id";
-    return !SQuery(_db, "getting commits", query, result);
+    if (timeoutLimitUS) {
+        setTimeout(timeoutLimitUS);
+    }
+    int queryResult = SQuery(_db, "getting commits", query, result);
+    clearTimeout();
+    return queryResult;
 }
 
 int64_t SQLite::getLastInsertRowID() {

sqlitecluster/SQLite.h

@@ -221,7 +221,7 @@ class SQLite {
     static bool getCommit(sqlite3* db, const vector<string> journalNames, uint64_t index, string& query, string& hash);
 
     // Looks up a range of commits.
-    bool getCommits(uint64_t fromIndex, uint64_t toIndex, SQResult& result);
+    int getCommits(uint64_t fromIndex, uint64_t toIndex, SQResult& result, uint64_t timeoutLimitUS = 0);
 
     // Set a time limit for this transaction, in US from the current time.
     void setTimeout(uint64_t timeLimitUS);

sqlitecluster/SQLiteNode.cpp

@@ -1660,7 +1660,10 @@ void SQLiteNode::_onMESSAGE(SQLitePeer* peer, const SData& message) {
             }
             PINFO("Received SUBSCRIBE, accepting new follower");
             SData response("SUBSCRIPTION_APPROVED");
-            _queueSynchronize(this, peer, _db, response, true); // Send everything it's missing
+
+            // We send every remaining commit that the node doesn't have, but we set a timeout on the query that gathers these to half the
+            // maximum time limit that will cause this node to be disconnected from the cluster.
+            _queueSynchronize(this, peer, _db, response, true, RECV_TIMEOUT / 2);
             _sendToPeer(peer, response);
             SASSERTWARN(!peer->subscribed);
             peer->subscribed = true;
@@ -2083,7 +2086,7 @@ void SQLiteNode::_changeState(SQLiteNodeState newState, uint64_t commitIDToCance
     }
 }
 
-void SQLiteNode::_queueSynchronize(const SQLiteNode* const node, SQLitePeer* peer, SQLite& db, SData& response, bool sendAll) {
+void SQLiteNode::_queueSynchronize(const SQLiteNode* const node, SQLitePeer* peer, SQLite& db, SData& response, bool sendAll, uint64_t timeoutAfterUS) {
     // We need this to check the state of the node, and we also need `name` to make the logging macros work in a static
     // function. However, if you pass a null pointer here, we can't set these, so we'll fail. We also can't log that,
     // so we are just going to rely on the signal handling for sigsegv to log that for you. Don't do that.
@@ -2132,12 +2135,23 @@ void SQLiteNode::_queueSynchronize(const SQLiteNode* const node, SQLitePeer* pee
         // Figure out how much to send it
         uint64_t fromIndex = peerCommitCount + 1;
         uint64_t toIndex = targetCommit;
-        if (!sendAll)
+        if (sendAll) {
+            SINFO("Sending all commits with synchronize message, from " << fromIndex << " to " << toIndex); 
+        } else {
             toIndex = min(toIndex, fromIndex + 100); // 100 transactions at a time
-        if (!db.getCommits(fromIndex, toIndex, result))
-            STHROW("error getting commits");
-        if ((uint64_t)result.size() != toIndex - fromIndex + 1)
+        }
+        int resultCode = db.getCommits(fromIndex, toIndex, result, timeoutAfterUS);
+        if (resultCode) {
+            if (resultCode == SQLITE_INTERRUPT) {
+                STHROW("synchronization query timeout");
+            } else {
+                STHROW("error getting commits");
+            }
+        }
+
+        if ((uint64_t)result.size() != toIndex - fromIndex + 1) {
             STHROW("mismatched commit count");
+        }
 
         // Wrap everything into one huge message
         PINFO("Synchronizing commits from " << peerCommitCount + 1 << "-" << targetCommit);

sqlitecluster/SQLiteNode.h

@@ -216,7 +216,7 @@ class SQLiteNode : public STCPManager {
     // Queue a SYNCHRONIZE message based on the current state of the node, thread-safe, but you need to pass the
     // *correct* DB for the thread that's making the call (i.e., you can't use the node's internal DB from a worker
     // thread with a different DB object) - which is why this is static.
-    static void _queueSynchronize(const SQLiteNode* const node, SQLitePeer* peer, SQLite& db, SData& response, bool sendAll);
+    static void _queueSynchronize(const SQLiteNode* const node, SQLitePeer* peer, SQLite& db, SData& response, bool sendAll, uint64_t timeoutAfterUS = 0);
 
     bool _isNothingBlockingShutdown() const;
     bool _majoritySubscribed() const;