{173076598} sqlwriter: Reduce buffer to avoid heap fragmentation

Heap fragmentation was observed with slow clients, reading a large
number of small responses (comdb2del.tsk reading rowid and deleting rows
inline with the read operation.) This lead to sqlwriter repeatedly
buffering small payloads up to 1MB and consequently fragmenting the
heap.

Signed-off-by: Akshat Sikarwar <[email protected]>

net/sqlwriter.c

@@ -38,12 +38,7 @@ static struct timeval heartbeat_time = {.tv_sec = 0, .tv_usec = MSEC(100)};
 #define min_hb_time 1
 
 //writer will block if outstanding data hits:
-#define max_buf MB(1)
-
-//once blocked, writer drains to:
-#define resume_buf KB(128)
-
-BB_COMPILE_TIME_ASSERT(resume_max_buf, resume_buf < max_buf);
+#define max_buf KB(256)
 
 struct sqlwriter {
     struct sqlclntstate *clnt;
@@ -184,21 +179,17 @@ static void sql_flush_cb(int fd, short what, void *arg)
         UNLOCK_WR_LOCK_ONLY_IF_NOT_PACKING(writer);
         return;
     }
-    const int min = (writer->done || writer->flush) ? 0 : resume_buf;
-    while (1) {
+    while (outstanding) {
         if ((n = wr_evbuffer(writer, fd)) <= 0) {
             break;
         }
         writer->sent_at = time(NULL);
         outstanding -= n;
-        if (outstanding <= min) {
-            break;
-        }
     }
     if (n <= 0 && errno != EAGAIN && errno != EWOULDBLOCK) {
         writer->bad = 1;
         event_del(writer->flush_ev);
-    } else if (outstanding <= min) {
+    } else {
         sql_disable_flush(writer);
     }
     UNLOCK_WR_LOCK_ONLY_IF_NOT_PACKING(writer);