DLPX-99899 connstat-stats.sh: replace stdbuf -oL with mawk -W interactive

debian/control

@@ -13,6 +13,6 @@ Standards-Version: 4.1.2
 
 Package: performance-diagnostics
 Architecture: any
-Depends: python3-bpfcc, python3-minimal, python3-psutil, telegraf, docker-ce, influxdb2, curl, openssl, jq
+Depends: python3-bpfcc, python3-minimal, python3-psutil, telegraf, docker-ce, influxdb2, curl, openssl, jq, mawk
 Description: eBPF-based Performance Diagnostic Tools
   A collection of eBPF-based tools for diagnosing performance issues.

telegraf/connstat-stats.sh

@@ -16,13 +16,14 @@
 #   swnd, cwnd, rwnd, rtt                          (averaged across connections)
 #   connections                                    (count of aggregated conns)
 #
-# mawk (the default awk on Delphix engines) does not flush its stdout buffer
-# when writing to a Telegraf execd pipe, even with explicit fflush() calls.
-# stdbuf -oL forces line-buffered stdout on awk, so each output line is
-# delivered to Telegraf immediately without needing awk to exit.
+# mawk (the default awk on Delphix engines) reads a pipe in blocks: it keeps
+# reading until its 256 KB input buffer is full, or EOF, before processing any
+# record. connstat never exits and writes a few KB per interval, so plain mawk
+# prints nothing; stdbuf -oL and fflush() affect only output and don't help.
+# -W interactive makes mawk read stdin line by line (and unbuffers stdout).
 /usr/bin/connstat -PLe -i 10 -T u \
     -o laddr,lport,raddr,rport,inbytes,outbytes,retranssegs,suna,unsent,swnd,cwnd,rwnd,rtt \
-    | stdbuf -oL awk -F',' '
+    | /usr/bin/mawk -W interactive -F',' '
 BEGIN {
     batch_ts = 0
     # Load port->service mapping from /etc/services, same as LocalTCPStatsCollector.
@@ -53,7 +54,6 @@ BEGIN {
               inb[key] "," outb[key] "," ret[key] "," sun[key] "," uns[key] "," \
               int(sw[key]/n) "," int(cw[key]/n) "," int(rw[key]/n) "," int(rt[key]/n) "," n "," batch_ts
     }
-    fflush()
     ts = $0; sub(/^=[[:space:]]*/, "", ts); batch_ts = ts + 0
     delete cnt; delete inb; delete outb; delete ret
     delete sun; delete uns; delete sw; delete cw; delete rw; delete rt
@@ -81,6 +81,5 @@ END {
               inb[key] "," outb[key] "," ret[key] "," sun[key] "," uns[key] "," \
               int(sw[key]/n) "," int(cw[key]/n) "," int(rw[key]/n) "," int(rt[key]/n) "," n "," batch_ts
     }
-    fflush()
 }
 '