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Major Description
ATS will generate a very large marshal header in a rare case. As we know, ATS will merge the response header if it get 304 from origin server. I found that the HdrHeap size will increase if duplidated header exist.
In our production environment, we got a response from origin server like this:
HTTP/1.1 200 OK
Content-Length: 60
...
Powered-By-CC: MISS from A
Cache-Control: public,max-age=0
Powered-By-CC: MISS from B
Connection: close
There is a duplicated header 'Powered-By-CC', and every time the doc had been accessed, ATS had to revalidate this doc from the origin as the max-age is 0. The origin server response 304 like this:
HTTP/1.1 304 Not Modified
...
Powered-By-CC: 8c61e322f02a0343e93ef227d82e5e0a
Cache-Control: public,max-age=0
Powered-By-CC: e4563610a50c63ed500d27bb5f1df848
Connection: close
ATS will merge the header frequently, and the HdrHeap size will increase endlessly.
Breakpoint 1, CacheVC::updateVector (this=0x14112f0) at CacheWrite.cc:132 132 header_len = write_vector->marshal_length(); (gdb) n 133 od->writing_vec = 1; (gdb) p header_len $1 = 1068944 (gdb) bt #0 CacheVC::updateVector (this=0x14112f0) at CacheWrite.cc:133 #1 0x00000000006c04c6 in CacheVC::openWriteClose (this=0x14112f0, event=0, e=0x0) at CacheWrite.cc:1276 #2 0x000000000069e827 in CacheVC::die (this=0x14112f0) at P_CacheInternal.h:738 #3 0x0000000000690b1f in CacheVC::do_io_close (this=0x14112f0, alerrno=-1) at Cache.cc:373 #4 0x00000000004fed48 in VConnection::do_io (this=0x14112f0, op=3, c=0x0, nbytes=9223372036854775807, cb=0x0, data=0) at ../iocore/eventsystem/P_VConnection.h:106 #5 0x0000000000591b5a in HttpCacheSM::close_write (this=0x7fffe7f7d3b0) at HttpCacheSM.h:118 #6 0x00000000005897a9 in HttpSM::issue_cache_update (this=0x7fffe7f7b980) at HttpSM.cc:5590 #7 0x00000000005895d6 in HttpSM::perform_cache_write_action (this=0x7fffe7f7b980) at HttpSM.cc:5540 #8 0x000000000058ef4d in HttpSM::set_next_state (this=0x7fffe7f7b980) at HttpSM.cc:7206 #9 0x000000000058e0be in HttpSM::call_transact_and_set_next_state (this=0x7fffe7f7b980, f=0) at HttpSM.cc:6962 #10 0x000000000057bedf in HttpSM::handle_api_return (this=0x7fffe7f7b980) at HttpSM.cc:1531 #11 0x00000000005944ca in HttpSM::do_api_callout (this=0x7fffe7f7b980) at HttpSM.cc:452 #12 0x000000000057cf73 in HttpSM::state_read_server_response_header (this=0x7fffe7f7b980, event=100, data=0x7fffe0015c78) at HttpSM.cc:1878 #13 0x000000000057f536 in HttpSM::main_handler (this=0x7fffe7f7b980, event=100, data=0x7fffe0015c78) at HttpSM.cc:2565 #14 0x00000000004f55a6 in Continuation::handleEvent (this=0x7fffe7f7b980, event=100, data=0x7fffe0015c78) at ../iocore/eventsystem/I_Continuation.h:146 #15 0x00000000006ead77 in read_signal_and_update (event=100, vc=0x7fffe0015b60) at UnixNetVConnection.cc:137 #16 0x00000000006eb5a7 in read_from_net (nh=0x7ffff37cea30, vc=0x7fffe0015b60, thread=0x7ffff37cb010) at UnixNetVConnection.cc:320 #17 0x00000000006ed221 in UnixNetVConnection::net_read_io (this=0x7fffe0015b60, nh=0x7ffff37cea30, lthread=0x7ffff37cb010) at UnixNetVConnection.cc:846 #18 0x00000000006e4dd1 in NetHandler::mainNetEvent (this=0x7ffff37cea30, event=5, e=0x1089e80) at UnixNet.cc:399 #19 0x00000000004f55a6 in Continuation::handleEvent (this=0x7ffff37cea30, event=5, data=0x1089e80) at ../iocore/eventsystem/I_Continuation.h:146 #20 0x000000000070bace in EThread::process_event (this=0x7ffff37cb010, e=0x1089e80, calling_code=5) at UnixEThread.cc:144 #21 0x000000000070bfd8 in EThread::execute (this=0x7ffff37cb010) at UnixEThread.cc:268 #22 0x0000000000526644 in main (argv=0x7fffffffe368) at Main.cc:1763
In HttpTransact::merge_response_header_with_cached_header(...), ATS will set the old MIMEField as DELETED if it is duplicated, and attach new MIMEField, this will increase the number of MIMEFieldBlockImpl, and the HdrHeap size may increase to larger than 1M.
I suggest to ignore the useless MIMEFieldBlockImpl when copy the MIME header in mime_hdr_copy_onto(...).