> Dear MIDAS experts,
> 
> when I attempted to increase the max number of hotlinks in ODB , defined as 
> 
> #define MAX_OPEN_RECORDS       256           /**< number of open DB records   */
> 
> I started running into an assertion in midas/src/odb.cxx
> 
> https://bitbucket.org/tmidas/midas/src/fa5457b5274a6b42c5ed8b6dea5e3cdd43de38fe/src/odb.cxx#lines-1525 :
> 
>   assert(sizeof(DATABASE_CLIENT) == 2112);
> 
> is it possible that the size of the DATABASE_CLIENT structure should be checked against 64+sizeof(OPEN_RECORD)*MAX_OPEN_RECORDS ?
> - 64 clearly can be expressed in a better maintainable form

Yes, this assert needs to be updated if you increase MAX_OPEN_RECORDS. See 
https://daq00.triumf.ca/MidasWiki/index.php/FAQ#Increasing_Number_of_Hot-links

> UPDATE: similar consideration holds for the size of the DATABLE_HEADER structure, which is also checked against a constant
> 
> https://bitbucket.org/tmidas/midas/src/fa5457b5274a6b42c5ed8b6dea5e3cdd43de38fe/src/odb.cxx#lines-1526

Yes DATABASE_HEADER can also be updated, but the associated assert()s need to be updated too.

FYI I have done both of these things and have attached patches.

Cheers,

Nick.

From 6ac1ad23e1e0c8fcfdbb25844ace9de3ab7a993b Mon Sep 17 00:00:00 2001
From: Nick Hastings <hastings@post.kek.jp>
Date: Tue, 19 Sep 2023 08:57:11 +0900
Subject: [PATCH 1/2] Increase MAX_OPEN_RECORDS to increase the max number of
 hot_links

In 2011 the number of hotlinks for the gsc was increased from the
default 256 to 2560. See https://elog.nd280.org/elog/GSC/425. Since we
are getting more equipment, increase to 4096. General
instructions can be found on the midas wiki at.
https://daq00.triumf.ca/MidasWiki/index.php/FAQ#Increasing_Number_of_Hot-links

When increasing this number the size of two structs will also
increase. Midas checks the size of these structs are correct, so
updated the check sizes.

DATABASE_CLIENT = 64 + 8*MAX_OPEN_ERCORDS

default:        = 64 + 8*256
                = 2112  -> Confirmed in odb.cxx

updated:        = 64 + 8*4096
                = 32832

DATABASE_HEADER = 64 + 64*DATABASE_CLIENT

default:        = 64 + 64*2112
                = 135232 -> Confirmed in odb.cxx

updated:        = 64 + 64*32832
                = 2101312
---
 include/midas.h | 2 +-
 src/odb.cxx     | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/midas.h b/include/midas.h
index ec6b54a1..46d653f4 100644
--- a/include/midas.h
+++ b/include/midas.h
@@ -273,7 +273,7 @@ class MJsonNode; // forward declaration from mjson.h
 #define HOST_NAME_LENGTH       256           /**< length of TCP/IP names      */
 #define MAX_CLIENTS            64            /**< client processes per buf/db */
 #define MAX_EVENT_REQUESTS     10            /**< event requests per client   */
-#define MAX_OPEN_RECORDS       256           /**< number of open DB records   */
+#define MAX_OPEN_RECORDS       4096          /**< number of open DB records   */
 #define MAX_ODB_PATH           256           /**< length of path in ODB       */
 #define BANKLIST_MAX           4096          /**< max # of banks in event     */
 #define STRING_BANKLIST_MAX    BANKLIST_MAX * 4   /**< for bk_list()          */
diff --git a/src/odb.cxx b/src/odb.cxx
index e4e2bd35..bc084612 100644
--- a/src/odb.cxx
+++ b/src/odb.cxx
@@ -1477,8 +1477,8 @@ static void db_validate_sizes()
    assert(sizeof(KEY) == 68);
    assert(sizeof(KEYLIST) == 12);
    assert(sizeof(OPEN_RECORD) == 8);
-   assert(sizeof(DATABASE_CLIENT) == 2112);
-   assert(sizeof(DATABASE_HEADER) == 135232);
+   assert(sizeof(DATABASE_CLIENT) == 32832);
+   assert(sizeof(DATABASE_HEADER) == 2101312);
    assert(sizeof(EVENT_HEADER) == 16);
    //assert(sizeof(EQUIPMENT_INFO) == 696); has been moved to dynamic checking inside mhttpd.c
    assert(sizeof(EQUIPMENT_STATS) == 24);
-- 
2.47.3