History System: Difference between revisions

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== Links ==
The midas documentation has moved. The new documentation about the history system is in:
<div style="column-count:3;-moz-column-count:3;-webkit-column-count:3">
* [https://midas.triumf.ca/docs/develop/features/storing_data/history/ History: overview] (what the history system records and how to view it)
* [[/History ODB tree]]
* [https://midas.triumf.ca/docs/develop/features/storing_data/history/configuring/ History: configuring] (what gets recorded, history drivers and SQL databases)
* [[mhttpd]] history page
* [https://midas.triumf.ca/docs/develop/features/storing_data/history/programming/ History: programming] (event and tag names, code interfaces)
* [[Mhformat|history format]] &rarr; 
* [https://midas.triumf.ca/docs/develop/reference/reference/history_formats/ History file formats and database schema] (file formats and SQL table layout)
* [[Keys in the ODB /Logger tree|/Logger ODB tree]]
* [[Keys in the ODB /Logger/History subtree|/Logger/History subtree]]
*
</div>
 
= Introduction =
 
The history system is an add-on capability built into the MIDAS data logger [[mlogger]] to record useful information in parallel to the data logging.
This information is recorded with a time stamp and saved into a history file  (see [[#History drivers|History drivers]]) for later retrieval. One set of files is created per day containing all the requested history events. The history data may be displayed in graphical form using the [[mhttpd]] MIDAS webserver utility, giving the user an easy way of seeing how experimental variables have changed with time.
The history logging will be in action only if the MIDAS data logger is running, but it is not necessary to have any [[Keys in the ODB /Logger tree#/Logger/Channels subtree|data logging channel]] enabled.
 
= MidasHistoryInterface =
 
New history configuration defines history channels similar to logger channels. Each history channel creates a history interface class (class MidasHistoryInterface). The mlogger can use this interface to write data into the history, mhttpd, mhist & co can use this interface to read data from the history. The interface is defined in history.h
 
* http://ladd00.triumf.ca/~daqweb/doc/midas/include/history.h
 
= History drivers =
 
The MIDAS distribution contains these drivers:
 
; MIDAS history
: the traditional MIDAS history, data is stored in the .hst binary files. (format is documented here [[mhformat]], see also [[mhist]] and [[mhdump]])
: By default ODB subtree '''[[Keys in the ODB /Logger/History subtree#/Logger/History/0/ subtree |history channel 0]]''' is set up to write '''MIDAS''' history.
 
; ODBC history 
: stores history data in SQL database using the ODBC abstraction layer. See [[#MIDAS ODBC API SQL History system|ODBC SQL History system]].
 
: By default ODB subtree '''[[Keys in the ODB /Logger/History subtree#/Logger/History/1/ subtree |history channel 1]]'''  is set up to write '''ODBC''' history.
 
; SQLITE history
: stores data in SQL database as SQLITE3 .sqlite3 files. The SQL table format is similar to ODBC history, performance is similar, no database server required.
: By default '''[[Keys in the ODB /Logger/History subtree#/Logger/History/0/ subtree |history channel 2]]'''  is set up to write '''SQLITE''' history.
 
 
More drivers can be easily added by the user (create history_xxx.cxx, add constructor to hs_get_history(), create the ODB subtree  <span style="color:purple; font-style:italic">/Logger/History/x/channel</span>).
 
= Location of History Files =
 
By default, the traditional MIDAS history is enabled, writing history files into the MIDAS data directory path given by the ODB key [[Keys in the ODB /Logger tree#Data dir|Data dir]].
If history data is important, it is recommended to write it to a directory that is backed up or archived. (The MIDAS data directory is usually located on a scratch data disk without backups).
The location of the MIDAS history data files can be changed by use of the ODB Key
[[Keys in the ODB /Logger tree#History dir|History dir]].
 
= Types of History Events =
 
There are two basic types of history events, which are defined in different ways:
 
*    "[[#Frontend History Event|Frontend]]" History event composed in the frontend. See [[#Frontend History Event|Frontend History Event]] for details.
*    "Virtual" History event composed within the ODB under the  [[/History ODB tree#Links subtree|/History/Links subtree]].
 
 
Both these history event definitions take effect when the data logger gets a start run [[Run States and Transitions|transition]]. Any modifications made during the run are not applied until the start of the next run.
 
 
 
= Frontend History Event =
 
Each  [[Frontend Operation#Equipments and Events|Equipment]] has the capability to generate "history data".
 
== To enable Frontend History Events ==
 
* Set the [[/Equipment ODB tree#Log history|Log history]] key of each equipment to be logged non-zero. This causes the event contents to be copied to the  ODB [[/Equipment ODB tree#Variables subtree|/Equipment/''<equipment-name>''/Variables subtree]] for the use of the History system .
 
* Set the [[/Equipment ODB tree#Log history|Log history]] key of each equipment to be logged non-zero (see [[Equipment List Parameters#Log History|Log History parameter]]. You may need to restart the frontend. This causes the event contents to be copied to the  ODB [[/Equipment ODB tree#Variables subtree|/Equipment/''<equipment-name>''/Variables subtree]] for the use of the History system.
 
* Select the  '''[[#History drivers|history driver]]''' and therefore '''history channel'''  to use to write the MIDAS history files.
* set [[Keys in the ODB /Logger/History subtree|Active]] ODB key in the selected [[#History drivers|History channel]] to "y"
* set [[/History ODB tree#LoggerHistoryChannel|LoggerHistoryChannel]] to the selected [[#History drivers|History channel]]
 
=== To write MIDAS Frontend History  ===
 
* Perform steps in [[#To write a Frontend History Event]] above
* The  '''[[#History drivers|history driver]]''' is MIDAS and therefore '''history channel''' (default is "0") to use to write the MIDAS history files.
* set [[Keys in the ODB /Logger/History subtree#/Logger/History/0/Active|Active]] ODB key in the selected to "y"
* set [[/History ODB tree#LoggerHistoryChannel|LoggerHistoryChannel]] to the selected [[#History drivers|History channel]] (default 0)
* restart [[mhttpd]] and [[mlogger]], start the run.
 
MIDAS History files will be saved into the  [[#Location of History Files|history data directory]].
 
=== To write ODBC Frontend History  ===
 
See [[#MIDAS ODBC SQL History system]]
* If necessary, [[Set up a MySQL database#Set up a MySQL database]].
* Perform steps in [[#To write a Frontend History Event]] above
* The  '''[[#History drivers|history driver]]''' is MIDAS and therefore '''history channel''' (default is "1") to use to write the ODBC history files.
* set [[Keys in the ODB /Logger/History subtree#/Logger/History/1/Active|Active]] ODB key to "y"
* set ODB key [[/History ODB tree#LoggerHistoryChannel|LoggerHistoryChannel]] to the selected [[#History drivers|History channel]] (default 1)
* Check ODB Key[[Keys in the ODB /Logger/History subtree#/Logger/History/1/Writer_ODBC_DSN|Writer_ODBC_DSN]] is set to "history writer" and Key
[[Keys in the ODB /Logger/History subtree#/Logger/History/1/Reader_ODBC_DSN|Reader_ODBC_DSN]]
is set to "history reader" (the default values)
* set [[Keys in the ODB /Logger/History subtree#/Logger/History/1/Debug|Debug]] to 1 if desired
* restart [[mlogger]] in verbose mode (i.e. mlogger -v), and observe how it issues SQL commands to create the tables and columns corresponding to MIDAS history events and tags.
** [[mlogger]] is programmed to raise alarms if connection to SQL database is interrupted or if some events cannot be written into the database (i.e. data type mismatch, SQL syntax errors, etc). The traditional MIDAS history never raised alarms because it "never failed" - other than from "disk full" errors, which are immediately obvious.
 
* restart [[mhttpd]]
** With ODBC History enabled, [[mhttpd]] will only use history information from the SQL database to make history plots and to extract history variable names for the history plot editor. The ODB /History [[/History ODB tree#Tags subtree|Tags]] and
[[/History ODB tree#Events subtree|Events]] subtrees  are not used.
 
** variable names presented to the user may change from MIDAS names to SQL names (use the history panel "Label" text fields to create permanent plot labels).
 
 
 
=== To write  SQLITE Frontend history  ===
No special configuration required.
 
* Perform steps in [[#To write a Frontend History Event]] above
* The  '''[[#History drivers|history driver]]''' is SQLITE and therefore '''history channel''' (default is "2") to use to write the SQLITE history files.
* set [[Keys in the ODB /Logger/History subtree#/Logger/History/1/Active|Active]] ODB key to "y"
* set ODB key [[/History ODB tree#LoggerHistoryChannel|LoggerHistoryChannel]] to the selected [[#History drivers|History channel]] (default 2)
* Create a directory for storage of sqlite history files
* save its path in the ODB key  [[Keys in the ODB /Logger/History subtree#/Logger/History/1/Sqlite|Sqlite dir]]
* restart [[mhttpd]] and [[mlogger]]
 
In the history data directory (in [[Keys in the ODB /Logger/History subtree#/Logger/History/1/Sqlite|Sqlite dir]]) you should see files with name "mh_xxx.sqlite3" corresponding to your equipment and variable names.
 
 
 
== Data path for frontend History Event ==
The main data path for the frontend History Event is as follows:
 
* The user code in the frontend equipment Event Readout routines reads the data, placing it into a MIDAS data bank
* In mfe.c, if the key [[/Equipment ODB tree#Log history|Log history]] > 0 (i.e. the history system is enabled for this equipment), this data bank is written into ODB (by update_odb()).
* This ODB write triggers an ODB hot-link into mlogger
* The hot-link calls mlogger.c::log_history(), which calls hs_write() to write the data into the history file. The frequency of the history writes is specified by the number of seconds between writes stored in the ODB key [[/Equipment ODB tree#Log history|Log history]].
* history.c::hs_write() or history_odbc::hs_write_odbc() writes the data into a history file or into an SQL database.
 
 
== History Tag names ==
Tags are only used for MIDAS history events.
 
The mlogger/mhttpd implementation of <span style="color:purple; font-style:italic">/History/Tags</span> has proved troublesome and we are moving away from it.
 
 
;During the transition period:
:  Implementations starting with Version 4435 of [[mlogger]] and [[mhttpd]] (i.e. "new" versions) will now work '''without''' <span style="color:purple; font-style:italic">/History/Tags</span>. The history tags are read directly from the history files themselves. To run in this mode, set  ODB key [[/History ODB tree#DisableTags|/History/DisableTags]] to "y". Existing [[/History ODB tree#Tags subtree|/History/Tags subtree]] will be automatically deleted.
 
Two downsides to running like this are
* it is slower and tags become non-persistent
* if some frontends have not been running for a while, their variables may vanish from the history panel editor.
   
 
=== New-style History Tags ===
For the above two reasons, using <span style="color:purple; font-style:italic">/History/Tags</span> is still recommended. 
However, the format of the tags is now changed to simplify management and reduce ODB size.
 
; For NEW implementations
: the key [[/History ODB tree#CreateOldTags|CreateOldTags]] will not be present. "New-style" history tags will be created automatically in the [[/History ODB tree#Tags subtree|Tags subtree]].
 
 
;If you have old-style tags
: [[mlogger]] will automatically convert the old tags to this new format (this is why you should make a backup of your ODB).
 
** using "old" (i.e. pre Version 4435) mlogger with "new" mhttpd is OK: new mhttpd understands both formats of /History/Tags.
** using "old" mhttpd with "new" mlogger is OK provided the ODB key [[/History ODB tree#CreateOldTags|/History/CreateOldTags]] is set to "y" before starting mlogger.
 
 
 
=== Old-style History Tags ===
Prior to versions 4435 of [[mlogger]] and [[mhttpd]], old-style history tags were generated.
See
* http://ladd00.triumf.ca/~daqweb/doc/midas-old/html/F_History_logging.html
for details.
 
 
 
 
= MIDAS ODBC API access SQL History system =
 
This section describes the internal workings of the MIDAS SQL history system.
 
The SQL history system implements the MIDAS history using a SQL database for data storage instead of flat binary files.
 
The SQL history code lives in a separate files history.h and history_sql.cxx. The present implentation uses the ODBC API for accessing SQL databases.
MySQL is fully supported, Pgsql support is partially implemented, support for arbitrary ODBC drivers should be easy to add in history_sql and most SQL operations are done using an interface class.
 
Preliminary testing with MySQL and PgSQL indicates that disk space requirements are the same for both storage mechanisms using flat binary files or either of the 2 SQL databases. All 3 tested storage mechanisms store the data uncompressed. (Observed gzip-1 compression ratios from CERN-ALPHA history files are 50% or better).
 
Preliminary testing also indicates that MySQL database is "not too slow" for use by T2K/ND280 slow control system. Using MySQL, performance seems to improve somewhat compared to traditional history because each SQL table is stored into a separate file, compared to everything-in-one-file in traditional MIDAS history.
 
== Set up a MySQL database ==
 
In order to setup a MySQL database, the following is needed:
 
*    the server hostname and port number
*    database name
*    user name and password.
 
It is recommended to create 3 different users:
 
*    a "root" user with full priveleges,
*    a "reader" user with read-only priveleges
*    and a "writer" user with "insert, create table, and add column" priveleges (no permission to drop table, remove columns, etc)
 
=== Example ===
#Setup a MySQL database (RHEL/SL 5)
 
ssh root@localhost
service mysqld start
/usr/bin/mysql_secure_installation (enter current password for root: press <enter>, then accept  default answer "Y" to all questions)
mysqladmin -p create history
using mysql-administrator, create 2 users:
history_writer, with database "history" schema privileges: select, insert, create, alter
history_reader, with database "history" schema privileges: select
 
#Setup $HOME/.odbc.ini file:
 
cat $HOME/.odbc.ini
[history_writer]
Description  = history_writer
Driver      = /usr/lib64/libmyodbc3.so
SERVER      = ladd05.triumf.ca
PORT        =
Database    = history
OPTION      = 3
SOCKET      =
User        = history_writer
Password    = ******
[history_reader]
Description  = history_reader
Driver      = /usr/lib64/libmyodbc3.so
SERVER      = ladd05.triumf.ca
PORT        =
Database    = history
OPTION      = 3
SOCKET      =
User        = history_reader
Password    =
 
== Layout of SQL tables ==
 
* One table is created for each history event. Table name is the same as the history event name (as reported by [[mhdump]]).
* one column is created for each history tag (history variable). Column name is the same as the tag name (as reported by mhdump). For array tags, one column is created for each array element: array a[3] will produce columns a_0, a_1 and a_2.
* two special columns are always created: _i_time and _t_time are the timestamps in the UNIX-time integer format and in the SQL "time" format. (A priori, it is not clear which timestamp format is more useful for end users. mhttpd uses the _i_time integer time format). Note that this timestamp is the time when mlogger receives the hot-link signal (see above) and it can be a few seconds behind the time when the user placed the data into the MIDAS bank. For high precision (and sub-second time resolution) time stamps, users should generate their own timestamps and include them as part of the data itself.
* a special table called _history_index is created to remember the mapping between SQL names and MIDAS names for event names, variable name and tag names.
 
=== Schema Evolution ===
 
*    when new data fields are added, new SQL columns are created automatically
*    existing SQL columns are never deleted
*    arrays are expanded automatically, and arrays never shrink.
*    if the type of a data field changes, a conflict may occur with existing SQL columns, for example if previous type was "FLOAT" and new type is "DOUBLE", the existing SQL columns would have the SQL data type "float", too narrow to store new values. mlogger will complain about this. Such conflicts may be resolved by changing the type of the SQL column using SQL tools. In general, SQL names are created from MIDAS names by replacing all non-alphanumerical characters to an underscore "_". If this procedure creates duplicate column names, the column names and made unique by appending them with a random number, i.e. MIDAS names "A+B" and "A-B" will be translated to "A_B" and "A_B_12345" (random integer). True MIDAS names are saved into the _history_index.

Latest revision as of 22:00, 30 October 2026

The midas documentation has moved. The new documentation about the history system is in:

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