1: <HTML>
2: <HEAD>
3: <TITLE>LON-CAPA SQL Database Documentation</TITLE>
4: </HEAD>
5: <BODY>
6: <H1>LON-CAPA SQL Database Documentation</H1>
7: <P>
8: Scott Harrison
9: </P>
10: <P>
11: Last updated: 02/14/2001
12: </P>
13: <P>
14: This file describes issues associated with LON-CAPA
15: and a SQL database.
16: </P>
17: <H2>Latest HOWTO</H2>
18: <P>
19: <UL>
20: <LI>Important notes
21: <LI>Current status of documentation</LI>
22: <LI>Current status of implementation</LI>
23: <LI>Purpose within LON-CAPA</LI>
24: <LI>Dependencies</LI>
25: <LI>Installation</LI>
26: <LI>Installation from source</LI>
27: <LI>Configuration (automated)</LI>
28: <LI>Manual configuration</LI>
29: <LI>Testing</LI>
30: <LI>Example sections of code relevant to LON-CAPA</LI>
31: </UL>
32: </P>
33: <H2>Important notes</H2>
34: <P>
35: It might be worthwhile to look at /usr/local/mysql/manual.html.
36: It is quite in depth.
37: </P>
38: <H2>Current status of documentation</H2>
39: <P>
40: I am going to begin documentation by inserting what notes
41: I have into this file. I will be subsequently rearranging
42: them and editing them based on the tests that I conduct.
43: I am trying to make sure that documentation, installation,
44: and run-time issues are all consistent and correct. The
45: current status of everything is that it works and has
46: been minimally tested, but things need to be cleaned up
47: and checked again!
48: </P>
49: <H2>Current status of implementation</H2>
50: <P>
51: Need to
52: <UL>
53: <LI>Installation: Fix binary file listings for user permissions and ownership.
54: <LI>Installation: Make sure sql server starts, and if database does not
55: exist, then create. (/etc/rc.d).
56: <LI>Processes: Make sure loncron initiates lonsql on library machines.
57: <LI>Read in metadata from right place periodically.
58: <LI>Implement tested perl module handler.
59: </UL>
60: <P>
61: Right now, a lot of "feasibility" work has been done.
62: Recipes for manual installation and configuration have
63: been gathered. Network connectivity of lond->lonsql->lond->lonc
64: type tests have been performed. A binary installation
65: has been compiled in an RPM (LON-CAPA-mysql, with perl components
66: a part of LON-CAPA-systemperl).
67: The most lacking test in terms of feasibility has
68: been looking at benchmarks to analyze the load at which
69: the SQL database can efficiently allow many users to
70: make simultaneous requests of the metadata database.
71: </P>
72: <P>
73: Documentation has been pieced together over time. But,
74: as mentioned in the previous section, it needs an
75: overhaul.
76: </P>
77: <P>
78: The binary installation has some quirks associated with it.
79: Some of the user permissions are wrong, although this is
80: benign. Also, other options of binary installation (such
81: as using binary RPMs put together by others) were dismissed
82: given the difficulty of getting differing combinations of
83: these external RPMs to work together.
84: </P>
85: <P>
86: Most configuration questions have been initially worked out
87: to the point of getting this SQL software component working,
88: however there may be more optimal approaches than currently
89: exist.
90: </P>
91: <H2>Purpose within LON-CAPA</H2>
92: <P>
93: LON-CAPA is meant to distribute A LOT of educational content
94: to A LOT of people. It is ineffective to directly rely on contents
95: within the ext2 filesystem to be speedily scanned for
96: on-the-fly searches of content descriptions. (Simply put,
97: it takes a cumbersome amount of time to open, read, analyze, and
98: close thousands of files.)
99: </P>
100: <P>
101: The solution is to hash-index various data fields that are
102: descriptive of the educational resources on a LON-CAPA server
103: machine. Descriptive data fields are referred to as
104: "metadata". The question then arises as to how this metadata
105: is handled in terms of the rest of the LON-CAPA network
106: without burdening client and daemon processes. I now
107: answer this question in the format of Problem and Solution
108: below.
109: </P>
110: <P>
111: <PRE>
112: PROBLEM SITUATION:
113:
114: If Server A wants data from Server B, Server A uses a lonc process to
115: send a database command to a Server B lond process.
116: lonc= loncapa client process A-lonc= a lonc process on Server A
117: lond= loncapa daemon process
118:
119: database command
120: A-lonc --------TCP/IP----------------> B-lond
121:
122: The problem emerges that A-lonc and B-lond are kept waiting for the
123: MySQL server to "do its stuff", or in other words, perform the conceivably
124: sophisticated, data-intensive, time-sucking database transaction. By tying
125: up a lonc and lond process, this significantly cripples the capabilities
126: of LON-CAPA servers.
127:
128: While commercial databases have a variety of features that ATTEMPT to
129: deal with this, freeware databases are still experimenting and exploring
130: with different schemes with varying degrees of performance stability.
131:
132: THE SOLUTION:
133:
134: A separate daemon process was created that B-lond works with to
135: handle database requests. This daemon process is called "lonsql".
136:
137: So,
138: database command
139: A-lonc ---------TCP/IP-----------------> B-lond =====> B-lonsql
140: <---------------------------------/ |
141: "ok, I'll get back to you..." |
142: |
143: /
144: A-lond <------------------------------- B-lonc <======
145: "Guess what? I have the result!"
146:
147: Of course, depending on success or failure, the messages may vary,
148: but the principle remains the same where a separate pool of children
149: processes (lonsql's) handle the MySQL database manipulations.
150: </PRE>
151: </P>
152: <H2>Dependencies</H2>
153: <P>
154: I believe (but am not 100% confident) that the following
155: RPMs are necessary (in addition to the current ones
156: in rpm_list.txt) to run MySQL. Basically I discovered these
157: dependencies while trying to do external RPM based installs.
158: I assume, and sometimes found, that these dependencies apply
159: to tarball-based distributions too. (So to play it on the
160: safe side, I am going to include these RPMs as part of the
161: core, minimal RPM set.)
162: <UL>
163: <LI>egcs-1.1.2-30</LI>
164: <LI>cpp-1.1.2-30</LI>
165: <LI>glibc-devel-2.1.3-15</LI>
166: <LI>zlib-devel-1.1.3-6</LI>
167: </UL>
168: </P>
169: <H2>Installation</H2>
170: <P>
171: Installation of the LON-CAPA SQL database normally occurs
172: by default when using the LON-CAPA installation CD
173: (see http://install.lon-capa.org). It is installed
174: as the LON-CAPA-mysql RPM. This RPM encodes for the MySQL
175: engine. Related perl interfaces (Perl::DBI, Perl::Msql-Mysql)
176: are encoded in the LON-CAPA-systemperl RPM.
177: </P>
178: <P>
179: The three components of a MySQL installation for the
180: LON-CAPA system are further described immediately below.
181: <TABLE BORDER="0">
182: <TR><TD COLSPAN="2"><STRONG>Perl::DBI module</STRONG>-
183: the API "front-end"...</TD></TR>
184: <TR><TD WIDTH="10%"></TD><TD>database interface module for organizing generic
185: database commands which are independent of specific
186: database implementation (such as MySQL, mSQL, Postgres, etc).
187: </TD></TR>
188: <TR><TD COLSPAN="2"><STRONG>Perl::MySQL module</STRONG>-
189: the API "mid-section"...</TD></TR>
190: <TR><TD WIDTH="10%"></TD><TD>the module to directly interface with the actual
191: MySQL database engine</TD></TR>
192: <TR><TD COLSPAN="2"><STRONG>MySQL database engine</STRONG>-
193: the "back-end"...</TD></TR>
194: <TR><TD WIDTH="10%"></TD><TD>the binary installation (compiled either
195: from source or pre-compiled file listings) which provides the
196: actual MySQL functionality on the system</TD></TR>
197: </TABLE>
198: </P>
199: <H2>Installation from source</H2>
200: <P>
201: Note: the mysql site recommends that Linux users install by
202: using the MySQL RPMs (MySQL-client, MySQL, MySQL-shared, etc).
203: While these RPMs work, I was unsuccessful at integrating
204: this RPM-installed database with perl modules from www.cpan.org.
205: Hence, I <STRONG>strongly</STRONG> recommend that, when installing
206: from "source", MySQL and the perl components be in fact installed
207: from their tarballs (.tar.gz, .tgz). (Perl components, when installed
208: from RPMs, also wound up in incorrect locations on the disk.)
209: Do not coordinate a source install with externally made RPMs!
210: It is, of course, okay to use LON-CAPA RPMs such as LON-CAPA-systemperl
211: and LON-CAPA-mysql since we, in fact, made these RPMs correctly :).
212: <UL>
213: <LI>http://www.cpan.org/authors/id/JWIED/Msql-Mysql-modules-1.2215.tar.gz
214: <BR>This tarball Released 20th August 2000
215: <LI>http://www.mysql.com/Downloads/MySQL-3.23/mysql-3.23.33-pc-linux-gnu-i686.tar.gz
216: <BR>This tarball Last changed 2000-11-11
217: <BR>This is actually a binary tarball (as opposed to source code
218: that is subsequently compiled).
219: <LI>http://www.cpan.org/authors/id/TIMB/DBI-1.14.tar.gz
220: <BR>This tarball Released 14th June 2000
221: </UL>
222: </P>
223: <P>So, here is exactly how I installed MySQL-3.23. (Note that all files
224: wind up in /usr/local/mysql-3.23.33-pc-linux-gnu-i686 except for
225: a link from /usr/local/mysql to /usr/local/mysql-3.23.33-pc-linux-gnu-i686
226: and some files involved in system process handling (/etc/rc.d/*/*mysql).
227: </P>
228: <P>This is how I installed the Msql-Mysql-modules perl modules.
229: <PRE>
230: [root@fenchurch Msql-Mysql-modules-1.2215]# perl Makefile.PL
231: Which drivers do you want to install?
232:
233: 1) MySQL only
234: 2) mSQL only (either of mSQL 1 or mSQL 2)
235: 3) MySQL and mSQL (either of mSQL 1 or mSQL 2)
236:
237: 4) mSQL 1 and mSQL 2
238: 5) MySQL, mSQL 1 and mSQL 2
239:
240: Enter the appropriate number: [3] 1
241:
242:
243: Do you want to install the MysqlPerl emulation? You might keep your old
244: Mysql module (to be distinguished from DBD::mysql!) if you are concerned
245: about compatibility to existing applications! [y] n
246: Where is your MySQL installed? Please tell me the directory that
247: contains the subdir 'include'. [/usr/local/mysql]
248: Which database should I use for testing the MySQL drivers? [test]
249: On which host is database test running (hostname, ip address
250: or host:port) [localhost]
251: [root@fenchurch Msql-Mysql-modules-1.2215]# make
252: [root@fenchurch Msql-Mysql-modules-1.2215]# make test
253: make[1]: Entering directory `/home/user/Msql-Mysql-modules-1.2215/mysql'
254: make[1]: Leaving directory `/home/user/Msql-Mysql-modules-1.2215/mysql'
255: make[1]: Entering directory `/home/user/Msql-Mysql-modules-1.2215/mysql'
256: PERL_DL_NONLAZY=1 /usr/bin/perl -I../blib/arch -I../blib/lib -I/usr/lib/perl5/5.00503/i386-linux -I/usr/lib/perl5/5.00503 -e 'use Test::Harness qw(&runtests $verbose); $verbose=0; runtests @ARGV;' t/*.t
257: t/00base............ok
258: t/10dsnlist.........ok
259: t/20createdrop......ok
260: t/30insertfetch.....ok
261: t/40bindparam.......ok
262: t/40blobs...........ok
263: t/40listfields......ok
264: t/40nulls...........ok
265: t/40numrows.........ok
266: t/50chopblanks......ok
267: t/50commit..........ok
268: t/60leaks...........skipping test on this platform
269: t/ak-dbd............ok
270: t/akmisc............ok
271: t/dbdadmin..........ok
272: t/mysql.............ok
273: t/mysql2............ok
274: All tests successful, 1 test skipped.
275: Files=17, Tests=732, 40 wallclock secs (15.38 cusr + 1.30 csys = 16.68 CPU)
276: [root@fenchurch Msql-Mysql-modules-1.2215]# make install
277:
278: These files are installed.
279: /usr/bin/dbimon
280: /usr/lib/perl5/man/man3/Bundle::DBD::mysql.3
281: /usr/lib/perl5/man/man3/DBD::mysql.3
282: /usr/lib/perl5/man/man3/Mysql.3
283: /usr/lib/perl5/site_perl/5.005/i386-linux/Bundle/DBD/mysql.pm
284: /usr/lib/perl5/site_perl/5.005/i386-linux/DBD/mysql.pm
285: /usr/lib/perl5/site_perl/5.005/i386-linux/Mysql.pm
286: /usr/lib/perl5/site_perl/5.005/i386-linux/Mysql/Statement.pm
287: /usr/lib/perl5/site_perl/5.005/i386-linux/auto/DBD/mysql/mysql.bs
288: /usr/lib/perl5/site_perl/5.005/i386-linux/auto/DBD/mysql/mysql.so
289: /usr/man/man1/dbimon.1
290: /usr/lib/perl5/site_perl/5.005/i386-linux/auto/Msql-Mysql-modules/.packlist
291: </PRE>
292: </P>
293: <P>
294: This is how I installed the DBI perl modules.
295: <PRE>
296: [root@fenchurch DBI-1.14]# perl Makefile.PL
297: *** Note:
298: The optional PlRPC-modules (RPC::PlServer etc) are not installed.
299: If you want to use the DBD::Proxy driver and DBI::ProxyServer
300: modules, then you'll need to install the RPC::PlServer, RPC::PlClient,
301: Storable and Net::Daemon modules. The CPAN Bundle::DBI may help you.
302: You can install them any time after installing the DBI.
303: You do *not* need these modules for typical DBI usage.
304:
305: Optional modules are available from any CPAN mirror, in particular
306: http://www.perl.com/CPAN/modules/by-module
307: http://www.perl.org/CPAN/modules/by-module
308: ftp://ftp.funet.fi/pub/languages/perl/CPAN/modules/by-module
309:
310: Checking if your kit is complete...
311: Looks good
312: Writing Makefile for DBI
313:
314: Remember to actually *read* the README file!
315: Use 'make' to build the software (dmake or nmake on Windows).
316: Then 'make test' to execute self tests.
317: Then 'make install' to install the DBI and then delete this working
318: directory before unpacking and building any DBD::* drivers.
319:
320: [root@fenchurch DBI-1.14]# make
321: [root@fenchurch DBI-1.14]# make test
322: PERL_DL_NONLAZY=1 /usr/bin/perl -Iblib/arch -Iblib/lib -I/usr/lib/perl5/5.00503/i386-linux -I/usr/lib/perl5/5.00503 -e 'use Test::Harness qw(&runtests $verbose); $verbose=0; runtests @ARGV;' t/*.t
323: t/basics............ok
324: t/dbidrv............ok
325: t/examp.............ok
326: t/meta..............ok
327: t/proxy.............skipping test on this platform
328: t/shell.............ok
329: t/subclass..........ok
330: All tests successful, 1 test skipped.
331: Files=7, Tests=179, 7 wallclock secs ( 6.46 cusr + 0.49 csys = 6.95 CPU)
332: PERL_DL_NONLAZY=1 /usr/bin/perl -Iblib/arch -Iblib/lib -I/usr/lib/perl5/5.00503/i386-linux -I/usr/lib/perl5/5.00503 test.pl
333: test.pl
334: DBI test application $Revision: 1.10 $
335: Using /home/user/DBI-1.14/blib
336: Switch: DBI 1.14 by Tim Bunce, 1.14
337: Available Drivers: ADO, ExampleP, Multiplex, Proxy, mysql
338: dbi:ExampleP:: testing 5 sets of 20 connections:
339: Connecting... 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
340: Disconnecting...
341: Connecting... 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
342: Disconnecting...
343: Connecting... 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
344: Disconnecting...
345: Connecting... 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
346: Disconnecting...
347: Connecting... 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
348: Disconnecting...
349: Made 100 connections in 0 wallclock secs ( 0.22 usr + 0.03 sys = 0.25 CPU)
350:
351: Testing handle creation speed...
352: 5000 NullP statement handles cycled in 6.6 cpu+sys seconds (762 per sec)
353:
354: test.pl done
355:
356: [root@fenchurch DBI-1.14]# make install
357: These files are installed.
358: /usr/lib/perl5/site_perl/5.005/i386-linux/auto/DBI/.packlist
359: /usr/bin/dbiproxy
360: /usr/bin/dbish
361: /usr/lib/perl5/man/man3/Bundle::DBI.3
362: /usr/lib/perl5/man/man3/DBD::ADO.3
363: /usr/lib/perl5/man/man3/DBD::Multiplex.3
364: /usr/lib/perl5/man/man3/DBD::Proxy.3
365: /usr/lib/perl5/man/man3/DBI.3
366: /usr/lib/perl5/man/man3/DBI::DBD.3
367: /usr/lib/perl5/man/man3/DBI::FAQ.3
368: /usr/lib/perl5/man/man3/DBI::Format.3
369: /usr/lib/perl5/man/man3/DBI::ProxyServer.3
370: /usr/lib/perl5/man/man3/DBI::Shell.3
371: /usr/lib/perl5/man/man3/DBI::W32ODBC.3
372: /usr/lib/perl5/man/man3/Win32::DBIODBC.3
373: /usr/lib/perl5/site_perl/5.005/i386-linux/Bundle/DBI.pm
374: /usr/lib/perl5/site_perl/5.005/i386-linux/DBD/ADO.pm
375: /usr/lib/perl5/site_perl/5.005/i386-linux/DBD/ExampleP.pm
376: /usr/lib/perl5/site_perl/5.005/i386-linux/DBD/Multiplex.pm
377: /usr/lib/perl5/site_perl/5.005/i386-linux/DBD/NullP.pm
378: /usr/lib/perl5/site_perl/5.005/i386-linux/DBD/Proxy.pm
379: /usr/lib/perl5/site_perl/5.005/i386-linux/DBD/Sponge.pm
380: /usr/lib/perl5/site_perl/5.005/i386-linux/DBI.pm
381: /usr/lib/perl5/site_perl/5.005/i386-linux/DBI/DBD.pm
382: /usr/lib/perl5/site_perl/5.005/i386-linux/DBI/FAQ.pm
383: /usr/lib/perl5/site_perl/5.005/i386-linux/DBI/Format.pm
384: /usr/lib/perl5/site_perl/5.005/i386-linux/DBI/ProxyServer.pm
385: /usr/lib/perl5/site_perl/5.005/i386-linux/DBI/Shell.pm
386: /usr/lib/perl5/site_perl/5.005/i386-linux/DBI/W32ODBC.pm
387: /usr/lib/perl5/site_perl/5.005/i386-linux/Win32/DBIODBC.pm
388: /usr/lib/perl5/site_perl/5.005/i386-linux/auto/DBI/DBI.bs
389: /usr/lib/perl5/site_perl/5.005/i386-linux/auto/DBI/DBI.so
390: /usr/lib/perl5/site_perl/5.005/i386-linux/auto/DBI/DBIXS.h
391: /usr/lib/perl5/site_perl/5.005/i386-linux/auto/DBI/Driver.xst
392: /usr/lib/perl5/site_perl/5.005/i386-linux/auto/DBI/dbd_xsh.h
393: /usr/lib/perl5/site_perl/5.005/i386-linux/auto/DBI/dbi_sql.h
394: /usr/lib/perl5/site_perl/5.005/i386-linux/auto/DBI/dbipport.h
395: /usr/man/man1/dbiproxy.1
396: /usr/man/man1/dbish.1
397: </PRE>
398: </P>
399: <FONT COLOR="green"> old notes in green
400: <P>
401: The following set of tarballs was found to work together
402: properly on a LON-CAPA RedHat 6.2 system:
403: <UL>
404: <LI>DBI-1.13.tar.gz
405: <LI>Msql-Mysql-modules-1.2209.tar.gz
406: <LI>mysql-3.22.32.tar.gz
407: </UL>
408: </P>
409: <P>
410: Installation was simply a matter of following the instructions
411: and typing the several "make" commands for each
412: </P>
413: </FONT>
414: <H2>Configuration (automated)</H2>
415: <P>
416: Not yet developed. This will be part of an interface
417: present on LON-CAPA systems that can be launched by
418: entering the command <TT>/usr/sbin/loncapaconfig</TT>.
419: </P>
420: <H2>Manual configuration</H2>
421: <P>
422: This is not complete.
423: </P>
424: <P>
425: <STRONG>Starting the mysql daemon</STRONG>: Login on the Linux
426: system as user 'www'. Enter the command
427: <TT>/usr/local/bin/safe_mysqld &</TT>
428: </P>
429: <P>
430: <STRONG>Set a password for 'root'</STRONG>:
431: <TT>/usr/local/bin/mysqladmin -u root password 'new-password'</TT>
432: </P>
433: <P>
434: <STRONG>Adding a user</STRONG>: Start the mysql daemon. Login to the
435: mysql system as root (<TT>mysql -u root -p mysql</TT>)
436: and enter the right password (for instance 'newmysql'). Add the user
437: www
438: <PRE>
439: INSERT INTO user (Host, User, Password)
440: VALUES ('localhost','www',password('newmysql'));
441: </PRE>
442: </P>
443: <P>
444: <STRONG>Granting privileges to user 'www'</STRONG>:
445: <PRE>
446: GRANT ALL PRIVILEGES ON *.* TO www@localhost;
447: FLUSH PRIVILEGES;
448: </PRE>
449: </P>
450: <P>
451: <STRONG>Set the SQL server to start upon system startup</STRONG>:
452: Copy support-files/mysql.server to the right place on the system
453: (/etc/rc.d/...).
454: </P>
455: <P>
456: <STRONG>The Perl API</STRONG>
457: <PRE>
458: $dbh = DBI->connect( "DBI:mysql:loncapa",
459: "www",
460: "SOMEPASSWORD",
461: { RaiseError =>0,PrintError=>0});
462:
463: There is an obvious need to CONNECT to the database, and in order to do
464: this, there must be:
465: a RUNNING mysql daemon;
466: a DATABASE named "loncapa";
467: a USER named "www";
468: and an ABILITY for LON-CAPA on one machine to access
469: SQL database on another machine;
470:
471: So, here are some notes on implementing these configurations.
472:
473: ** RUNNING mysql daemon (safe_mysqld method)
474:
475: The recommended way to run the MySQL daemon is as a non-root user
476: (probably www)...
477:
478: so, 1) login as user www on the linux machine
479: 2) start the mysql daemon as /usr/local/bin/safe_mysqld &
480:
481: safe_mysqld only works if the local installation of MySQL is set to the
482: right directory permissions which I found to be:
483: chown www:users /usr/local/var/mysql
484: chown www:users /usr/local/lib/mysql
485: chown -R www:users /usr/local/mysql
486: chown www:users /usr/local/include/mysql
487: chown www:users /usr/local/var
488:
489: ** DATABASE named "loncapa"
490:
491: As user www, run this command
492: mysql -u root -p mysql
493: enter the password as SOMEPASSWORD
494:
495: This allows you to manually enter MySQL commands.
496: The MySQL command to generate the loncapa DATABASE is:
497:
498: CREATE DATABASE 'loncapa';
499:
500: ** USER named "www"
501:
502: As user www, run this command
503: mysql -u root -p mysql
504: enter the password as SOMEPASSWORD
505:
506: To add the user www to the MySQL server, and grant all
507: privileges on *.* to www@localhost identified by 'SOMEPASSWORD'
508: with grant option;
509:
510: INSERT INTO user (Host, User, Password)
511: VALUES ('localhost','www',password('SOMEPASSWORD'));
512:
513: GRANT ALL PRIVILEGES ON *.* TO www@localhost;
514:
515: FLUSH PRIVILEGES;
516:
517: ** ABILITY for LON-CAPA machines to communicate with SQL databases on
518: other LON-CAPA machines
519:
520: An up-to-date lond and lonsql.
521: </PRE>
522: </P>
523: <H2>Testing</H2>
524: <P>
525: <PRE>
526: <STRONG>** TEST the database connection with my current tester.pl code
527: which mimics what command will eventually be sent through lonc.</STRONG>
528:
529: $reply=reply(
530: "querysend:SELECT * FROM general_information WHERE Id='AAAAA'",$lonID);
531: </PRE>
532: </P>
533: <H2>Example sections of code relevant to LON-CAPA</H2>
534: <P>
535: Here are excerpts of code which implement the above handling:
536: </P>
537: <P>
538: <PRE>
539: <STRONG>**LONSQL
540: A subroutine from "lonsql" which establishes a child process for handling
541: database interactions.</STRONG>
542:
543: sub make_new_child {
544: my $pid;
545: my $sigset;
546:
547: # block signal for fork
548: $sigset = POSIX::SigSet->new(SIGINT);
549: sigprocmask(SIG_BLOCK, $sigset)
550: or die "Can't block SIGINT for fork: $!\n";
551:
552: die "fork: $!" unless defined ($pid = fork);
553:
554: if ($pid) {
555: # Parent records the child's birth and returns.
556: sigprocmask(SIG_UNBLOCK, $sigset)
557: or die "Can't unblock SIGINT for fork: $!\n";
558: $children{$pid} = 1;
559: $children++;
560: return;
561: } else {
562: # Child can *not* return from this subroutine.
563: $SIG{INT} = 'DEFAULT'; # make SIGINT kill us as it did before
564:
565: # unblock signals
566: sigprocmask(SIG_UNBLOCK, $sigset)
567: or die "Can't unblock SIGINT for fork: $!\n";
568:
569:
570: #open database handle
571: # making dbh global to avoid garbage collector
572: unless (
573: $dbh = DBI->connect("DBI:mysql:loncapa","www","SOMEPASSWORD",{ RaiseError =>0,PrintError=>0})
574: ) {
575: my $st=120+int(rand(240));
576: &logthis("<font color=blue>WARNING: Couldn't connect to database ($st secs): $@</font>");
577: print "database handle error\n";
578: sleep($st);
579: exit;
580:
581: };
582: # make sure that a database disconnection occurs with ending kill signals
583: $SIG{TERM}=$SIG{INT}=$SIG{QUIT}=$SIG{__DIE__}=\&DISCONNECT;
584:
585: # handle connections until we've reached $MAX_CLIENTS_PER_CHILD
586: for ($i=0; $i < $MAX_CLIENTS_PER_CHILD; $i++) {
587: $client = $server->accept() or last;
588:
589: # do something with the connection
590: $run = $run+1;
591: my $userinput = <$client>;
592: chomp($userinput);
593:
594: my ($conserver,$querytmp)=split(/&/,$userinput);
595: my $query=unescape($querytmp);
596:
597: #send query id which is pid_unixdatetime_runningcounter
598: $queryid = $thisserver;
599: $queryid .="_".($$)."_";
600: $queryid .= time."_";
601: $queryid .= $run;
602: print $client "$queryid\n";
603:
604: #prepare and execute the query
605: my $sth = $dbh->prepare($query);
606: my $result;
607: unless ($sth->execute())
608: {
609: &logthis("<font color=blue>WARNING: Could not retrieve from database: $@</font>");
610: $result="";
611: }
612: else {
613: my $r1=$sth->fetchall_arrayref;
614: my @r2; map {my $a=$_; my @b=map {escape($_)} @$a; push @r2,join(",", @b)} (@$r1);
615: $result=join("&",@r2) . "\n";
616: }
617: &reply("queryreply:$queryid:$result",$conserver);
618:
619: }
620:
621: # tidy up gracefully and finish
622:
623: #close the database handle
624: $dbh->disconnect
625: or &logthis("<font color=blue>WARNING: Couldn't disconnect from database $DBI::errstr ($st secs): $@</font>");
626:
627: # this exit is VERY important, otherwise the child will become
628: # a producer of more and more children, forking yourself into
629: # process death.
630: exit;
631: }
632: }
633: </P>
634: <P>
635: <STRONG>** LOND enabling of MySQL requests</STRONG>
636: <BR />
637: This code is part of every lond child process in the
638: way that it parses command request syntax sent to it
639: from lonc processes. Based on the diagram above, querysend
640: corresponds to B-lonc sending the result of the query.
641: queryreply corresponds to B-lond indicating that it has
642: received the request and will start the database transaction
643: (it returns "ok" to
644: A-lonc ($client)).
645: <PRE>
646: # ------------------------------------------------------------------- querysend
647: } elsif ($userinput =~ /^querysend/) {
648: my ($cmd,$query)=split(/:/,$userinput);
649: $query=~s/\n*$//g;
650: print $client sqlreply("$hostid{$clientip}\&$query")."\n";
651: # ------------------------------------------------------------------ queryreply
652: } elsif ($userinput =~ /^queryreply/) {
653: my ($cmd,$id,$reply)=split(/:/,$userinput);
654: my $store;
655: my $execdir=$perlvar{'lonDaemons'};
656: if ($store=IO::File->new(">$execdir/tmp/$id")) {
657: print $store $reply;
658: close $store;
659: print $client "ok\n";
660: }
661: else {
662: print $client "error:$!\n";
663: }
664:
665: </PRE>
666:
667: </P>
668: </BODY>
669: </HTML>
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