Question Re: How do I simulate assertions with SQL Anywhere 16? in Technology Q&A

How do I simulate assertions with SQL Anywhere 16?

Breck_Carter — Thu, 14 Mar 2013 09:29:14 GMT

I want test the behavior of various dbsrv16 -ufd option settings when server-level and database-level assertions occur.

I don't care what the assertion codes are, so fakes are OK.

Re: How do I simulate assertions with SQL Anywhere 16?

VolkerBarth — Thu, 14 Mar 2013 10:00:18 GMT

Agreed, it would be handy if one could "fake an assertion" just as one might want to fake a "database validation error" when testing a backup/validation plan - IIRC, the latter has been asked in the past...

Re: How do I simulate assertions with SQL Anywhere 16?

MarkCulp — Thu, 14 Mar 2013 10:01:11 GMT

One way to generate assertions would be to create a database and then corrupt it by changing the checksum on one of the database pages.

WARNING: DO NOT DO THIS ON ANY DATABASE WITH REAL DATA !!

dbinit bad.db
perl corrupt_the_database.pl bad.db

where corrupt_the_database.pl is the perl script containing:

#
# Corrupt the checksum on page 3 of a SQL Anywhere database
# !! USE WITH EXTREME CARE !!
#
chmod( 0777, $ARGV[0] );
open( FOO, "+<$ARGV[0]" ) || die $?;
binmode( FOO );
seek( FOO, 3*4096-4, 0 ) || die $?;
print( FOO '\\0\\0\\0\\0' ) || die $?;
seek( FOO, 0, 2 );
close( FOO );

When you start the database on bad.db (e.g. "dbeng16 bad.db") the server will generate a "Checksum failure" assertion.

Re: How do I simulate assertions with SQL Anywhere 16?

Breck_Carter — Thu, 14 Mar 2013 10:09:20 GMT

Presumably, that is a permanent error condition. Is there any way to cause a transient assertion, one that would allow dbsrv16 -ufd restart to successfully restart the database?

Re: How do I simulate assertions with SQL Anywhere 16?

MarkCulp — Thu, 14 Mar 2013 10:30:05 GMT

Yes, the corrupted checksum failure would be a permanent condition and therefore the restart attempt would fail.

I do not know of any publicly available way of causing a temporary assertion.

Perhaps one way would be to create a user table, put some data in it, add an index, shutdown the database, and then corrupt the index using a method similar to the above process. Starting the database on such a table would succeed but accessing the table may cause an assertion if the corruption was "just right". Again this type of corruption would be permanent but the restart of the database would succeed.

Re: How do I simulate assertions with SQL Anywhere 16?

VolkerBarth — Thu, 14 Mar 2013 10:47:47 GMT

Well, the typical EBF readme does contain several bug fixes for (temporary) assertions - some of them are declared with "under very rare circumstances" and the like, others sound reproducable.

Is that a starting point?

Yes, I know, v16 is brandnew, so there are no EBFs and readmes available yet...

Re: How do I simulate assertions with SQL Anywhere 16?

VolkerBarth — Thu, 14 Mar 2013 10:48:51 GMT

@Breck: Are you working on "The top 10 cool features of SQL Anywhere 16"? (In case that allows for a publicly available answer:))

Re: How do I simulate assertions with SQL Anywhere 16?

Breck_Carter — Thu, 14 Mar 2013 10:54:49 GMT

Soooo... a valuable new feature exists with no way to prove it... 🙂

Re: How do I simulate assertions with SQL Anywhere 16?

Breck_Carter — Thu, 14 Mar 2013 10:55:24 GMT

@Volker: What a great idea, someone should write that!

Re: How do I simulate assertions with SQL Anywhere 16?

MarkCulp — Thu, 14 Mar 2013 11:19:17 GMT

Well, we've proved it in house... but I'm working on a method for you to prove it to yourself... give me a few more ~~minutes~~ days.

Re: How do I simulate assertions with SQL Anywhere 16?

Breck_Carter — Thu, 14 Mar 2013 18:02:49 GMT

Take all the time you need, take weeks!

Re: How do I simulate assertions with SQL Anywhere 16?

VolkerBarth — Mon, 08 Apr 2013 05:52:40 GMT

Well, someone seems to have just done that:

Top 10 Cool New Features in SAP Sybase SQL Anywhere 16...

Isn't that a smart "nearly-invisible announcement":)