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Debugging InstantDB Applications

It can sometimes be useful to be able to see what's going on inside InstantDB. This can be particularly useful when problems occur during recovery or when deadlocks occur.

The SET EXPORT is mainly used to export results sets to text files. However it can also be used to set the level of diagnostic tracing which is enabled. The syntax when used in this way is:

SET EXPORT <log file> TRACE <level>
   [CONSOLE] [TIME]

Trace levels are organized as a bitmap. Setting the appropriate bit causes the associated level of tracing to be activated. The various bits are defined via the following public final ints in the db.Trace class:

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Constant	Value	Bit	Description
TR_EVENT	1	0	Major events such as database open and close
TR_SQL	2	1	Logs each SQL statment processed
TR_ERROR	4	2	Logs errors
TR_OPEN	8	3	Table open and close
TR_TRANS	16	4	Transaction processing and locking
TR_PROGRESS	32	5	Progress of imports and index builds
TR_CACHE	64	6	Cache activity
TR_MEM	128	7	Memory and garbage collection
TR_INDEX	256	8	Index activity
TR_PARSE	512	9	SQL parsing
TR_JDBC	1024	10	JDBC calls
TR_EXPORT	2048	11	Used internally by SET EXPORT
TR_TABLESCAN	4096	12	Table scans during SELECTs

SET EXPORT "fred.log" TRACE 18

would set tracing on for SQL processing and transaction processing. Note that, unlike dumping results sets, trace levels are set globally. So if any one thread sets a trace bit on, all other threads are affected. This inconsistency in the SET EXPORT command is unfortunate, but it has turned out to be necessary for performance reasons.

Including the optional CONSOLE keyword causes tracing to also be directed to standard out. The TIME keyword causes the GMT time to be output along with every trace line.

The properties traceLevel, traceFile and traceConsole determine the initial tracing which is produced (i.e. before a thread executes the SET EXPORT command).