|Persisting Table Data to GemFire XD Disk Stores / Disk Store Management|
You can configure automatic compaction for an operation log based on percentage of garbage content. You can also request compaction manually for online and offline disk stores.
When a DML operation is added to a disk store, any preexisting operation record for the same record becomes obsolete, and GemFire XD marks it as garbage. For example, when you update a record, the update operation is added to the store. If you delete the record later, the delete operation is added and the update operation becomes garbage. GemFire XD does not remove garbage records as it goes, but it tracks the percentage of garbage in each operation log, and provides mechanisms for removing garbage to compact your log files.
GemFire XD compacts an old operation log by copying all non-garbage records into the current log and discarding the old files. As with logging, oplogs are rolled as needed during compaction to stay within the MAXLOGSIZE setting.
You can configure the system to automatically compact any closed operation log when its garbage content reaches a certain percentage. You can also manually request compaction for online and offline disk stores. For the online disk store, the current operation log is not available for compaction, no matter how much garbage it contains.
Offline compaction runs essentially in the same way, but without the incoming DML operations. Also, because there is no current open log, the compaction creates a new one to get started.
Offline compaction is a manual process. All log files are compacted as much as possible, regardless of how much garbage they hold. Offline compaction creates new log files for the compacted log records.
gfxd compact-disk-store myDiskStoreName /firstDir /secondDir -maxOplogSize=maxMegabytesForOplog
You must provide all of the directories in the disk store. If no oplog max size is specified, GemFire XD uses the system default.
Offline compaction can take a lot of memory. If you get a java.lang.OutOfMemory error while running this, you made need to increase your heap size. See the gfxd command help for instructions on how to do this.
You can improve performance during busy times if you disable automatic compaction and run your own manual compaction during lighter system load or during downtimes. You could run the API call after your application performs a large set of data operations. You could run gfxd compact-all-disk-stores every night when system use is very low.
To follow a strategy like this, you need to set aside enough disk space to accommodate all non-compacted disk data. You might need to increase system monitoring to make sure you do not overrun your disk space. You may be able to run only offline compaction. If so, you can set ALLOWFORCECOMPACTION to false and avoid storing the information required for manual online compaction.
bash-2.05$ ls -ltra backupDirectory total 28 -rw-rw-r-- 1 jpearson users 3 Apr 7 14:56 BACKUPds1_3.drf -rw-rw-r-- 1 jpearson users 25 Apr 7 14:56 BACKUPds1_3.crf drwxrwxr-x 3 jpearson users 1024 Apr 7 15:02 .. -rw-rw-r-- 1 jpearson users 7085 Apr 7 15:06 BACKUPds1.if -rw-rw-r-- 1 jpearson users 18 Apr 7 15:07 BACKUPds1_4.drf -rw-rw-r-- 1 jpearson users 1070 Apr 7 15:07 BACKUPds1_4.crf drwxrwxr-x 2 jpearson users 512 Apr 7 15:07 . bash-2.05$ gfxd validate-disk-store ds1 backupDirectory /root: entryCount=6 /partitioned_region entryCount=1 bucketCount=10 Disk store contains 12 compactable records. Total number of region entries in this disk store is: 7 bash-2.05$ gfxd compact-disk-store ds1 backupDirectory Offline compaction removed 12 records. Total number of region entries in this disk store is: 7 bash-2.05$ ls -ltra backupDirectory total 16 -rw-rw-r-- 1 jpearson users 3 Apr 7 14:56 BACKUPds1_3.drf -rw-rw-r-- 1 jpearson users 25 Apr 7 14:56 BACKUPds1_3.crf drwxrwxr-x 3 jpearson users 1024 Apr 7 15:02 .. -rw-rw-r-- 1 jpearson users 0 Apr 7 15:08 BACKUPds1_5.drf -rw-rw-r-- 1 jpearson users 638 Apr 7 15:08 BACKUPds1_5.crf -rw-rw-r-- 1 jpearson users 2788 Apr 7 15:08 BACKUPds1.if drwxrwxr-x 2 jpearson users 512 Apr 7 15:09 . bash-2.05$