For example, your application, when it is started, can determine if a deletion is in progress. Because journal deletions persist across system restarts, services and applications started at system restart should check for an ongoing deletion.
Change journals are not necessarily created at startup. To create a change journal, an administrator may do so explicitly or start another service that requires a change journal. Skip to main content. This browser is no longer supported.
The hash field is a hash value of the payload. Field objects are used to enumerate all possible values a certain field name can take in the entire journal file. This value is usable to check the contents of the entry, being independent of the order of the DATA objects in the array. The items[] array contains references to all DATA objects of this entry, plus their respective hashes. For continuous parts of the file written during the same boot i.
Modulo wallclock time jumps due to incorrect clocks being corrected the realtime timestamps are monotonic too. Empty cells have both offsets set to 0. These offsets do not point to the object headers but directly to the payloads.
When a new journal file is created the two hash table objects need to be created right away as first two objects in the stream. Entry Arrays are used to store a sorted array of offsets to entries. Entry arrays are strictly sorted by offsets on disk, and hence by their timestamps and sequence numbers with some restrictions, see above. Entry Arrays are chained up.
To optimize allocation and seeking, as entry arrays are appended to a chain of entry arrays they should increase in size double. Due to being monotonically ordered entry arrays may be searched with a binary search bisection. One chain of entry arrays links up all entries written to the journal. Tag objects are used to seal off the journal for alteration. In regular intervals a tag object is appended to the file. The tag object consists of a SHA HMAC tag that is calculated from the objects stored in the file since the last tag was written, or from the beginning if no tag was written yet.
The sequence number seqnum is increased with each tag. When calculating the HMAC of objects header fields that are volatile are excluded skipped.
More specifically all fields that might validly be altered to maintain a consistent file structure such as offsets to objects added later for the purpose of linked lists and suchlike after an object has been written are not protected by the tag. This means a verifier has to independently check these fields for consistency of structure. For the fields excluded from the HMAC please consult the source code directly.
A verifier should read the file from the beginning to the end, always calculating the HMAC for the objects it reads. Each time a tag object is encountered the HMAC should be verified and restarted.
The tag object sequence numbers need to increase strictly monotonically. Tag objects themselves are partially protected by the HMAC i. Given an offset to an entry all data fields are easily found by following the offsets in the data item array of the entry. When seeking or listing with one field match applied the DATA object of the match is first identified, and then its data entry array chain traversed.
If multiple matches are applied, multiple chains of entry arrays should be traversed in parallel. Since they all are strictly monotonically ordered by offset of the entries, advancing in one can be directly applied to the others, until an entry matching all matches is found. In the worst case seeking like this is O n where n is the number of matching entries of the "loosest" match, but in the common case should be much more efficient at least for the well-known fields, where the set of possible field values tend to be closely related.
When interleaving multiple journal files seeking tends to be a frequently used operation, but in this case can be effectively suppressed by caching results from previous entries. This browser is no longer supported.
Download Microsoft Edge More info. Contents Exit focus mode. Please rate your experience Yes No. Any additional feedback? Important Beginning with Windows 10, version , journal. In this article. Warning: This site requires the use of scripts, which your browser does not currently allow. See how to enable scripts. Windows Journal Application for Windows for xbased Systems. Select Language:.
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