Evo Scan Download

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Raguel Charrette

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Aug 3, 2024, 4:17:59 PM8/3/24

to contchlorlesspatch

On the Android app (version 266.2.2) I scanned a document but I received an error message while trying to upload it, both on data and on wi-fi. I assumed that I would be able to access the saved file on my device (in JPG format) after I closed the error screen, however the file doesn't seem to exist.

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Thanks for your reply. I can't remember exactly but it was something along the lines of 'waiting for internet connection'. (This was despite me being online). I assumed it was a glitch in the network and that the original file would be available when I went back a step - I had already saved the file as a JPG, hence my looking for it somewhere on my device.

Do not use the dropbox scanner if you want the upload of your files to be guaranteed; if the mobile app cannot upload your files to Dropbox.com AT THE MOMENT it is scanned, the app permanently and immediately deletes your scanned document and tells you "File to Upload Not Found."

I recommend using a local scanner application instead and and manually upload the scanned file.

For the Developers...
Dropbox needs to hold scanned files in some temporary buffer and not give up entirely if it cannot immediately upload the scanned file - in fact, that file should not be deleted at all until Dropbox.com sends positive confirmation that "Yes, you uploaded VERY_IMPORTANT_SCAN.pdf. Yes, I received it. Yes, I have it. Yes, you can delete the copy in your local buffer."

Yes, that is feedback for the developers. No, I do not think it will actually make it to the dev room - please forgive my cynicism.

I scanned a receipt yesterday and didn't have internet at the time. Today I saw a top of screen notification that the upload failed, not a problem I thought I just retry, but there is no way to do it in the app, and the notification is gone, so unfortunately I cannot tell you the exact message in it. I am very confused by this discussion. Is there really no way to retry an upload?

Since these commands allow for incremental iteration, returning only a small number of elements per call, they can be used in production without the downside of commands like KEYS or SMEMBERS that may block the server for a long time (even several seconds) when called against big collections of keys or elements.

However while blocking commands like SMEMBERS are able to provide all the elements that are part of a Set in a given moment, The SCAN family of commands only offer limited guarantees about the returned elements since the collection that we incrementally iterate can change during the iteration process.

Note that SCAN, SSCAN, HSCAN and ZSCAN all work very similarly, so this documentation covers all four commands. However an obvious difference is that in the case of SSCAN, HSCAN and ZSCAN the first argument is the name of the key holding the Set, Hash or Sorted Set value. The SCAN command does not need any key name argument as it iterates keys in the current database, so the iterated object is the database itself.

Since in the second call the returned cursor is 0, the server signaled to the caller that the iteration finished, and the collection was completely explored. Starting an iteration with a cursor value of 0, and calling SCAN until the returned cursor is 0 again is called a full iteration.

SCAN, SSCAN, HSCAN and ZSCAN return a two element multi-bulk reply, where the first element is a string representing an unsigned 64 bit number (the cursor), and the second element is a multi-bulk with an array of elements.

SCAN family functions do not guarantee that the number of elements returned per call are in a given range. The commands are also allowed to return zero elements, and the client should not consider the iteration complete as long as the returned cursor is not zero.

However the number of returned elements is reasonable, that is, in practical terms SCAN may return a maximum number of elements in the order of a few tens of elements when iterating a large collection, or may return all the elements of the collection in a single call when the iterated collection is small enough to be internally represented as an encoded data structure (this happens for small Sets, Hashes and Sorted Sets).

While SCAN does not provide guarantees about the number of elements returned at every iteration, it is possible to empirically adjust the behavior of SCAN using the COUNT option. Basically with COUNT the user specifies the amount of work that should be done at every call in order to retrieve elements from the collection. This is just a hint for the implementation, however generally speaking this is what you could expect most of the times from the implementation.

Important: there is no need to use the same COUNT value for every iteration. The caller is free to change the count from one iteration to the other as required, as long as the cursor passed in the next call is the one obtained in the previous call to the command.

It is important to note that the MATCH filter is applied after elements are retrieved from the collection, just before returning data to the client. This means that if the pattern matches very little elements inside the collection, SCAN will likely return no elements in most iterations. An example is shown below:

When using Redis Cluster, the search is optimized for patterns that imply a single slot.If a pattern can only match keys of one slot,Redis only iterates over keys in that slot, rather than the whole database,when searching for keys matching the pattern.For example, with the pattern ah*llo, Redis would only try to match it with the keys in slot 15495, which hash tag a implies.To use pattern with hash tag, see Hash tags in the Cluster specification for more information.

You can use the TYPE option to ask SCAN to only return objects that match a given type, allowing you to iterate through the database looking for keys of a specific type. The TYPE option is only available on the whole-database SCAN, not HSCAN or ZSCAN etc.

The type argument is the same string name that the TYPE command returns. Note a quirk where some Redis types, such as GeoHashes, HyperLogLogs, Bitmaps, and Bitfields, may internally be implemented using other Redis types, such as a string or zset, so can't be distinguished from other keys of that same type by SCAN. For example, a ZSET and GEOHASH:

It is important to note that the TYPE filter is also applied after elements are retrieved from the database, so the option does not reduce the amount of work the server has to do to complete a full iteration, and for rare types you may receive no elements in many iterations.

It is possible for an infinite number of clients to iterate the same collection at the same time, as the full state of the iterator is in the cursor, that is obtained and returned to the client at every call. No server side state is taken at all.

Since there is no state server side, but the full state is captured by the cursor, the caller is free to terminate an iteration half-way without signaling this to the server in any way. An infinite number of iterations can be started and never terminated without any issue.

Calling SCAN with a broken, negative, out of range, or otherwise invalid cursor, will result in undefined behavior but never in a crash. What will be undefined is that the guarantees about the returned elements can no longer be ensured by the SCAN implementation.

The SCAN algorithm is guaranteed to terminate only if the size of the iterated collection remains bounded to a given maximum size, otherwise iterating a collection that always grows may result into SCAN to never terminate a full iteration.

This is easy to see intuitively: if the collection grows there is more and more work to do in order to visit all the possible elements, and the ability to terminate the iteration depends on the number of calls to SCAN and its COUNT option value compared with the rate at which the collection grows.

In the COUNT option documentation, we state that sometimes this family of commands may return all the elements of a Set, Hash or Sorted Set at once in a single call, regardless of the COUNT option value. The reason why this happens is that the cursor-based iterator can be implemented, and is useful, only when the aggregate data type that we are scanning is represented as a hash table. However Redis uses a memory optimization where small aggregate data types, until they reach a given amount of items or a given max size of single elements, are represented using a compact single-allocation packed encoding. When this is the case, SCAN has no meaningful cursor to return, and must iterate the whole data structure at once, so the only sane behavior it has is to return everything in a call.