CreateTransaction: suggest/enforce fee for big low-priority transactions to avoid backlog #86

1. 
   molecular commented at 2:54 am on March 1, 2011: none

   currently (2011/03/01) a backlog of transactions that dont seem make it into blocks is building up (according to ArtForz now 670 transactions).

   People are starting to complain, see http://www.bitcoin.org/smf/index.php?topic=3835.msg57031#msg57031 for an example.

   This was discussed on #bitcoin-dev

   ArtForz> that tx should have a score of 20567855 ArtForz> so it falls short of the dPriority > COIN * 144 / 250 test ArtForz> and as tx size is > 4000, fAllowFree is never true for it theymos> Ah. So it will never confirm? ArtForz> probably not

   ArtForz> looks like the tx-sending code needs some fixing molecular> like not generate a tx with a score too low, or suggest to add a fee? ArtForz> yep ArtForz> check size and priority of transaction, if it’s > 4kB and score < 57600000 require min fee ArtForz> maybe reduce the size limit to 3.5k or so, otherwise it can only get into an otherwise empty block

   This also seems to imply the possiblity of a DoS-Attack on node RAM, since the tx-queue is kept im RAM. Maybe the transaction cache should not be unlimited?

2. 
   gasteve commented at 3:11 am on March 1, 2011: none

   Is there another potential issue here? For transactions that, for one reason or another, don’t get into a block in a reasonable amount of time, is there some criteria for which the network will drop (and thereby cancel) such transactions? (like a certain amount of time passing without being included in a block)
3. 
   molecular commented at 2:16 pm on March 1, 2011: none

   afaik, there is currently no mechanism that would drop transactions from local cache. They just stay there until found in a block.

   It’s been suggested to do that, though (like limit local cache to 5MB), in order to avoid DoS attack. It’s probably not that simple, though.

   Don’t know if there’s a github issue for this, if not, it certainly deserves one.

4. 
   gavinandresen commented at 3:40 pm on March 1, 2011: contributor

   Lets discuss on the forum: http://www.bitcoin.org/smf/index.php?topic=4009.msg57469
5. 
   jgarzik commented at 3:17 am on March 3, 2011: contributor

   See pull request at #88
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Contributors
molecular gasteve gavinandresen jgarzik

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