Hey John, I just tested r510 and i'm please to say that not only it passes all my test cases (with -DFASTBIT_EMPTY_STRING_AS_NULL), but it is also unbelievably faster (more than 25% in my test) ! I'm not sure exactly why but this is greatly appreciated. Could it be the move from the simple loop in category::patternSearch to the much more sophisticated index::sumBins ?
Do you have a lot of thing to change before the stable release ? I admit that i'd prefer use a stable release too rather than r506. Thanks, -----Original Message----- From: K. John Wu [mailto:[email protected]] Sent: Saturday, March 31, 2012 1:33 AM To: Dominique Prunier Cc: FastBit Users Subject: Re: [FastBit-users] PATCH: perf boost on top of r501 Hi, Dominique, I have added a couple of more test cases involving special characters in the test suite used by 'make check'. The latest SVN revision is 510. Things seem to work OK. I would like to wrap things for a stable research soon. If you find anything that needs attention please let me know. John On 3/29/12 1:23 PM, Dominique Prunier wrote: > Hey John, > > I found the problem. When the exact value doesn't exists in the dictionary, > operator[] is supposed to return size()+1 but here it returns 3 instead of 2 > (it returns raw_.size()+1 instead of key_.size()+1) which make the following > code fail in dictionary::patternSearch: > > if (!meta) { > uint32_t code = operator[](prefix.c_str()); > if (code != size() + 1) { > matches.push_back(code); > } > return; > } > > We probably never saw it before for at least 3 reasons: > * it only affects linear search from dictionary::operator[] since in the > other case it returns raw_.size() so it can't happen is the dic is larger > than 16 > * index::getBitvector that was previously used in category::patternSearch > validate the given index and return 0 if it is out of bounds > * category::patternSearch was validating that index::getBitvector didn't > return NULL > > Thanks, > > -----Original Message----- > From: K. John Wu [mailto:[email protected]] > Sent: Thursday, March 29, 2012 3:48 PM > To: Dominique Prunier > Cc: FastBit Users > Subject: Re: [FastBit-users] PATCH: perf boost on top of r501 > > Hi, Dominique, > > The query seg faulted in r507 because ibis::dictionary::patternSearch > placed the number 3 into the output array, however, the dictionary has > only one value "\"val%\"". This creates an opportunity for > ibis::index::sumBins attempt to access bits[3], but there are only two > values in bits. Any idea why is ibis::dictionary::patternSearch > producing 3? > > John > > > On 3/29/12 10:05 AM, Dominique Prunier wrote: >> Hey John, >> >> I'm sorry, my test case was not really "minimal" and too complex for what i >> wanted to show you. >> Please don't change the escaping, the query evaluation works just fine. >> >> Just for your information, this test case was here to validate one thing: >> consistent de-escaping in all layers: >> - C source : "'\"val\\\\%'" >> - Compiled : '"val\\%' >> - After lexer : "val\\% >> - In qLike : "val\% >> Ultimately, this tests try to validate that % escaping works in patternMatch >> by not treating % as a wildcard but as a regular character, thus this is not >> supposed to return any match (it ends up being an equivalent of = "val%). >> And it works just as expected. There is nothing to change about it. >> >> However, it just happened to be a query that used to segfault in r507, but >> my guess is that it was related to one of these specificities: >> * this column only has a single value >> * there is no nulls >> * the query returns no results >> >> To give you a simpler example, the query: >> >> SELECT single_value_category FROM <partition> WHERE single_value_category >> LIKE 'missing' >> >> segfaulted as well in r507 for the same reasons. And this exemple doesn't >> involve any fancy de-escaping but share the same specificities (single >> value, no nulls, no results). >> >> Thanks, >> >> -----Original Message----- >> From: K. John Wu [mailto:[email protected]] >> Sent: Thursday, March 29, 2012 12:41 PM >> To: Dominique Prunier >> Cc: FastBit Users >> Subject: Re: [FastBit-users] PATCH: perf boost on top of r501 >> >> Hi, Dominique, >> >> I see what you are trying to do. The weird_category only has value >> "\"val%\"", therefore, the where clause "weird_category LIKE >> '\"val\\%'" should match every row, but "weird_category LIKE 'val\\%'" >> should match no row. >> >> If you can step into category::patternSearch, you will see that >> "val\\%" has been stripped to "val%", which will have the same outcome >> as you intended, but it stripped away too many back slashes. You >> intend category::patternSearch to see "val\%" to match the literal >> percent sign (%), however, because the back slash was stripped twice, >> you only got a bare percent sign left, which means it is a wild card >> character, not a literal character as you intended. >> >> My theory is this. The string "val\\%" becomes "val\%" when it gets >> to inside the C code. The runtime system has stripped away the first >> back slash. The constructor of ibis::qLike take away the second one. >> >> Since we have gone back and forth many times on this, I will wait for >> you confirmation before doing anything about it. >> >> John >> >> >> On 3/29/12 8:09 AM, Dominique Prunier wrote: >>> Hey John, >>> >>> When i'll have some time, i'll make my test suite dump the queries and >>> expected results so that you try it yourself. It only tests category (and a >>> small bit of long) data types for the things i'm doing but it can be useful. >>> >>> In the meantime, here is my test partition (see attached) and the query >>> that generated the segfault with r507 was: >>> >>> SELECT weird_category FROM <partition> WHERE weird_category LIKE '"val\\%' >>> (which is not supposed to return any result) >>> >>> It might help you understand what could have happened. >>> >>> Thanks, >>> >>> -----Original Message----- >>> From: K. John Wu [mailto:[email protected]] >>> Sent: Thursday, March 29, 2012 10:55 AM >>> To: Dominique Prunier >>> Cc: FastBit Users >>> Subject: Re: [FastBit-users] PATCH: perf boost on top of r501 >>> >>> Good to know. The problem was then I did not check the array bounds. >>> Odd though, I did not think the values could be out of bounds.. >>> >>> On 3/29/12 7:24 AM, Dominique Prunier wrote: >>>> Hi John, >>>> >>>> I ran the query with r507, and apparently, the problem was there: >>>> >>>> ==14864== Invalid read of size 8 >>>> ==14864== at 0x550067A: ibis::index::sumBins(ibis::array_t<unsigned >>>> int> const&, ibis::bitvector&) const (index.cpp:6371) >>>> ==14864== by 0x576E76D: ibis::category::patternSearch(char const*, >>>> ibis::bitvector&) const (category.cpp:871) >>>> ==14864== by 0x509933C: ibis::part::patternSearch(ibis::qLike const&, >>>> ibis::bitvector&) const (part.cpp:3260) >>>> ==14864== by 0x545FF03: ibis::query::doEvaluate(ibis::qExpr const*, >>>> ibis::bitvector const&, ibis::bitvector&) const (query.cpp:3962) >>>> ==14864== by 0x545B63D: ibis::query::computeHits() (query.cpp:2771) >>>> ==14864== by 0x5452413: ibis::query::evaluate(bool) (query.cpp:847) >>>> ==14864== by 0x587328C: fastbit_build_query (capi.cpp:477) >>>> ==14864== by 0x4030F8: main (main.cpp:38) >>>> >>>> In r508, the problem is gone ! >>>> >>>> Thanks, >>>> >>>> -----Original Message----- >>>> From: K. John Wu [mailto:[email protected]] >>>> Sent: Thursday, March 29, 2012 12:33 AM >>>> To: Dominique Prunier >>>> Cc: FastBit Users >>>> Subject: Re: [FastBit-users] PATCH: perf boost on top of r501 >>>> >>>> Hi, Dominique, >>>> >>>> The stack trace shows that it is invoking a copy constructor of the >>>> ibis::bitvector class when it encountered the seg fault. Not sure >>>> what is the problem here. I have tried to reproduce the problem by >>>> modifying an existing test suite check-maurel. However, the code >>>> seems to work. >>>> >>>> There is a minor change ibis::index::sumBins to check that the >>>> incoming array contains only values less than bits.size() (the number >>>> of bitvectors stored in an index object - ibis::direkte is an index >>>> object). This might prevent attempting to out-of-bound accesses. The >>>> change is in SVN Revision 508. >>>> >>>> If you are able to find more information. Please let me know. >>>> >>>> John >>>> >>>> >>>> On 3/28/12 2:07 PM, Dominique Prunier wrote: >>>>> Woops, r507 segfaults right away in: >>>>> >>>>> C [libfastbit.so.0.0.9+0x800fbb] >>>>> ibis::bitvector::bitvector(ibis::bitvector const&)+0x23 >>>>> C [libfastbit.so.0.0.9+0x6d16c1] >>>>> ibis::index::sumBins(ibis::array_t<unsigned> const&, ibis::bitvector&) >>>>> const+0x103 >>>>> C [libfastbit.so.0.0.9+0x93f76e] ibis::category::patternSearch(char >>>>> const*, ibis::bitvector&) const+0x3c8 >>>>> C [libfastbit.so.0.0.9+0x26a33d] ibis::part::patternSearch(ibis::qLike >>>>> const&, ibis::bitvector&) const+0xcf >>>>> C [libfastbit.so.0.0.9+0x630f04] ibis::query::doEvaluate(ibis::qExpr >>>>> const*, ibis::bitvector const&, ibis::bitvector&) const+0xe1a >>>>> C [libfastbit.so.0.0.9+0x62c63e] ibis::query::computeHits()+0x356 >>>>> C [libfastbit.so.0.0.9+0x623414] ibis::query::evaluate(bool)+0x4a6 >>>>> C [libfastbit.so.0.0.9+0xa4428d] float+0x3c0 >>>>> C [jna1347076628273574295.tmp+0x11b20] float+0x4c >>>>> >>>>> I'll try to investigate this latter but the last query of my tests it >>>>> executed was >>>>> >>>>> SELECT weird_category FROM /tmp/junit8378310225719591578 WHERE >>>>> weird_category LIKE '"val\\%' >>>>> >>>>> I'll try to investigate this, but it might be related to the fact that >>>>> this query is supposed to return no result. >>>>> >>>>> Thanks, >>>>> >>>>> -----Original Message----- >>>>> From: [email protected] >>>>> [mailto:[email protected]] On Behalf Of Dominique >>>>> Prunier >>>>> Sent: Wednesday, March 28, 2012 4:58 PM >>>>> To: K. John Wu >>>>> Cc: FastBit Users >>>>> Subject: Re: [FastBit-users] PATCH: perf boost on top of r501 >>>>> >>>>> Hey John, >>>>> >>>>> I'll have a look to r507, probably tomorrow. To limit the risk, i've >>>>> chosen the well tested r506 as my stable version using the >>>>> FASTBIT_EMPTY_STRING_AS_NULL define. >>>>> >>>>> My problem with null mask is that i write my partitions in pure Java >>>>> code. It is quite straightforward to write data files and -part.txt, but >>>>> writing a NULL mask is something else. Besides, I don't really need a >>>>> difference between NULL and empty anyway, since treating empty strings as >>>>> NULLs is no different than some RDBMS engines that we support (Oracle >>>>> does that for example). >>>>> >>>>> I have one quick question about category columns. Do they really have a >>>>> separate NULL mask or do they use the bitmap stored at key 0 as their >>>>> NULL mask ? If so, that means that keeping the >>>>> FASTBIT_EMPTY_STRING_AS_NULL would allow me to indirectly build some real >>>>> NULL values which would work with the NOT NULL syntax (which, by the way, >>>>> in SQL is IS NOT NULL/IS NULL, maybe it would be worth changing it). >>>>> >>>>> Thanks, >>>>> >>>>> -----Original Message----- >>>>> From: K. John Wu [mailto:[email protected]] >>>>> Sent: Wednesday, March 28, 2012 3:26 PM >>>>> To: Dominique Prunier >>>>> Cc: FastBit Users >>>>> Subject: Re: [FastBit-users] PATCH: perf boost on top of r501 >>>>> >>>>> Hi, Dominique, >>>>> >>>>> I have added code to accept "colname NOT NULL" in the where clauses. >>>>> The new code is in SVN Revision 507. >>>>> >>>>> The new revision should also consolidate the handling of many >>>>> bitvectors in category::patternSearch and address the issue of >>>>> possibly missing calls to index::activate (which leads to incorrect >>>>> answers). >>>>> >>>>> You can input null values through tablex::readCSV. There is an >>>>> example in tests/Makefile.am in the way it generates data partition >>>>> w7. The test case 15 of really-small also makes use of the new >>>>> expression "NOT NULL". >>>>> >>>>> Let me know if you spot any problems. >>>>> >>>>> John >>>>> >>>>> >>>>> On 3/28/12 10:45 AM, Dominique Prunier wrote: >>>>>> Hey John, >>>>>> >>>>>> My guess is that empty strings are used more often that we'd think for >>>>>> the same use case: use them as NULL marker because it is the easiest way >>>>>> to both insert and query (which is exactly what i use them for). Even if >>>>>> it is not an exact synonym of the SQL NULL (especially for propagation), >>>>>> for most use cases, it is close enough. The fact that its key is fixed >>>>>> and well known provides a valid workaround to simulate IS NULL/IS NOT >>>>>> NULL predicates and since it is excluded from most string related >>>>>> predicates (most importantly, a LIKE '%' wont select it), it is a quite >>>>>> easy and intuitive to use. >>>>>> >>>>>> Besides, the column data file for strings can't represent NULL values so >>>>>> you would have to deal with null masks, which make things significantly >>>>>> more complex (especially, to create a partition from scratch without >>>>>> using the FastBit library) and potentially more resource hungry (have to >>>>>> read/write null mask, ...). >>>>>> >>>>>> That being said, my only problem with making the distinction between >>>>>> NULL and empty in the dictionary is the current revision's inability to >>>>>> query empty strings and/or NULLs (which is currently worked around by >>>>>> the uint alternative, =0) and the fact that it matches a pattern like >>>>>> '%'. Since there is no guarantee on the empty string key, i don't have >>>>>> any workaround for now. >>>>>> >>>>>> For the time being, i'll stick with the FASTBIT_EMPTY_STRING_AS_NULL >>>>>> define waiting for the ambiguity to vanish. >>>>>> >>>>>> Thanks, >>>>>> >>>>>> -----Original Message----- >>>>>> From: K. John Wu [mailto:[email protected]] >>>>>> Sent: Wednesday, March 28, 2012 1:22 PM >>>>>> To: Dominique Prunier >>>>>> Cc: FastBit Users >>>>>> Subject: Re: [FastBit-users] PATCH: perf boost on top of r501 >>>>>> >>>>>> The ability to distinguish between empty string and null string can be >>>>>> useful. The ambiguity in the current code is related to some earlier >>>>>> design oversight, which we intend to correct. My hope is that not too >>>>>> many people have empty strings that want to do something with, so >>>>>> breaking this compatibility is not a big deal. >>>>>> >>>>>> There are also a problem with the implementation of >>>>>> category::patternSearch that neglects to read the bitmaps from index >>>>>> files (neglecting to call index::activate). I am consolidating some >>>>>> code to make use of the existing strategies involving summation of a >>>>>> large number of bitmaps in ibis::index::sumBits and >>>>>> ibis::index::sumBins. These functions should encapsulate the idea of >>>>>> when to decompress bitmaps a lot better than the simple version >>>>>> currently in category::patternSearch. >>>>>> >>>>>> I am doing tests now and will let everyone know when I am ready to >>>>>> check the code in. >>>>>> >>>>>> John >>>>>> >>>>>> >>>>>> On 3/28/12 8:44 AM, Dominique Prunier wrote: >>>>>>> Thanks John for your help. It is always very appreciated. >>>>>>> >>>>>>> With the macro FASTBIT_EMPTY_STRING_AS_NULL enabled, all my test cases >>>>>>> now works. I'll test performance next but it could be a good candidate >>>>>>> for my stable version. >>>>>>> >>>>>>> About the FASTBIT_EMPTY_STRING_AS_NULL, what do you think would be the >>>>>>> best default ? For my use case, it is obviously to enable it, but for >>>>>>> everybody else i don't know. My concern is the backward compatibility >>>>>>> here, especially the fact that it influences the index creation, and >>>>>>> not usage. This means that somebody who upgrades won't notice this >>>>>>> change before it regenerates indexes. What's your opinion on this ? >>>>>>> >>>>>>> Thanks, >>>>>>> >>>>>>> -----Original Message----- >>>>>>> From: K. John Wu [mailto:[email protected]] >>>>>>> Sent: Wednesday, March 28, 2012 11:20 AM >>>>>>> To: Dominique Prunier >>>>>>> Cc: FastBit Users >>>>>>> Subject: Re: [FastBit-users] PATCH: perf boost on top of r501 >>>>>>> >>>>>>> Hi, Dominique, >>>>>>> >>>>>>> Thanks for the suggestions and and test cases. Just checked in a set >>>>>>> of changes as SVN Revision 506. Here is a bit more explanation. >>>>>>> >>>>>>> On item 1, I have taken the option you've suggested in the first >>>>>>> message, i.e., use the macro FASTBIT_EMPTY_STRING_AS_NULL >>>>>>> >>>>>>> On item 2, I have restored the escaping of using backslash as you >>>>>>> requested. >>>>>>> >>>>>>> Will go through you tests cases next and see what else I need to change. >>>>>>> >>>>>>> John >>>>>>> >>>>>>> >>>>>>> On 3/28/12 8:02 AM, Dominique Prunier wrote: >>>>>>>> Hi John, >>>>>>>> >>>>>>>> Here is two simple test cases for my two issues with r505. >>>>>>>> >>>>>>>> 1. empty-strings.zip: there is no way to select empty string anymore >>>>>>>> >>>>>>>> **** FAILED (bad result count) with where clause << a='' >> >>>>>>>> >>>>>>>> **** FAILED (bad result count) with where clause << a=0 >> >>>>>>>> >>>>>>>> **** FAILED (hard) with where clause << a LIKE '' >> >>>>>>>> >>>>>>>> 2. de-escaping.zip: there is no way to select a string with a reserved >>>>>>>> char in it >>>>>>>> >>>>>>>> **** FAILED (bad result count) with where clause << a='it\'s good' >> >>>>>>>> >>>>>>>> Warning -- ibis::whereParser encountered syntax error, unexpected name >>>>>>>> string at location a='it's good':1.7 >>>>>>>> Warning -- query[96w0-3xn8Tg----1]::setWhereClause -- failed to parse >>>>>>>> the WHERE clause "a='it's good'" >>>>>>>> Warning -- fastbit_build_query failed to assign conditions (a='it's >>>>>>>> good') to a query >>>>>>>> **** FAILED (hard) with where clause << a='it's good' >> >>>>>>>> >>>>>>>> Warning -- ibis::whereParser encountered syntax error, unexpected >>>>>>>> $undefined at location a=it's good:1.5 >>>>>>>> Warning -- query[96w0-3xn8Tg----2]::setWhereClause -- failed to parse >>>>>>>> the WHERE clause "a=it's good" >>>>>>>> Warning -- fastbit_build_query failed to assign conditions (a=it's >>>>>>>> good) to a query >>>>>>>> **** FAILED (hard) with where clause << a=it's good >> >>>>>>>> >>>>>>>> With the attached patch, it fixes my test cases (except a LIKE '' that >>>>>>>> didn't work before and a='it's good' and a=it's good whieh are invalid >>>>>>>> where clauses). >>>>>>>> >>>>>>>> Thanks, >>>>>>>> >>>>>>>> -----Original Message----- >>>>>>>> From: [email protected] >>>>>>>> [mailto:[email protected]] On Behalf Of Dominique >>>>>>>> Prunier >>>>>>>> Sent: Wednesday, March 28, 2012 10:04 AM >>>>>>>> To: K. John Wu >>>>>>>> Cc: FastBit Users >>>>>>>> Subject: Re: [FastBit-users] PATCH: perf boost on top of r501 >>>>>>>> >>>>>>>> Hey John, >>>>>>>> >>>>>>>> I'm trying r505 right know, i have two questions/remarks: >>>>>>>> >>>>>>>> 1. I saw a change about the dictionary now able to accept empty >>>>>>>> strings and treat them as normal strings instead of NULLs. This breaks >>>>>>>> quite a lot of my test cases, specifically those which used to test >>>>>>>> category=0 or !=0 to simulate the IS NULL/IS NOT NULL because testing >>>>>>>> for an empty string doesn't work (='' or LIKE '' used to fail or >>>>>>>> return invalid results). What would be your recommendation for that >>>>>>>> use case ? Could we add a define for those relying on this behavior ? >>>>>>>> Something like: >>>>>>>> >>>>>>>> - //if (*str == 0) return 0; >>>>>>>> +#ifdef FASTBIT_EMPTY_STRING_AS_NULL >>>>>>>> + if (*str == 0) return 0; >>>>>>>> +#endif >>>>>>>> >>>>>>>> 2. I can't find anywhere the de-escaping patch in r505, am i missing >>>>>>>> something ? >>>>>>>> >>>>>>>> Thanks, >>>>>>>> >>>>>>>> -----Original Message----- >>>>>>>> From: K. John Wu [mailto:[email protected]] >>>>>>>> Sent: Wednesday, March 28, 2012 1:55 AM >>>>>>>> To: Dominique Prunier >>>>>>>> Cc: FastBit Users >>>>>>>> Subject: Re: [FastBit-users] PATCH: perf boost on top of r501 >>>>>>>> >>>>>>>> Hi, Dominique, >>>>>>>> >>>>>>>> There are some updates to involving merge of dictionaries and to >>>>>>>> exercise the operations involving unmatched quotes. The new code is >>>>>>>> SVN R505. >>>>>>>> >>>>>>>> Please let me know if you have any additional questions. >>>>>>>> >>>>>>>> John >>>>>>>> >>>>>>>> >>>>>>>> On 3/27/12 1:03 PM, Dominique Prunier wrote: >>>>>>>>> Hey John, >>>>>>>>> >>>>>>>>> There is definitely a need for FastBit escaping. The escaping problem >>>>>>>>> is not at the shell level (though we could have one there) since in >>>>>>>>> pure C/C++ code, there's no shell involved when i'm building a where >>>>>>>>> clause from a string. The problem is at the where clause parsing >>>>>>>>> level (in the lexer to be more precise) to be able to express string >>>>>>>>> literals among other things (and not only metas, it is also white >>>>>>>>> spaces, ...). >>>>>>>>> Typically, my test that fails is as simple as calling >>>>>>>>> fastbit_build_query(..., ..., "a='it\\'s good'"). This is expected to >>>>>>>>> create a qString << a = it's good >> but now, it creates a qString << >>>>>>>>> a = it\'s good >> which is wrong. The attached patch restores the >>>>>>>>> descaping, but _not_ the double quote stripping (because it is >>>>>>>>> already handled in the lexer). All my test cases works after applying >>>>>>>>> it on r503. >>>>>>>> >>>>>>>> The constructors for ibis::qString and ibis::qLike really should not >>>>>>>> strip away anything. In your case, you should be able to do the >>>>>>>> following >>>>>>>> >>>>>>>> .../tcapi data-dir "a=\"it's good\"" >>>>>>>> >>>>>>>> if you are using fastbit_build_query, you can use the same string >>>>>>>> fastbit_build_query(..., ..., "a=\"it's good\""); >>>>>>>> >>>>>>>> Since FastBit regular expression only support four meta characters ? * >>>>>>>> _ %. There is no need to escape anything. It is probably cleaner to >>>>>>>> not introduce stripping of anything special (except the outer most >>>>>>>> quotes, which should be only done once). >>>>>>>> >>>>>>>>> >>>>>>>>> About the decompression, thanks for the link, this is very >>>>>>>>> interesting stuff ! But my point here is not about questing the fact >>>>>>>>> the decompression can be better is some case, i was just under the >>>>>>>>> impression that the hit vector given to category::patternSearch was >>>>>>>>> _always_ already decompressed since it is ultimately a bitvector that >>>>>>>>> has been created from scratch for query evaluation (it would need >>>>>>>>> verification though). My guess is that the few percent of performance >>>>>>>>> i'm loosing here are attributable to the check (hits.isCompressed() >>>>>>>>> && hits.bytes()*mult + bv->bytes() > hits.size()), since it gets >>>>>>>>> executed _A LOT_ of times. I'll try to investigate it a little bit >>>>>>>>> further. >>>>>>>> >>>>>>>> I have rearranged the tests for decompression in layers which >>>>>>>> hopefully will eliminate the need to perform more expensive tests in >>>>>>>> your case that presumably involve a fairly small number of values. >>>>>>>> _______________________________________________ >>>>>>>> FastBit-users mailing list >>>>>>>> [email protected] >>>>>>>> https://hpcrdm.lbl.gov/cgi-bin/mailman/listinfo/fastbit-users >>>>> _______________________________________________ >>>>> FastBit-users mailing list >>>>> [email protected] >>>>> https://hpcrdm.lbl.gov/cgi-bin/mailman/listinfo/fastbit-users _______________________________________________ FastBit-users mailing list [email protected] https://hpcrdm.lbl.gov/cgi-bin/mailman/listinfo/fastbit-users
