From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from localhost (localhost [127.0.0.1]) by turing.freelists.org (Avenir Technologies Mail Multiplex) with ESMTP id 6EC0923547 for ; Mon, 23 Jul 2018 14:29:16 -0400 (EDT) Received: from turing.freelists.org ([127.0.0.1]) by localhost (turing.freelists.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id p46452iosSr9 for ; Mon, 23 Jul 2018 14:29:16 -0400 (EDT) Received: from smtp57.i.mail.ru (smtp57.i.mail.ru [217.69.128.37]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by turing.freelists.org (Avenir Technologies Mail Multiplex) with ESMTPS id ABFD923334 for ; Mon, 23 Jul 2018 14:29:15 -0400 (EDT) Subject: [tarantool-patches] Re: [PATCH v1 1/1] sql: prevent executing crossengine sql References: <6134a0afdcfba13ca289e2d42fdd529a2787070a.1532094680.git.kshcherbatov@tarantool.org> <50ac96b7-d395-f528-f66b-c10847e54670@tarantool.org> <812d64bf-a5a8-805d-d353-32f6733a41b9@tarantool.org> <26691970-9406-1cd2-e2ea-3e78b4d7b145@tarantool.org> <462DD32C-45A7-48FB-8FB1-58D4DA85C553@tarantool.org> From: Vladislav Shpilevoy Message-ID: <5899c7db-b1c0-d099-989e-dcb41b801cdd@tarantool.org> Date: Mon, 23 Jul 2018 21:29:13 +0300 MIME-Version: 1.0 In-Reply-To: <462DD32C-45A7-48FB-8FB1-58D4DA85C553@tarantool.org> Content-Type: text/plain; charset="utf-8"; format="flowed" Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: tarantool-patches-bounce@freelists.org Errors-to: tarantool-patches-bounce@freelists.org Reply-To: tarantool-patches@freelists.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: tarantool-patches List-subscribe: List-owner: List-post: List-archive: To: "n.pettik" , tarantool-patches@freelists.org Cc: Kirill Shcherbatov On 23/07/2018 21:06, n.pettik wrote: > >>>>>> 2. I strongly do not like these 3 checks. >>>>>> >>>>>> * space->id == 0 can be skipped, since begin_ro_stmt needs >>>>>> only space engine. >>>>>> >>>>>> * id != stat4/1 is a huge crutch that should be removed. The >>>>>> later will be dilapidated by any stat or tx manager change. >>>>>> I guess it is because of ANALYZE that scans spaces and then >>>>>> updates _stat1/4. But I can not understand, why it can not >>>>>> firstly read the samples from user spaces, commit ro, and >>>>>> secondly insert the samples into stats in another transaction. >>>>>> Besides, I believe, that user spaces and analyze ones should >>>>>> not be in a single transaction ever as former are actually >>>>>> system ones and should not be mixed with user spaces. >>>>>> Nikita, I appeal to you for onlooking. Is it possible to >>>>>> split ANALYZE in two transactions? How could Kirill do it? >>>>>> Besides there is another option, but IMHO it could seem even >>>>>> more flawed. >>>>> Why do you think so? >>>> >>>> I am afraid of additional 'if's for such internal thing. >>>> >>>>> Actually, I can’t come up with better solution: >>>>> when we start executing OP_AnalysisLoad we always start transaction >>>>> (member that issue with gathering statistics on region to make it consistent? >>>>> See sql_analysis_load()). >>>> >>>> I think that on insertion into analyze spaces we correctly start a >>>> transaction, and it is not for region usage only. As I remember, >>>> there were problems with stat spaces consistency if we update stat >>>> not in a transaction. Region is just a convenient benefit. >>> It is not an insertion: OP_AnalysisLoad executes SELECT from >>> stat spaces, and before those SELECTs we start transaction. >>>>> Mb we always can avoid calling txn_begin_ro_stmt() on system spaces? >>>> >>>> It is okay, but for ephemeral spaces too, it is not? >>> Then, I don’t understand why we can’t avoid calling it for any memtx space? >> >> Because when we start a transaction, we expect a kind of read-view, >> conflict resolving, serialization. But in a case of memtx we can not >> provide each of these things after a yield. So memtx and vinyl >> DDL/DML/DQL should not get in touch in a transaction. >> >> If a transaction touches vinyl, then yields are possible and memtx >> is unable to deal with them. >> >> For memtx txn_begin_ro_stmt only checks that engine is not changed. >> >> For vinyl txn_begin_ro_stmt does more - it creates vinyl-internal >> transaction object, remembers current read-view LSN etc. >> >>> As far as I see (before this patch) we don’t call txn_begin_ro_stmt() at all. >> >> And this is why we got the bug. >> >>>> On the parsing >>>> stage we know is the space system one or not. Besides, I think that if >>>> a user calls explicit "SELECT * FROM _space", we should begin ro, >>>> but not when we open an internal cursor (ephemeral, or to insert into >>>> stats or something). It looks like a good question for the server >>>> team chat - should be start read-only statements on explicit SELECT >>>> from a system space? Box API now does it (inside box_index_iterator()). >>>> >>>>> Quite similar to this issue might be CREATE TABLE AS SELECT >>>>> when it will be implemented. However, in this case we still can avoid >>>>> mixing user and system spaces within one transaction: >>>>> INSERT TO _SPACE/_INDEX etc >>>>> SELECT FROM source INSERT TO ephemeral >>>>> START TRANSACTION >>>>> SELECT FROM ephemeral INSERT TO destination >>>>> COMMIT TRANSACTION >>>> >>>> Then I do not understand why can not we do the same for ANALYZE: >>>> >>>> SELECT samples from different engines with no ro stmts; >>>> START TX; >>>> INSERT tuples into stat1/4; >>>> COMMIT; >>> Look how things happen: >>> 1. SELECT samples from different engines INSERT INTO ephemeral space >>> (It doesn’t matter with or without ro stmt since there is no active transaction); >>> 2. SELECT from ephemeral space INSERT INTO _stat spaces; >>> 3. START TX; >>> 4. SELECT FROM _stat space INSERT INTO tarantool data-dictionary >>> (i.e. fill index->def->opts->stat with current statistics); >> >> Then I did not get it. From your words, after step 3 we use only >> ephemeral spaces and stat1/4, but all of them are memtx. At the >> same time when I remove id != stat1/4 check from the Kirill's >> patch, I see errors about multi-engine transactions. > > My initial thought after your explanation concerning txn_begin_ro_stmt() work > seems to be wrong. However, it really fails on execution sql_analysis_load(): > The reason seems to be call of box_space_id_by_name(). > I set br on diag_set(): > > * frame #0: 0x00000001000d3d00 tarantool`diag_add_error(diag=0x0000000104800250, e=0x0000000104c90c68) at diag.h:172 > frame #1: 0x00000001000d3eab tarantool`txn_begin_in_engine(engine=0x000000010294ae80, txn=0x000000010480c038) at txn.c:160 > frame #2: 0x0000000100012e09 tarantool`txn_begin_ro_stmt(space=0x0000000104c85ba0, txn=0x000000010481edf8) at txn.h:264 > frame #3: 0x0000000100012c67 tarantool`::box_index_get(space_id=281, index_id=2, key="?M\x04\x01", key_end="\x04\x01", result=0x000000010481ee90) at index.cc:247 > frame #4: 0x00000001000db6f8 tarantool`::box_space_id_by_name(name="M", len=1) at box.cc:959 > frame #5: 0x000000010036fbde tarantool`analysis_loader(data=0x000000010481f130, argc=3, argv=0x000000011d809020, unused=0x000000011d809008) at analyze.c:1250 > frame #6: 0x000000010039fbdb tarantool`sqlite3_exec(db=0x0000000102d343f8, zSql="SELECT \"tbl\",\"idx\",\"stat\" FROM \"_sql_stat1\"", xCallback=(tarantool`analysis_loader at analyze.c:1242), pArg=0x000000010481f130, pzErrMsg=0x0000000000000000) at legacy.c:139 > frame #7: 0x000000010036f50c tarantool`sql_analysis_load(db=0x0000000102d343f8) at analyze.c:1734 > frame #8: 0x00000001003e7b25 tarantool`sqlite3VdbeExec(p=0x000000011d80c808) at vdbe.c:4778 > frame #9: 0x00000001003eb75c tarantool`sqlite3Step(p=0x000000011d80c808) at vdbeapi.c:570 > > One engine is memtx, another is sys view. > I guess it would be easy to fix: just use schema_find_id. > Kirill, please, try to fix this in that way. If you succeeded we could defer this complex cross-engine things on later times and now just always begin ro stmt.