From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtpng2.m.smailru.net (smtpng2.m.smailru.net [94.100.179.3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dev.tarantool.org (Postfix) with ESMTPS id DE2FC46970E for ; Wed, 22 Jan 2020 16:54:12 +0300 (MSK) Date: Wed, 22 Jan 2020 16:54:09 +0300 From: Nikita Pettik Message-ID: <20200122135409.GB1144@tarantool.org> References: <3f49ddc14c2e07f4ac96fc71f3912fd0c5663882.1579032293.git.korablev@tarantool.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <3f49ddc14c2e07f4ac96fc71f3912fd0c5663882.1579032293.git.korablev@tarantool.org> Subject: Re: [Tarantool-patches] [PATCH] box: rfc for stacked diagnostic area List-Id: Tarantool development patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: tarantool-patches@dev.tarantool.org Cc: v.shpilevoy@tarantool.org On 14 Jan 23:16, Nikita Pettik wrote: > From: Kirill Shcherbatov Hi guys, Does anybody want to look at this RFC? It's quite similar to the one which got LGTM from Konstantin, but it is even more simplified. I have to get formal approvement to start fixing code itself. Thanks. > Part of #1148 > --- > rfc in human-readable format: https://github.com/tarantool/tarantool/blob/np/gh-1148-stacked-diag/doc/rfc/1148-stacked-diagnostics.md > Previous version of rfc: https://github.com/tarantool/tarantool/commit/c2a7e1a10732fdb231780ac04d1a4bc1618c0468 > > Changes in this version: > - All savepoint routines have been removed as meaningless; > - Removed SQL warnings mentions since they are unrelated to the subject of rfc; > - Removed mentions about exposing box.error.new() with filename and > line parameters (again, it is barely related to the subject of rfc); > - Described in details difference between diag_set() in diag_add() > functions as a part of C interface; > - Other minor clean-ups. > > Now RFC looks quite brief and straightforward in its implementation; > it attempts at solving only #1148 issue. > > doc/rfc/1148-stacked-diagnostics.md | 214 ++++++++++++++++++++++++++++++++++++ > 1 file changed, 214 insertions(+) > create mode 100644 doc/rfc/1148-stacked-diagnostics.md > > diff --git a/doc/rfc/1148-stacked-diagnostics.md b/doc/rfc/1148-stacked-diagnostics.md > new file mode 100644 > index 000000000..68fa6d21a > --- /dev/null > +++ b/doc/rfc/1148-stacked-diagnostics.md > @@ -0,0 +1,214 @@ > +# Stacked Diagnostics > + > +* **Status**: In progress > +* **Start date**: 30-07-2019 > +* **Authors**: Kirill Shcherbatov @kshcherbatov kshcherbatov@tarantool.org, > + Pettik Nikita korablev@tarantool.org > +* **Issues**: [#1148](https://github.com/tarantool//issues/1148) > + > +## Background and motivation > + > +Support stacked diagnostics for Tarantool allows to accumulate all errors > +occurred during request processing. It allows to better understand what > +happened, and handle errors appropriately. > + > +### Current error diagnostics > + > +Currently Tarantool has `diag_set()` mechanism to set a diagnostic error. > +Object representing error featuring following properties: > + - type (string) error’s C++ class; > + - code (number) error’s number; > + - message (string) error’s message; > + - file (string) Tarantool source file; > + - line (number) line number in the Tarantool source file. > + > +The last error raised is exported with `box.error.last()` function. > + > +Type of error is represented by a few C++ classes (all are inherited from > +Exception class): > +``` > +ClientError > + | LoggedError > + | AccessDeniedError > + | UnsupportedIndexFeature > + > +XlogError > + | XlogGapError > + > +SystemError > + | SocketError > + | OutOfMemory > + | TimedOut > + > +ChannelIsClosed > +FiberIsCancelled > +LuajitError > +IllegalParams > +CollationError > +SwimError > +CryptoError > +``` > + > +All codes and names of ClientError class are available in box.error. > +User is able to create a new error instance of predefined type using > +box.error.new() function. For example: > +``` > +tarantool> t = box.error.new(box.error.CREATE_SPACE, "myspace", "just cause") > +tarantool> t:unpack() > +--- > +- type: ClientError > + code: 9 > + message: 'Failed to create space ''myspace'': just because' > + trace: > + - file: '[string "t = box.error.new(box.error.CREATE_SPACE, "my..."]' > + line: 1 > +``` > + > +User is also capable of defining own errors with any code by means of: > +``` > +box.error.new({code = user_code, reason = user_error_msg}) > +``` > +For instance: > +``` > +e = box.error.new({code = 500, reason = 'just cause'}) > +``` > + > +Error cdata object has `:unpack()`, `:raise()`, `:match(...)`, `:__serialize()` > +methods and `.type`, `.message` and `.trace` fields. > + > +## Proposal > + > +In some cases a diagnostic information should be more complicated than > +one last raised error. Consider following example: persistent Lua function > +referenced by functional index has a bug in it's definition, Lua handler sets > +an diag message. Then functional index extractor code setups an own, more > +specialized error. Without stacked diagnostic area, only last error is > +delivired to user. One way to deal with this problem is to introduce stack > +accumulating all errors happened during request processing. > + > +### C API > + > +Let's keep existent `diag_set()` method as is. It is supposed to replace the > +last error in diagnostic area with a new one. To add new error at the top of > +existing one, let's introduce new method `diag_add()`. It is assumed to keep > +an existent error message in diagnostic area (if any) and sets it as a reason > +error for a recently-constructed error object. Note that `diag_set()` is not > +going to preserve pointer to previous error which is held in error to be > +substituted. To illustrate last point consider example: > + > +``` > +0. Errors: > +1. diag_set(code = 1) > +Errors: NULL> > +2. diag_add(code = 2) > +Errors: e2(code = 2) -> NULL> > +3. diag_set(code = 3) > +Errors: NULL> > +``` > + > +Hence, developer takes responsibility of placing `diag_set()` where the most > +basic error should be raised. For instance, if during request processing > +`diag_add()` is called before `diag_set()` then it will result in inheritance > +of all errors from previous error raise: > + > +``` > +-- Processing of request #1 > +1. diag_set(code = 1) > +Errors: NULL> > +2. diag_add(code = 2) > +Errors: e2(code = 2) -> NULL> > +-- End of execution > + > +-- Processing of request #2 > +1. diag_add(code = 1) > +Errors: e2(code = 2) -> e3(code = 1) -> NULL> > +-- End of execution > +``` > + > +As a result, at the end of execution fo second request, three errors in > +stack are reported instead of one. > + > +Another way to resolve this issue is to erase diagnostic area before > +request processing. However, it breaks current user-visible behaviour > +since box.error.last() will preserve last occurred error only until execution > +of the next request. > + > +The diagnostic area (now) contains (nothing but) pointer to the top error: > +``` > +struct diag { > + struct error *last; > +}; > + > +``` > + > +To organize errors in a list let's extend error structure with pointer to > +the previous element. Or alternatively, add member of any data structure > +providing list properties (struct rlist, struct stailq or whatever): > +``` > +struct diag { > + struct stailq *errors; > +}; > + > +struct error { > + ... > + struct stailq_entry *in_errors; > +}; > +``` > + > + > +### Lua API > + > +Tarantool returns a last-set (diag::last) error as `cdata` object from central > +diagnostic area to Lua in case of error. User should be unable to modify it > +(since it is considered to be a bad practice - in fact object doesn't belong > +to user). On the other hand, user needs an ability to inspect a collected > +diagnostic information. Hence, let's extend the `box.error` API with a function > +which provides the way to get the previous error (reason): `:prev()` (and > +correspondingly `.prev` field). > + > +``` > +-- Return a reason error object for given error > +-- (when exists, nil otherwise). > +box.error.prev(error) == error.prev > +``` > + > +Furthermore, let's extend signature of `box.error.new()` with new (optional) > +argument - the 'reason' parent error object: > + > +``` > +e1 = box.error.new({code = 111, reason = "just cause"}) > +e2 = box.error.new({code = 222, reason = "just cause x2", prev = e1}) > +``` > + > +### Binary protocol > + > +Currently errors are sent as `(IPROTO_ERROR | errcode)` response with an > +string message containing error details as a payload. There are not so many > +options to extend current protocol wihtout breaking backward compatibility > +(which is obviously one of implementation requirements). One way is to extend > +existent binary protocol with a new key IPROTO_ERROR_STACK (or > +IPROTO_ERROR_REASON or simply IPROTO_ERROR_V2): > +``` > +{ > + // backward compatibility > + IPROTO_ERROR: "the most recent error message", > + // modern error message > + IPROTO_ERROR_STACK: { > + { > + // the most recent error object > + IPROTO_ERROR_CODE: error_code_number, > + IPROTO_ERROR_REASON: error_reason_string, > + }, > + ... > + { > + // the oldest (reason) error object > + }, > + } > +} > +``` > + > +IPROTO_ERROR is always sent (as in older versions) in case of error. > +IPROTO_ERROR_STACK is presented in response only if there's at least two > +elements in diagnostic list. Map which contains error stack can be optimized > +in terms of space, so that avoid including error which is already encoded > +in IPROTO_ERROR. > -- > 2.15.1 >