Re: [Firebird-devel] Start transaction from base transaction
On 24/02/2019 08:23, Vlad Khorsun wrote: > TPB: isc_tpb_snapshot_commit_number, isc_tpb_snapshot_number Regards, Vlad PS we also must add isc_info_tra_snapshot_number and, probably, context variable. Don't we already have context SNAPSHOT_CN? It already has the same meaning of the new feature, so therefore what context you would want to add? SNAPSHOT_CN returns snapshot number of current request if transaction is read-committed read consistency (RCRC). But... after more thinking i consider it is ok to use it for snapshot cloning. Additional variable returning NULL for RCRC transactions will add more confusing. From the other side - there is no problem to clone any kind of existing snapshot. Users must be warned that snapshot transaction which cloned request-level snapshot of another RCRC transaction will see same data at base request and subsequent requests in the base RCR transaction could see another data. Yes, and that is already possible as an implementation side effect. It should be extremely discouraged, except for cases like long running request detected via monitoring that one wants to debug in another connection. I also suggest that new isc_info_tra_snapshot_number returns the same data as SNAPSHOT_CN variable. Yes, no problem. But for RC it will be NULL as there is no request. And then SNAPSHOT_CN means "SNAPSHOT COMMIT NUMBER", it's the reason for the syntax that I offered. We can change it, if needed. Note, I introduced two variables: GLOBAL_CN and SNAPSHOT_CN and its names looks logical and consistent to me (at least at that time). I see no problem to change names to something better. Yes, the names must match as SNAPSHOT_CN means same thing as the clause passed to SET TRANSACTION. Adriano Firebird-Devel mailing list, web interface at https://lists.sourceforge.net/lists/listinfo/firebird-devel
Re: [Firebird-devel] Start transaction from base transaction
24.02.2019 12:37, Dimitry Sibiryakov wrote: 24.02.2019 3:23, Adriano dos Santos Fernandes wrote: maybe: SET TRANSACTION SNAPSHOT [USING SNAPSHOT ] or SET TRANSACTION SNAPSHOT [USING SNAPSHOT NUMBER ] What I dislike here is double SNAPSHOT words. You can make it optional. No objection from my side Regards, Vlad Firebird-Devel mailing list, web interface at https://lists.sourceforge.net/lists/listinfo/firebird-devel
Re: [Firebird-devel] Start transaction from base transaction
24.02.2019 4:23, Adriano dos Santos Fernandes wrote: On Sat, Feb 23, 2019, 21:30 Vlad Khorsun wrote: 23.02.2019 21:14, Adriano dos Santos Fernandes wrote: > Hi! > > After changes to use commit number instead of base transaction number, I > offer to make that interfaces for the feature: I offer to not introduce additional confusing with different usages of commit numbers. Commit Number (CN) itself is an unique value assigned to the every committed transaction. The source of that value is per-database counter. When some database snapshot is created it uses current value of database counter of commit numbers as own identifier. Lets name it Snapshot Number (SN) to distinguish from Commit Number assigned to transaction. The sourse of CN and SN is the same, but usage and meaning is very different ! Therefore > SQL command: SET TRANSACTION SNAPSHOT COMMIT NUMBER > > (some variant as SNAPSHOT FROM COMMIT NUMBER or SNAPSHOT BASE COMMIT > NUMBER may be acceptable) maybe: SET TRANSACTION SNAPSHOT [USING SNAPSHOT ] or SET TRANSACTION SNAPSHOT [USING SNAPSHOT NUMBER ] What I dislike here is double SNAPSHOT words. Same concerns here > TPB: isc_tpb_snapshot_commit_number, isc_tpb_snapshot_number Regards, Vlad PS we also must add isc_info_tra_snapshot_number and, probably, context variable. Don't we already have context SNAPSHOT_CN? It already has the same meaning of the new feature, so therefore what context you would want to add? SNAPSHOT_CN returns snapshot number of current request if transaction is read-committed read consistency (RCRC). But... after more thinking i consider it is ok to use it for snapshot cloning. Additional variable returning NULL for RCRC transactions will add more confusing. From the other side - there is no problem to clone any kind of existing snapshot. Users must be warned that snapshot transaction which cloned request-level snapshot of another RCRC transaction will see same data at base request and subsequent requests in the base RCR transaction could see another data. I also suggest that new isc_info_tra_snapshot_number returns the same data as SNAPSHOT_CN variable. And then SNAPSHOT_CN means "SNAPSHOT COMMIT NUMBER", it's the reason for the syntax that I offered. We can change it, if needed. Note, I introduced two variables: GLOBAL_CN and SNAPSHOT_CN and its names looks logical and consistent to me (at least at that time). I see no problem to change names to something better. Regards, Vlad PS As for me, "Snapshot Commit Number" is full name for (more usable) "Snapshot Number". "Snapshot CN" just another way to make full name shorter. We need to choose some consistent way to name the things before final release. Firebird-Devel mailing list, web interface at https://lists.sourceforge.net/lists/listinfo/firebird-devel
Re: [Firebird-devel] Start transaction from base transaction
24.02.2019 3:23, Adriano dos Santos Fernandes wrote: maybe: SET TRANSACTION SNAPSHOT [USING SNAPSHOT ] or SET TRANSACTION SNAPSHOT [USING SNAPSHOT NUMBER ] What I dislike here is double SNAPSHOT words. You can make it optional. -- WBR, SD. Firebird-Devel mailing list, web interface at https://lists.sourceforge.net/lists/listinfo/firebird-devel
