Geoff Winkless. As you'd expect, I've included both isolation tests and regressiontests covering a reasonable variety of cases. INSERT ON Introduction to the PostgreSQL upsert. Once data has been added to a database, the SQL UPDATE command can be used to modify the column values in the rows of a table. I've tentatively added code to keepa buffer pin for longer, but that's probably not good enough if weassume that it's necessary at all. Prerequisites We should be able to come with reasonable behavior for atleast some of those. The optional RETURNING clause causes UPDATE to compute and return value (s) based on each row actually updated. We still dothat (unprincipled deadlocks are our only alternative), but now holdon to the pin for longer, until after tuple locking. Is anyone in this camp? A candidate row will only be inserted if that row does not violate any unique constraints. Youmay specify a unique index to merge on from within the INSERTstatement, thus avoiding the risk of inadvertently having the updateaffect the wrong tuple due to the user failing to consider that therewas a would-be unique violation within some other unique indexconstraining some other attribute. It is a very importantpoint in my opinion. This option basically helps to perform DML actions like, Insert IF not Exists, Update IF Exists. Here is a table of key, value pairs: demo=# SELECT * FROM kv; key | value -----+----- host | 127.0.0.1 port | 5432 (2 rows) A common use case is to insert a row only if it does not exist – and if it does, do not overwrite. INSERT INTO upsert (key, val) VALUES (1, 'insert') ON CONFLICT UPDATE SET val = 'update'; Essentially, the implementation has all stages of query processing track some auxiliary UPDATE state. The patch currently lacks a way of referencing datums rejected forinsertion when updating. I can sustain ~98,000TPS with plain updates, or ~70,000 TPS with "equivalent" upserts.B-Tree index page heavyweight lock contention probably explains someof the difference between "UPSERT inserts" and "UPSERT updates". Recall that when we find a conflict (within _bt_checkunique()), itmust be conclusively committed and visible to new MVCC snapshots; weknow at that juncture that it's live. One of those two outcomes must be guaranteed, regardless of concurrent activity, which has been called \"the essential property of UPSERT\". You don't need a uniqueindex at all, and as I showed in my pgCon talk, there are raceconditions even for a trivial UPSERT operations in all major SQL MERGEimplementations. Why bother introducinga complicated distinction, if it's a distinction without a difference?I'd rather have a behavior that is consistent, easy to reason about,and easy to explain. And this process is known as upsert, which is the combination of insert or update command. 2. When using the UPDATEstatement, all of the rows in the table can be modified or just a subset may be updated using a condition. And so, the predicate is considered once, afterconclusively locking a conflict tuple. When we left off, Heikki continued to favor an approach that involvedspeculatively inserting heap tuples, and then deleting them in theevent of a conflict. Any expression using the table's columns, and/or columns of other tables mentioned in FROM, can be computed. You don't accept that value locks must be easily released in theevent of a conflict. Recall that we aren't quite dealing with MVCCsemantics here, since in READ COMMITTED mode we can lock aconclusively committed + visible tuple with *no* version visible toour command's MVCC snapshot. Also, some of the restrictions that I already mentioned- on updatable views, inheritance, and foreign tables - are probablyunnecessary. This tutorial will explain how to use Postgres to update from another table. Therefore, it seems worth considering thepossibility that the nbtree README's observations on the necessity ofholding a pin to interlock against VACUUM (for non-MVCC snapshots)apply. ON CONSTRAINT constraint_name – where the constraint name could be the name of … We can also choose to update instead of doing nothing: sql postgres=# insert into users values (uuid_generate_v4(), 'Lucie', 'Hawkins', 'Lucie-Jones@gmail.com') on conflict (email) do update set first_name = excluded.first_name, last_name = excluded.last_name; The Right Thing is far fromobvious, and there is very little to garner from other systems, sinceSQL MERGE promises essentially nothing about concurrency, both asspecified by the standard and in practice. INSERT has been augmented with a newclause, but that clause does not unreasonably fail to play nice withany other aspect of insertion. It is a discussion and guide to implementing CouchDB style conflict resolution with Postgres (central backend database) and PouchDB (frontend app user database).. I have (temporarily) hacked theoptimizer to prevent index-only scans, which are problematic here, byadding disable_cost when a query parse tree that uses the feature isseen. PostgreSQL › PostgreSQL - hackers. I thought, only the columns that I declared inside the ON CONFLICT()  parenthesis can be called in SET. Note that making mandatory (via syntax) merging on one particularunique index buys the implementation no useful leeway. transformStmt()/transformUpdateStmt() is called, and isinsulated from having to care about the feature as a special case).There are some restrictions on what this auxiliary update may do, butFWIW there are considerably fewer than those that the equivalent MySQLor SQLite feature imposes on their users. This is probably too paranoid, though: the fact that the upserter'stransaction is running ought to imply that GetOldestXmin() returns anXID sufficient to prevent this. In PostgreSQL 9.5, the ON CONFLICT clause was added to INSERT. Plus, there's the additional planning and parsingoverhead. The effect is similar to MySQL: INSERT INTO customers (id, first_name, last_name, email) VALUES (30797, 'hooopo1', 'wang', '[email protected]') ON CONFLICT(id) DO UPDATE SET first_name = EXCLUDED.first_name, last_name = EXCLUDED.last_name; Batch Upsert. In addition, stresstesting is an important part of my testing strategy. I've tried to break it up into pieces, but it isn't allthat suitable for representing as cumulative commits. Second, specify columns and their new values after SET keyword. I welcome new, interesting test cases.). We may or may not also actually proceedwith the update, depending on whether or not the user-specifiedspecial update predicate (if any) is satisfied. Previously, we have to use upsert or merge statement to do this kind of operation. That makes it impossible for the heap tuple slot to fail torelate to the tuple from the B-Tree, that is under consideration forlocking/updating. I havemade a concerted effort to break the patch in that way, and I'm nowrunning out of ideas. ON CONFLICT DO UPDATE updates the existing row that conflicts with the row proposed for insertion as its alternative action. I'm not sure how widely appreciated this pointis, but I believe that Heikki appreciates it. This can be revisited.). The per-tuple expression context of the auxiliary query/plan is usedwith EvalPlanQual() from within ExecLockUpdateTuple() (the new routinetasked with locking and updating on conflict). This happens to insulate ExecUpdate() from havingto care about "invisible tuples", which are now possible (although westill throw an error, just with a useful error message that phrasesthe problem in reference to this new feature). How this new approach works (Executor and Optimizer stuff)============================================. WHERE condition – update some fields in the table. In other words: I'm relying on the way VACUUM actually works toprevent premature garbage collection. In this article, we’ll take a closer look at the PostgreSQL UPSERT keyword and check out some examples of its use. On Thu, May 10, 2018 at 1:13 PM, tango ward. On an 8 core test server, I can sustain ~90,000 ordinary inserttransactions per second on an unlogged table defined as follows: create unlogged table foo( merge serial primary key, b int4, c text); In all cases pgbench uses 8 clients (1 per CPU core). This post continues to dive deeper into the topic. If you are using an earlier version, you will need a workaround to have the upsert feature. \"UPSERT\" is a DBMS feature that allows a DML statement's author to atomically either insert a row, or on the basis of the row already existing, UPDATE that existing row instead, while safely giving little to no further thought to concurrency. When we are inserting a new row into a particular table, the PostgreSQL will upgrade the row if it is already present, or else, it will add the new row. Pinning the heavyweight lock page's buffer iscertainly justified by the need for non-speculative inserters to see aflag that obligates them to acquire the heavyweight page lockthemselves (see comments in patch for more), but this other reason iskind of dubious. We’ve been talking about offline-first with Hasura and RxDB (essentially Postgres and PouchDB underneath).. Attached WIP patch extends the INSERT statement, adding a new ONCONFLICT {UPDATE | IGNORE} clause. Old versions ofthis patch used to sit on the B-Tree buffer pin to prevent concurrentdeletion only as long as value locks were held, but maybe it isn'tgood enough to sit on the pin until before we lock/update, as valuelocks are released: dropping the pin implies that the heap tuple canphysically go away, and in general the same TID may then containanything. Checking all columns is a) not. All of the following SQLqueries are valid with the patch applied: -- Nesting within wCTE:WITH t AS ( INSERT INTO z SELECT i, 'insert' FROM generate_series(0, 16) i ON CONFLICT UPDATE SET v = v || 'update' -- use ofoperators/functions in targetlist RETURNING * -- only projects inserted tuples, never updated tuples)SELECT * FROM t JOIN y ON t.k = y.a ORDER BY a, k; -- IGNORE variant:INSERT INTO upsert(key, val) VALUES(1, 'insert') ON CONFLICT IGNORE; -- predicate within UPDATE auxiliary statement (row is still lockedwhen the UPDATE predicate isn't satisfied):INSERT INTO upsert(key, val) VALUES(1, 'insert') ON CONFLICT UPDATEWHERE val != 'delete'; As with SQL MERGE (at least as implemented in other systems),subqueries may not appear within the UPDATE's targetlist, nor may theyappear within the special WHERE clause. Upsert (INSERT ON CONFLICT DO) is a new function of PostgreSQL 9.5. The patch has been committed , and will appear in PostgreSQL 9. You acceptthat value locks must be released and released easily in the event ofa conflict, but like Heikki you just don't like what I've done to getthere. Rather, its parent manages theprocess as the need arises. When performing inference, it consists of one or more index_column_name columns and/or index_expression expressions, and an optional index_predicate. This allows INSERT statements toperform UPSERT operations (if you want a more formal definition ofUPSERT, I refer you to my pgCon talk's slides [1], or the thread inwhich I delineated the differences between SQL MERGE and UPSERT [2]).The patch builds on previous work in this area, and incorporatesfeedback from Kevin and Andres. In general,at least with Postgres it's entirely possible that values rejecteddiffer from the values appearing in the VALUES() list, due to theeffects of before triggers. The first scenario is one in which weupdate despite our update's (or rather insert's) "predicate" not beingsatisfied (according to our MVCC snapshot). There is a newExecUpdate() call site within ExecLockUpdateTuple(). PostgreSQL added … When comparing updating with updating upserting, it's a similar story.100,000 tuples are pre-inserted in each case. update resolve the problem: the problem was that i declared two different mode for make unique email and username, for resolve this problem i delete unique near the collums and use only unique constraint "UX" for email and username. PostgreSQL added the ON CONFLICT target action clause to the INSERT statement to support the upsert feature. Granted, it is kind of bizarre that theauxiliary query may have a more complex plan than is necessary for ourpurposes, but it doesn't actually appear to be a problem when"rescanning" (Like a SELECT FOR UPDATE/FOR SHARE's node, we callEvalPlanQualSetTuple() directly). Compatibility INSERT conforms to the SQL standard, except that the RETURNING clause is a PostgreSQL extension, as is the ability to use WITH with INSERT, and the ability to specify an alternative action with ON CONFLICT. I think it makes sense to deal with it a bit later. In the PostgreSQL, the below query is used to upsert the table using the INSERT ON CONFLICT command: This design was made more complicated when theneed to *release* value locks became apparent (Heikki ended up makingsome changes to HeapTupleSatisfiesDirty(), as well as sketching adesign for what you might call a "super delete", where xmin can be setto InvalidTransactionId for speculatively-inserted heap tuples). Running the stress tests (with random delays inkey points in the code) for several days reveals no bugs. However, unlike with that SQLite feature, CONFLICT onlyrefers to a would-be duplicate violation, and not a violation of anyother kind of constraint. But this is aparticularly unsympathetic case, because I've deliberately exaggeratedthe effects of heavyweight lock contention on leaf pages by using aserial primary key. Anyway, the greater point here is that fundamentally, AFAICT Heikkiand I were in agreement. Upserts are comparedagainst "equivalent" inserts when we know we'll never update, andagainst "equivalent" updates when we know we'll never insert. So, for example, during parseanalysis, UPDATE transformation occurs in an ad-hoc fashion tightlydriven by the parent INSERT, but using the existing infrastructure(i.e. Having taken into account the experience of myself and Heikki, andall that is implied by taking that approach ***while avoidingunprincipled deadlocks***, you continue to believe that an approachbased on speculative heap insertion, or some alternative scheme isbetter than what I have done to the nbtree code here, or you otherwisedislike something about the proposed value locking scheme. It is convenient to be able to re-use infrastructure in such away as to more or less handle the UPDATE independently, driven by theINSERT, except for execution which is more directly handled by theINSERT (i.e. You may write the DML statementlike this: INSERT INTO upsert(key, val) VALUES(1, 'insert') ON CONFLICT WITHINupsert_pkey UPDATE SET val = 'update'; I think that there is a good chance that at least some people willwant to make this mandatory. It feels natural and appropriate to me that if the special UPDATE qualisn't satisfied, we still lock the tuple. ExecModifyTable() is never called with this specialauxiliary plan state passed directly. Reply | Threaded. Just forexample, the unprincipled deadlocks test case that illustrated theproblem with early "promise tuple" style approaches to value locking[6] involved only a single unique index. A day before yesterday, I got an email like, does it require to add a unique index on those columns which we require to be in ON CONFLICT clause? INSERT INTO upsert(key, val) VALUES(1, 'insert') ON CONFLICT UPDATESET val = 'update'; Essentially, the implementation has all stages of query processingtrack some auxiliary UPDATE state. [1] http://www.pgcon.org/2014/schedule/attachments/327_upsert_weird.pdf,("Goals for UPSERT in Postgres")[2] http://www.postgresql.org/message-id/CAM3SWZRP0c3g6+aJ=YYDGYAcTZg0xA8-1_FCVo5Xm7hrEL34kw@mail.gmail.com[3] https://sqlite.org/lang_conflict.html[4] http://www.postgresql.org/message-id/CAM3SWZQoArVQGMi=v-jk3sBjsPg+wdjeUkM_6L5TZG_i9pyGzQ@mail.gmail.com[5] http://www.postgresql.org/message-id/52B4AAF0.5090806@vmware.com[6] http://www.postgresql.org/message-id/CAM3SWZShbE29KpoD44cVc3vpZJGmDer6k_6FGHiSzeOZGmTFSQ@mail.gmail.com[7] http://www.postgresql.org/message-id/CAM3SWZRtV+xmRWLWq6c-x7czvwavFdwFi4St1zz4dDgFH4yN4g@mail.gmail.com-- Peter Geoghegan, Copyright © 1996-2020 The PostgreSQL Global Development Group, CAM3SWZTEODEJLz82LK4eF2HYX+qEKrbc8-Vtq3_-aOf6kRSfiA@mail.gmail.com, http://www.pgcon.org/2014/schedule/attachments/327_upsert_weird.pdf, http://www.postgresql.org/message-id/CAM3SWZRP0c3g6+aJ=YYDGYAcTZg0xA8-1_FCVo5Xm7hrEL34kw@mail.gmail.com, http://www.postgresql.org/message-id/CAM3SWZQoArVQGMi=v-jk3sBjsPg+wdjeUkM_6L5TZG_i9pyGzQ@mail.gmail.com, http://www.postgresql.org/message-id/52B4AAF0.5090806@vmware.com, http://www.postgresql.org/message-id/CAM3SWZShbE29KpoD44cVc3vpZJGmDer6k_6FGHiSzeOZGmTFSQ@mail.gmail.com, http://www.postgresql.org/message-id/CAM3SWZRtV+xmRWLWq6c-x7czvwavFdwFi4St1zz4dDgFH4yN4g@mail.gmail.com, 0001-Make-UPDATE-privileges-distinct-from-INSERT-privileg.patch, 0004-Internal-documentation-for-INSERT-.-ON-CONFLICT-UPDA.patch, 0003-Tests-for-INSERT-.-ON-CONFLICT-UPDATE-IGNORE.patch, 0002-Support-INSERT-.-ON-CONFLICT-UPDATE-IGNORE.patch, Re: INSERT ... 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