mirror of https://github.com/postgres/postgres
Tom Lane
19 years ago
parent
2fca2c05e7
commit
7b78474da3
@ -0,0 +1,631 @@ |
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/*-------------------------------------------------------------------------
|
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* |
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* rewriteheap.c |
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* Support functions to rewrite tables. |
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* |
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* These functions provide a facility to completely rewrite a heap, while |
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* preserving visibility information and update chains. |
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* |
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* INTERFACE |
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* |
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* The caller is responsible for creating the new heap, all catalog |
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* changes, supplying the tuples to be written to the new heap, and |
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* rebuilding indexes. The caller must hold AccessExclusiveLock on the |
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* target table, because we assume no one else is writing into it. |
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* |
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* To use the facility: |
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* |
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* begin_heap_rewrite |
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* while (fetch next tuple) |
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* { |
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* if (tuple is dead) |
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* rewrite_heap_dead_tuple |
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* else |
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* { |
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* // do any transformations here if required
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* rewrite_heap_tuple |
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* } |
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* } |
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* end_heap_rewrite |
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* |
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* The contents of the new relation shouldn't be relied on until after |
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* end_heap_rewrite is called. |
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* |
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* |
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* IMPLEMENTATION |
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* |
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* This would be a fairly trivial affair, except that we need to maintain |
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* the ctid chains that link versions of an updated tuple together. |
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* Since the newly stored tuples will have tids different from the original |
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* ones, if we just copied t_ctid fields to the new table the links would |
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* be wrong. When we are required to copy a (presumably recently-dead or |
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* delete-in-progress) tuple whose ctid doesn't point to itself, we have |
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* to substitute the correct ctid instead. |
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* |
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* For each ctid reference from A -> B, we might encounter either A first |
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* or B first. (Note that a tuple in the middle of a chain is both A and B |
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* of different pairs.) |
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* |
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* If we encounter A first, we'll store the tuple in the unresolved_tups |
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* hash table. When we later encounter B, we remove A from the hash table, |
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* fix the ctid to point to the new location of B, and insert both A and B |
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* to the new heap. |
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* |
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* If we encounter B first, we can insert B to the new heap right away. |
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* We then add an entry to the old_new_tid_map hash table showing B's |
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* original tid (in the old heap) and new tid (in the new heap). |
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* When we later encounter A, we get the new location of B from the table, |
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* and can write A immediately with the correct ctid. |
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* |
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* Entries in the hash tables can be removed as soon as the later tuple |
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* is encountered. That helps to keep the memory usage down. At the end, |
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* both tables are usually empty; we should have encountered both A and B |
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* of each pair. However, it's possible for A to be RECENTLY_DEAD and B |
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* entirely DEAD according to HeapTupleSatisfiesVacuum, because the test |
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* for deadness using OldestXmin is not exact. In such a case we might |
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* encounter B first, and skip it, and find A later. Then A would be added |
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* to unresolved_tups, and stay there until end of the rewrite. Since |
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* this case is very unusual, we don't worry about the memory usage. |
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* |
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* Using in-memory hash tables means that we use some memory for each live |
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* update chain in the table, from the time we find one end of the |
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* reference until we find the other end. That shouldn't be a problem in |
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* practice, but if you do something like an UPDATE without a where-clause |
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* on a large table, and then run CLUSTER in the same transaction, you |
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* could run out of memory. It doesn't seem worthwhile to add support for |
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* spill-to-disk, as there shouldn't be that many RECENTLY_DEAD tuples in a |
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* table under normal circumstances. Furthermore, in the typical scenario |
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* of CLUSTERing on an unchanging key column, we'll see all the versions |
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* of a given tuple together anyway, and so the peak memory usage is only |
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* proportional to the number of RECENTLY_DEAD versions of a single row, not |
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* in the whole table. Note that if we do fail halfway through a CLUSTER, |
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* the old table is still valid, so failure is not catastrophic. |
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* |
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* We can't use the normal heap_insert function to insert into the new |
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* heap, because heap_insert overwrites the visibility information. |
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* We use a special-purpose raw_heap_insert function instead, which |
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* is optimized for bulk inserting a lot of tuples, knowing that we have |
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* exclusive access to the heap. raw_heap_insert builds new pages in |
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* local storage. When a page is full, or at the end of the process, |
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* we insert it to WAL as a single record and then write it to disk |
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* directly through smgr. Note, however, that any data sent to the new |
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* heap's TOAST table will go through the normal bufmgr. |
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* |
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* |
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* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group |
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* Portions Copyright (c) 1994-5, Regents of the University of California |
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* |
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* IDENTIFICATION |
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* $PostgreSQL: pgsql/src/backend/access/heap/rewriteheap.c,v 1.1 2007/04/08 01:26:27 tgl Exp $ |
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* |
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*------------------------------------------------------------------------- |
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*/ |
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#include "postgres.h" |
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#include "access/heapam.h" |
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#include "access/rewriteheap.h" |
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#include "access/transam.h" |
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#include "access/tuptoaster.h" |
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#include "storage/smgr.h" |
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#include "utils/memutils.h" |
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/*
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* State associated with a rewrite operation. This is opaque to the user |
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* of the rewrite facility. |
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*/ |
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typedef struct RewriteStateData |
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{ |
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Relation rs_new_rel; /* destination heap */ |
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Page rs_buffer; /* page currently being built */ |
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BlockNumber rs_blockno; /* block where page will go */ |
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bool rs_buffer_valid; /* T if any tuples in buffer */ |
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bool rs_use_wal; /* must we WAL-log inserts? */ |
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TransactionId rs_oldest_xmin; /* oldest xmin used by caller to
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* determine tuple visibility */ |
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MemoryContext rs_cxt; /* for hash tables and entries and
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* tuples in them */ |
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HTAB *rs_unresolved_tups; /* unmatched A tuples */ |
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HTAB *rs_old_new_tid_map; /* unmatched B tuples */ |
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} RewriteStateData; |
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/*
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* The lookup keys for the hash tables are tuple TID and xmin (we must check |
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* both to avoid false matches from dead tuples). Beware that there is |
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* probably some padding space in this struct; it must be zeroed out for |
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* correct hashtable operation. |
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*/ |
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typedef struct |
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{ |
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TransactionId xmin; /* tuple xmin */ |
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ItemPointerData tid; /* tuple location in old heap */ |
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} TidHashKey; |
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/*
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* Entry structures for the hash tables |
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*/ |
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typedef struct |
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{ |
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TidHashKey key; /* expected xmin/old location of B tuple */ |
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ItemPointerData old_tid; /* A's location in the old heap */ |
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HeapTuple tuple; /* A's tuple contents */ |
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} UnresolvedTupData; |
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typedef UnresolvedTupData *UnresolvedTup; |
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typedef struct |
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{ |
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TidHashKey key; /* actual xmin/old location of B tuple */ |
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ItemPointerData new_tid; /* where we put it in the new heap */ |
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} OldToNewMappingData; |
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typedef OldToNewMappingData *OldToNewMapping; |
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/* prototypes for internal functions */ |
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static void raw_heap_insert(RewriteState state, HeapTuple tup); |
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/*
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* Begin a rewrite of a table |
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* |
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* new_heap new, locked heap relation to insert tuples to |
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* oldest_xmin xid used by the caller to determine which tuples are dead |
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* use_wal should the inserts to the new heap be WAL-logged? |
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* |
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* Returns an opaque RewriteState, allocated in current memory context, |
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* to be used in subsequent calls to the other functions. |
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*/ |
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RewriteState |
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begin_heap_rewrite(Relation new_heap, TransactionId oldest_xmin, |
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bool use_wal) |
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{ |
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RewriteState state; |
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MemoryContext rw_cxt; |
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MemoryContext old_cxt; |
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HASHCTL hash_ctl; |
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/*
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* To ease cleanup, make a separate context that will contain |
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* the RewriteState struct itself plus all subsidiary data. |
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*/ |
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rw_cxt = AllocSetContextCreate(CurrentMemoryContext, |
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"Table rewrite", |
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ALLOCSET_DEFAULT_MINSIZE, |
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ALLOCSET_DEFAULT_INITSIZE, |
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ALLOCSET_DEFAULT_MAXSIZE); |
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old_cxt = MemoryContextSwitchTo(rw_cxt); |
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/* Create and fill in the state struct */ |
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state = palloc0(sizeof(RewriteStateData)); |
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state->rs_new_rel = new_heap; |
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state->rs_buffer = (Page) palloc(BLCKSZ); |
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/* new_heap needn't be empty, just locked */ |
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state->rs_blockno = RelationGetNumberOfBlocks(new_heap); |
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/* Note: we assume RelationGetNumberOfBlocks did RelationOpenSmgr for us */ |
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state->rs_buffer_valid = false; |
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state->rs_use_wal = use_wal; |
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state->rs_oldest_xmin = oldest_xmin; |
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state->rs_cxt = rw_cxt; |
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/* Initialize hash tables used to track update chains */ |
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memset(&hash_ctl, 0, sizeof(hash_ctl)); |
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hash_ctl.keysize = sizeof(TidHashKey); |
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hash_ctl.entrysize = sizeof(UnresolvedTupData); |
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hash_ctl.hcxt = state->rs_cxt; |
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hash_ctl.hash = tag_hash; |
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state->rs_unresolved_tups = |
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hash_create("Rewrite / Unresolved ctids", |
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128, /* arbitrary initial size */ |
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&hash_ctl, |
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HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT); |
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hash_ctl.entrysize = sizeof(OldToNewMappingData); |
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state->rs_old_new_tid_map = |
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hash_create("Rewrite / Old to new tid map", |
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128, /* arbitrary initial size */ |
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&hash_ctl, |
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HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT); |
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MemoryContextSwitchTo(old_cxt); |
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return state; |
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} |
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/*
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* End a rewrite. |
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* |
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* state and any other resources are freed. |
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*/ |
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void |
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end_heap_rewrite(RewriteState state) |
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{ |
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HASH_SEQ_STATUS seq_status; |
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UnresolvedTup unresolved; |
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/*
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* Write any remaining tuples in the UnresolvedTups table. If we have |
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* any left, they should in fact be dead, but let's err on the safe side. |
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* |
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* XXX this really is a waste of code no? |
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*/ |
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hash_seq_init(&seq_status, state->rs_unresolved_tups); |
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while ((unresolved = hash_seq_search(&seq_status)) != NULL) |
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{ |
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ItemPointerSetInvalid(&unresolved->tuple->t_data->t_ctid); |
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raw_heap_insert(state, unresolved->tuple); |
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} |
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/* Write the last page, if any */ |
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if (state->rs_buffer_valid) |
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{ |
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if (state->rs_use_wal) |
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log_newpage(&state->rs_new_rel->rd_node, |
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state->rs_blockno, |
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state->rs_buffer); |
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smgrextend(state->rs_new_rel->rd_smgr, state->rs_blockno, |
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(char *) state->rs_buffer, true); |
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} |
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/*
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* If not WAL-logging, must fsync before commit. We use heap_sync |
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* to ensure that the toast table gets fsync'd too. |
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*/ |
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if (!state->rs_use_wal) |
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heap_sync(state->rs_new_rel); |
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/* Deleting the context frees everything */ |
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MemoryContextDelete(state->rs_cxt); |
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} |
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/*
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* Add a tuple to the new heap. |
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* |
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* Visibility information is copied from the original tuple. |
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* |
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* state opaque state as returned by begin_heap_rewrite |
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* old_tuple original tuple in the old heap |
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* new_tuple new, rewritten tuple to be inserted to new heap |
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*/ |
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void |
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rewrite_heap_tuple(RewriteState state, |
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HeapTuple old_tuple, HeapTuple new_tuple) |
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{ |
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MemoryContext old_cxt; |
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ItemPointerData old_tid; |
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TidHashKey hashkey; |
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bool found; |
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bool free_new; |
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old_cxt = MemoryContextSwitchTo(state->rs_cxt); |
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/*
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* Copy the original tuple's visibility information into new_tuple. |
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* |
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* XXX we might later need to copy some t_infomask2 bits, too? |
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*/ |
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memcpy(&new_tuple->t_data->t_choice.t_heap, |
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&old_tuple->t_data->t_choice.t_heap, |
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sizeof(HeapTupleFields)); |
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new_tuple->t_data->t_infomask &= ~HEAP_XACT_MASK; |
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new_tuple->t_data->t_infomask |= |
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old_tuple->t_data->t_infomask & HEAP_XACT_MASK; |
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/*
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* Invalid ctid means that ctid should point to the tuple itself. |
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* We'll override it later if the tuple is part of an update chain. |
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*/ |
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ItemPointerSetInvalid(&new_tuple->t_data->t_ctid); |
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/*
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* If the tuple has been updated, check the old-to-new mapping hash table. |
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*/ |
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if (!(old_tuple->t_data->t_infomask & (HEAP_XMAX_INVALID | |
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HEAP_IS_LOCKED)) && |
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!(ItemPointerEquals(&(old_tuple->t_self), |
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&(old_tuple->t_data->t_ctid)))) |
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{ |
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OldToNewMapping mapping; |
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memset(&hashkey, 0, sizeof(hashkey)); |
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hashkey.xmin = HeapTupleHeaderGetXmax(old_tuple->t_data); |
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hashkey.tid = old_tuple->t_data->t_ctid; |
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mapping = (OldToNewMapping) |
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hash_search(state->rs_old_new_tid_map, &hashkey, |
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HASH_FIND, NULL); |
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if (mapping != NULL) |
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{ |
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/*
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* We've already copied the tuple that t_ctid points to, so we |
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* can set the ctid of this tuple to point to the new location, |
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* and insert it right away. |
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*/ |
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new_tuple->t_data->t_ctid = mapping->new_tid; |
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/* We don't need the mapping entry anymore */ |
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hash_search(state->rs_old_new_tid_map, &hashkey, |
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HASH_REMOVE, &found); |
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Assert(found); |
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} |
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else |
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{ |
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/*
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* We haven't seen the tuple t_ctid points to yet. Stash this |
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* tuple into unresolved_tups to be written later. |
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*/ |
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UnresolvedTup unresolved; |
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unresolved = hash_search(state->rs_unresolved_tups, &hashkey, |
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HASH_ENTER, &found); |
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Assert(!found); |
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unresolved->old_tid = old_tuple->t_self; |
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unresolved->tuple = heap_copytuple(new_tuple); |
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/*
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* We can't do anything more now, since we don't know where the |
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* tuple will be written. |
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*/ |
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MemoryContextSwitchTo(old_cxt); |
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return; |
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} |
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} |
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/*
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* Now we will write the tuple, and then check to see if it is the |
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* B tuple in any new or known pair. When we resolve a known pair, |
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* we will be able to write that pair's A tuple, and then we have to |
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* check if it resolves some other pair. Hence, we need a loop here. |
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*/ |
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old_tid = old_tuple->t_self; |
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free_new = false; |
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for (;;) |
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{ |
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ItemPointerData new_tid; |
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/* Insert the tuple and find out where it's put in new_heap */ |
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raw_heap_insert(state, new_tuple); |
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new_tid = new_tuple->t_self; |
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/*
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* If the tuple is the updated version of a row, and the prior |
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* version wouldn't be DEAD yet, then we need to either resolve |
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* the prior version (if it's waiting in rs_unresolved_tups), |
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* or make an entry in rs_old_new_tid_map (so we can resolve it |
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* when we do see it). The previous tuple's xmax would equal this |
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* one's xmin, so it's RECENTLY_DEAD if and only if the xmin is |
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* not before OldestXmin. |
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*/ |
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if ((new_tuple->t_data->t_infomask & HEAP_UPDATED) && |
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!TransactionIdPrecedes(HeapTupleHeaderGetXmin(new_tuple->t_data), |
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state->rs_oldest_xmin)) |
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{ |
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/*
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* Okay, this is B in an update pair. See if we've seen A. |
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*/ |
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UnresolvedTup unresolved; |
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memset(&hashkey, 0, sizeof(hashkey)); |
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hashkey.xmin = HeapTupleHeaderGetXmin(new_tuple->t_data); |
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hashkey.tid = old_tid; |
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unresolved = hash_search(state->rs_unresolved_tups, &hashkey, |
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HASH_FIND, NULL); |
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if (unresolved != NULL) |
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{ |
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/*
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* We have seen and memorized the previous tuple already. |
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* Now that we know where we inserted the tuple its t_ctid |
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* points to, fix its t_ctid and insert it to the new heap. |
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*/ |
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if (free_new) |
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heap_freetuple(new_tuple); |
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new_tuple = unresolved->tuple; |
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free_new = true; |
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old_tid = unresolved->old_tid; |
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new_tuple->t_data->t_ctid = new_tid; |
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/*
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* We don't need the hash entry anymore, but don't free |
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* its tuple just yet. |
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*/ |
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hash_search(state->rs_unresolved_tups, &hashkey, |
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HASH_REMOVE, &found); |
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Assert(found); |
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/* loop back to insert the previous tuple in the chain */ |
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continue; |
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} |
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else |
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{ |
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/*
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* Remember the new tid of this tuple. We'll use it to set |
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* the ctid when we find the previous tuple in the chain. |
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*/ |
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OldToNewMapping mapping; |
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mapping = hash_search(state->rs_old_new_tid_map, &hashkey, |
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HASH_ENTER, &found); |
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Assert(!found); |
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mapping->new_tid = new_tid; |
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} |
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} |
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/* Done with this (chain of) tuples, for now */ |
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if (free_new) |
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heap_freetuple(new_tuple); |
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break; |
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} |
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MemoryContextSwitchTo(old_cxt); |
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} |
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|
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/*
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* Register a dead tuple with an ongoing rewrite. Dead tuples are not |
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* copied to the new table, but we still make note of them so that we |
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* can release some resources earlier. |
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*/ |
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void |
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rewrite_heap_dead_tuple(RewriteState state, HeapTuple old_tuple) |
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{ |
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/*
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* If we have already seen an earlier tuple in the update chain that |
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* points to this tuple, let's forget about that earlier tuple. It's |
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* in fact dead as well, our simple xmax < OldestXmin test in |
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* HeapTupleSatisfiesVacuum just wasn't enough to detect it. It |
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* happens when xmin of a tuple is greater than xmax, which sounds |
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* counter-intuitive but is perfectly valid. |
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* |
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* We don't bother to try to detect the situation the other way |
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* round, when we encounter the dead tuple first and then the |
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* recently dead one that points to it. If that happens, we'll |
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* have some unmatched entries in the UnresolvedTups hash table |
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* at the end. That can happen anyway, because a vacuum might |
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* have removed the dead tuple in the chain before us. |
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*/ |
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UnresolvedTup unresolved; |
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TidHashKey hashkey; |
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bool found; |
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|
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memset(&hashkey, 0, sizeof(hashkey)); |
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hashkey.xmin = HeapTupleHeaderGetXmin(old_tuple->t_data); |
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hashkey.tid = old_tuple->t_self; |
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unresolved = hash_search(state->rs_unresolved_tups, &hashkey, |
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HASH_FIND, NULL); |
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|
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if (unresolved != NULL) |
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{ |
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/* Need to free the contained tuple as well as the hashtable entry */ |
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heap_freetuple(unresolved->tuple); |
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hash_search(state->rs_unresolved_tups, &hashkey, |
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HASH_REMOVE, &found); |
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Assert(found); |
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} |
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} |
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|
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/*
|
||||
* Insert a tuple to the new relation. This has to track heap_insert |
||||
* and its subsidiary functions! |
||||
* |
||||
* t_self of the tuple is set to the new TID of the tuple. If t_ctid of the |
||||
* tuple is invalid on entry, it's replaced with the new TID as well (in |
||||
* the inserted data only, not in the caller's copy). |
||||
*/ |
||||
static void |
||||
raw_heap_insert(RewriteState state, HeapTuple tup) |
||||
{ |
||||
Page page = state->rs_buffer; |
||||
Size pageFreeSpace, saveFreeSpace; |
||||
Size len; |
||||
OffsetNumber newoff; |
||||
HeapTuple heaptup; |
||||
|
||||
/*
|
||||
* If the new tuple is too big for storage or contains already toasted |
||||
* out-of-line attributes from some other relation, invoke the toaster. |
||||
* |
||||
* Note: below this point, heaptup is the data we actually intend to store |
||||
* into the relation; tup is the caller's original untoasted data. |
||||
*/ |
||||
if (state->rs_new_rel->rd_rel->relkind == RELKIND_TOASTVALUE) |
||||
{ |
||||
/* toast table entries should never be recursively toasted */ |
||||
Assert(!HeapTupleHasExternal(tup)); |
||||
heaptup = tup; |
||||
} |
||||
else if (HeapTupleHasExternal(tup) || tup->t_len > TOAST_TUPLE_THRESHOLD) |
||||
heaptup = toast_insert_or_update(state->rs_new_rel, tup, NULL, |
||||
state->rs_use_wal, false); |
||||
else |
||||
heaptup = tup; |
||||
|
||||
len = MAXALIGN(heaptup->t_len); /* be conservative */ |
||||
|
||||
/*
|
||||
* If we're gonna fail for oversize tuple, do it right away |
||||
*/ |
||||
if (len > MaxHeapTupleSize) |
||||
ereport(ERROR, |
||||
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED), |
||||
errmsg("row is too big: size %lu, maximum size %lu", |
||||
(unsigned long) len, |
||||
(unsigned long) MaxHeapTupleSize))); |
||||
|
||||
/* Compute desired extra freespace due to fillfactor option */ |
||||
saveFreeSpace = RelationGetTargetPageFreeSpace(state->rs_new_rel, |
||||
HEAP_DEFAULT_FILLFACTOR); |
||||
|
||||
/* Now we can check to see if there's enough free space already. */ |
||||
if (state->rs_buffer_valid) |
||||
{ |
||||
pageFreeSpace = PageGetFreeSpace(page); |
||||
|
||||
if (len + saveFreeSpace > pageFreeSpace) |
||||
{ |
||||
/* Doesn't fit, so write out the existing page */ |
||||
|
||||
/* XLOG stuff */ |
||||
if (state->rs_use_wal) |
||||
log_newpage(&state->rs_new_rel->rd_node, |
||||
state->rs_blockno, |
||||
page); |
||||
|
||||
/*
|
||||
* Now write the page. We say isTemp = true even if it's not a |
||||
* temp table, because there's no need for smgr to schedule an |
||||
* fsync for this write; we'll do it ourselves before committing. |
||||
*/ |
||||
smgrextend(state->rs_new_rel->rd_smgr, state->rs_blockno, |
||||
(char *) page, true); |
||||
|
||||
state->rs_blockno++; |
||||
state->rs_buffer_valid = false; |
||||
} |
||||
} |
||||
|
||||
if (!state->rs_buffer_valid) |
||||
{ |
||||
/* Initialize a new empty page */ |
||||
PageInit(page, BLCKSZ, 0); |
||||
state->rs_buffer_valid = true; |
||||
} |
||||
|
||||
/* And now we can insert the tuple into the page */ |
||||
newoff = PageAddItem(page, (Item) heaptup->t_data, len, |
||||
InvalidOffsetNumber, LP_USED); |
||||
if (newoff == InvalidOffsetNumber) |
||||
elog(ERROR, "failed to add tuple"); |
||||
|
||||
/* Update caller's t_self to the actual position where it was stored */ |
||||
ItemPointerSet(&(tup->t_self), state->rs_blockno, newoff); |
||||
|
||||
/*
|
||||
* Insert the correct position into CTID of the stored tuple, too, |
||||
* if the caller didn't supply a valid CTID. |
||||
*/ |
||||
if(!ItemPointerIsValid(&tup->t_data->t_ctid)) |
||||
{ |
||||
ItemId newitemid; |
||||
HeapTupleHeader onpage_tup; |
||||
|
||||
newitemid = PageGetItemId(page, newoff); |
||||
onpage_tup = (HeapTupleHeader) PageGetItem(page, newitemid); |
||||
|
||||
onpage_tup->t_ctid = tup->t_self; |
||||
} |
||||
|
||||
/* If heaptup is a private copy, release it. */ |
||||
if (heaptup != tup) |
||||
heap_freetuple(heaptup); |
||||
} |
||||
@ -0,0 +1,29 @@ |
||||
/*-------------------------------------------------------------------------
|
||||
* |
||||
* rewriteheap.h |
||||
* Declarations for heap rewrite support functions |
||||
* |
||||
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group |
||||
* Portions Copyright (c) 1994-5, Regents of the University of California |
||||
* |
||||
* $PostgreSQL: pgsql/src/include/access/rewriteheap.h,v 1.1 2007/04/08 01:26:33 tgl Exp $ |
||||
* |
||||
*------------------------------------------------------------------------- |
||||
*/ |
||||
#ifndef REWRITE_HEAP_H |
||||
#define REWRITE_HEAP_H |
||||
|
||||
#include "access/htup.h" |
||||
#include "utils/rel.h" |
||||
|
||||
/* struct definition is private to rewriteheap.c */ |
||||
typedef struct RewriteStateData *RewriteState; |
||||
|
||||
extern RewriteState begin_heap_rewrite(Relation NewHeap, |
||||
TransactionId OldestXmin, bool use_wal); |
||||
extern void end_heap_rewrite(RewriteState state); |
||||
extern void rewrite_heap_tuple(RewriteState state, HeapTuple oldTuple, |
||||
HeapTuple newTuple); |
||||
extern void rewrite_heap_dead_tuple(RewriteState state, HeapTuple oldTuple); |
||||
|
||||
#endif /* REWRITE_HEAP_H */ |
||||
Loading…
Reference in new issue