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Re-think guts of DROP INDEX CONCURRENTLY.

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Concurrent behaviour was flawed when using
a two-step process, so add an additional
phase of processing to ensure concurrency
for both SELECTs and INSERT/UPDATE/DELETEs.

Backpatch to 9.2

Andres Freund, tweaked by me
This commit is contained in:
Simon Riggs 2012-10-18 18:58:30 +01:00
parent 72a4231f0c
commit 2f0e480d02
1 changed files with 90 additions and 14 deletions
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104
src/backend/catalog/index.c
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@ -1316,6 +1316,10 @@ index_drop(Oid indexId, bool concurrent)
* table lock strong enough to prevent all queries on the table from
* proceeding until we commit and send out a shared-cache-inval notice
* that will make them update their index lists.
*
* In the concurrent case we make sure that nobody can be looking at the
* indexes by dropping the index in multiple steps, so we don't need a full
* AccessExclusiveLock yet.
*/
heapId = IndexGetRelation(indexId, false);
if (concurrent)
@ -1336,7 +1340,19 @@ index_drop(Oid indexId, bool concurrent)
/*
* Drop Index concurrently is similar in many ways to creating an index
* concurrently, so some actions are similar to DefineIndex()
* concurrently, so some actions are similar to DefineIndex() just in the
* reverse order.
*
* First we unset indisvalid so queries starting afterwards don't use the
* index to answer queries anymore. We have to keep indisready = true
* so transactions that are still scanning the index can continue to
* see valid index contents. E.g. when they are using READ COMMITTED mode,
* and another transactions that started later commits makes changes and
* commits, they need to see those new tuples in the index.
*
* After all transactions that could possibly have used it for queries
* ended we can unset indisready and wait till nobody could be updating it
* anymore.
*/
if (concurrent)
{
@ -1355,21 +1371,21 @@ index_drop(Oid indexId, bool concurrent)
elog(ERROR, "cache lookup failed for index %u", indexId);
indexForm = (Form_pg_index) GETSTRUCT(tuple);
indexForm->indisvalid = false; /* make unusable for queries */
indexForm->indisready = false; /* make invisible to changes */
/*
* If indisready == true we leave it set so the index still gets
* maintained by pre-existing transactions. We only need to ensure
* that indisvalid is false.
*/
if (indexForm->indisvalid)
{
indexForm->indisvalid = false; /* make unusable for new queries */
simple_heap_update(indexRelation, &tuple->t_self, tuple);
CatalogUpdateIndexes(indexRelation, tuple);
simple_heap_update(indexRelation, &tuple->t_self, tuple);
CatalogUpdateIndexes(indexRelation, tuple);
}
heap_close(indexRelation, RowExclusiveLock);
/*
* Invalidate the relcache for the table, so that after this
* transaction we will refresh the index list. Forgetting just the
* index is not enough.
*/
CacheInvalidateRelcache(userHeapRelation);
/* save lockrelid and locktag for below, then close but keep locks */
heaprelid = userHeapRelation->rd_lockInfo.lockRelId;
SET_LOCKTAG_RELATION(heaplocktag, heaprelid.dbId, heaprelid.relId);
@ -1381,8 +1397,8 @@ index_drop(Oid indexId, bool concurrent)
/*
* For a concurrent drop, it's important to make the catalog entries
* visible to other transactions before we drop the index. The index
* will be marked not indisvalid, so that no one else tries to either
* insert into it or use it for queries.
* will be marked not indisvalid, so that no one else tries to use it
* for queries.
*
* We must commit our current transaction so that the index update
* becomes visible; then start another. Note that all the data
@ -1428,6 +1444,66 @@ index_drop(Oid indexId, bool concurrent)
old_lockholders++;
}
/*
* Now we are sure that nobody uses the index for queries, they just
* might have it opened for updating it. So now we can unset
* indisready and wait till nobody could update the index anymore.
*/
indexRelation = heap_open(IndexRelationId, RowExclusiveLock);
userHeapRelation = heap_open(heapId, ShareUpdateExclusiveLock);
userIndexRelation = index_open(indexId, ShareUpdateExclusiveLock);
tuple = SearchSysCacheCopy1(INDEXRELID,
ObjectIdGetDatum(indexId));
if (!HeapTupleIsValid(tuple))
elog(ERROR, "cache lookup failed for index %u", indexId);
indexForm = (Form_pg_index) GETSTRUCT(tuple);
Assert(indexForm->indisvalid == false);
if (indexForm->indisready)
{
indexForm->indisready = false; /* don't update index anymore */
simple_heap_update(indexRelation, &tuple->t_self, tuple);
CatalogUpdateIndexes(indexRelation, tuple);
}
heap_close(indexRelation, RowExclusiveLock);
/*
* Close the relations again, though still holding session lock.
*/
heap_close(userHeapRelation, NoLock);
index_close(userIndexRelation, NoLock);
/*
* Invalidate the relcache for the table, so that after this
* transaction we will refresh the index list. Forgetting just the
* index is not enough.
*/
CacheInvalidateRelcache(userHeapRelation);
/*
* Just as with indisvalid = false we need to make sure indisready
* is false is visible for everyone.
*/
CommitTransactionCommand();
StartTransactionCommand();
/*
* Wait till everyone that saw indisready = true finished so we can
* finally really remove the index. The logic here is the same as
* above.
*/
old_lockholders = GetLockConflicts(&heaplocktag, AccessExclusiveLock);
while (VirtualTransactionIdIsValid(*old_lockholders))
{
VirtualXactLock(*old_lockholders, true);
old_lockholders++;
}
/*
* Re-open relations to allow us to complete our actions.
*