diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/main.c | 4 | ||||
| -rw-r--r-- | src/sqlite.h.in | 8 | ||||
| -rw-r--r-- | src/wal.c | 18 |
3 files changed, 28 insertions, 2 deletions
diff --git a/src/main.c b/src/main.c index bd0cbc731..bfbabcbec 100644 --- a/src/main.c +++ b/src/main.c @@ -4968,7 +4968,11 @@ int sqlite3_snapshot_get( if( iDb==0 || iDb>1 ){ Btree *pBt = db->aDb[iDb].pBt; if( SQLITE_TXN_WRITE!=sqlite3BtreeTxnState(pBt) ){ + Pager *pPager = sqlite3BtreePager(pBt); + i64 dummy = 0; + sqlite3PagerSnapshotOpen(pPager, (sqlite3_snapshot*)&dummy); rc = sqlite3BtreeBeginTrans(pBt, 0, 0); + sqlite3PagerSnapshotOpen(pPager, 0); if( rc==SQLITE_OK ){ rc = sqlite3PagerSnapshotGet(sqlite3BtreePager(pBt), ppSnapshot); } diff --git a/src/sqlite.h.in b/src/sqlite.h.in index 72190beec..a87ea4591 100644 --- a/src/sqlite.h.in +++ b/src/sqlite.h.in @@ -10543,6 +10543,14 @@ typedef struct sqlite3_snapshot { ** If there is not already a read-transaction open on schema S when ** this function is called, one is opened automatically. ** +** If a read-transaction is opened by this function, then it is guaranteed +** that the returned snapshot object may not be invalidated by a database +** writer or checkpointer until after the read-transaction is closed. This +** is not guaranteed if a read-transaction is already open when this +** function is called. In that case, any subsequent write or checkpoint +** operation on the database may invalidate the returned snapshot handle, +** even while the read-transaction remains open. +** ** The following must be true for this function to succeed. If any of ** the following statements are false when sqlite3_snapshot_get() is ** called, SQLITE_ERROR is returned. The final value of *P is undefined @@ -541,6 +541,7 @@ struct Wal { #endif #ifdef SQLITE_ENABLE_SNAPSHOT WalIndexHdr *pSnapshot; /* Start transaction here if not NULL */ + int bGetSnapshot; /* Transaction opened for sqlite3_get_snapshot() */ #endif #ifdef SQLITE_ENABLE_SETLK_TIMEOUT sqlite3 *db; @@ -3097,7 +3098,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int *pCnt){ SEH_INJECT_FAULT; if( !useWal && AtomicLoad(&pInfo->nBackfill)==pWal->hdr.mxFrame #ifdef SQLITE_ENABLE_SNAPSHOT - && (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0) + && ((pWal->bGetSnapshot==0 && pWal->pSnapshot==0) || pWal->hdr.mxFrame==0) #endif ){ /* The WAL has been completely backfilled (or it is empty). @@ -4497,7 +4498,20 @@ void sqlite3WalSnapshotOpen( Wal *pWal, sqlite3_snapshot *pSnapshot ){ - pWal->pSnapshot = (WalIndexHdr*)pSnapshot; + if( pSnapshot && ((WalIndexHdr*)pSnapshot)->iVersion==0 ){ + /* iVersion==0 means that this is a call to sqlite3_snapshot_get(). In + ** this case set the bGetSnapshot flag so that if the call to + ** sqlite3_snapshot_get() is about to read transaction on this wal + ** file, it does not take read-lock 0 if the wal file has been completely + ** checkpointed. Taking read-lock 0 would work, but then it would be + ** possible for a subsequent writer to destroy the snapshot even while + ** this connection is holding its read-transaction open. This is contrary + ** to user expectations, so we avoid it by not taking read-lock 0. */ + pWal->bGetSnapshot = 1; + }else{ + pWal->pSnapshot = (WalIndexHdr*)pSnapshot; + pWal->bGetSnapshot = 0; + } } /* |