When possible, avoid taking wal file read-lock 0 in sqlite3_snapshot_get().
FossilOrigin-Name: 34b6ac3d76dbc6819778ec2a0f81cbcdcc0cd1a6303381d97f1c479e4ecdd132
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dan
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C In\sthe\sCLI,\sfor\scolumnar\soutput\sformats,\stry\sto\saccount\sfor\sthe\spresence\sof\nzero-width\sand\sdouble-width\scharacters\sin\sthe\soutput\sand\sadjust\scolumn\swidths\naccordingly.
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D 2024-09-25T09:39:11.501
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C When\spossible,\savoid\staking\swal\sfile\sread-lock\s0\sin\ssqlite3_snapshot_get().
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D 2024-09-26T18:02:17.495
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F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
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F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
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F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
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@ -730,7 +730,7 @@ F src/insert.c f8d1a0f8ee258411009c6b7f2d93170e351bd19f5ad89d57e1180644297cbe70
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F src/json.c 68a98c020c22127f2d65f08855f7fc7460ff352a6ce0b543d8931dde83319c22
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F src/legacy.c d7874bc885906868cd51e6c2156698f2754f02d9eee1bae2d687323c3ca8e5aa
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F src/loadext.c 7432c944ff197046d67a1207790a1b13eec4548c85a9457eb0896bb3641dfb36
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F src/main.c 4db6e3bde55ba0b24ccc83600c2b6ea11429f61ce7b3a2e7e3b42e1b45366c3e
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F src/main.c 3bb768eeeee1cceaed391327362b8be8b5ce61a12fe24d5b555ce9c6b4a883de
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F src/malloc.c 410e570b30c26cc36e3372577df50f7a96ee3eed5b2b161c6b6b48773c650c5e
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F src/mem0.c 6a55ebe57c46ca1a7d98da93aaa07f99f1059645
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F src/mem1.c 3bb59158c38e05f6270e761a9f435bf19827a264c13d1631c58b84bdc96d73b2
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@ -849,7 +849,7 @@ F src/vdbetrace.c fe0bc29ebd4e02c8bc5c1945f1d2e6be5927ec12c06d89b03ef2a4def34bf8
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F src/vdbevtab.c fc46b9cbd759dc013f0b3724549cc0d71379183c667df3a5988f7e2f1bd485f3
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F src/vtab.c 316cd48e9320660db3047cd306cd056e4361180cebb4d0f10a39244e10c11422
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F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
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F src/wal.c ef68130ba330ee18c1cb22da36a881c82e3a3b109badbdc6a9b9acaf788a6688
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F src/wal.c a0d42bfdef935e1389737152394d08e59e7c48697f40a9fc2e0552cb19dc731f
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F src/wal.h ba252daaa94f889f4b2c17c027e823d9be47ce39da1d3799886bbd51f0490452
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F src/walker.c d5006d6b005e4ea7302ad390957a8d41ed83faa177e412f89bc5600a7462a014
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F src/where.c 461d41017d900d4248a268df96d2d30506c4dcc2257f4167c4f46072003ce2cf
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@ -1647,7 +1647,7 @@ F test/skipscan5.test 0672103fd2c8f96bd114133f356192b35ece45c794fe3677e1d9e5e310
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F test/skipscan6.test bddbb35dd335e2d21b7791a61e3b2e1f3255dc307ce80aa6fe19cc298e6feb13
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F test/snapshot.test a504f2e7009f512ef66c719f0ea1c55a556bdaf1e1312c80a04d46fc1a3e9632
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F test/snapshot2.test 8d6ff5dd9cc503f6e12d408a30409c3f9c653507b24408d9cd7195931c89bc54
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F test/snapshot3.test 8744313270c55f6e18574283553d3c5c5fe4c5970585663613a0e75c151e599b
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F test/snapshot3.test 41350216abc6c7da37113ad462259c070786e5ad70bdc8709daaed148b1b3a2c
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F test/snapshot4.test d4e9347ef2fcabc491fc893506c7bbaf334da3be111d6eb4f3a97cc623b78322
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F test/snapshot_fault.test 129234ceb9b26a0e1000e8563a16e790f5c1412354e70749cbd78c3d5d07d60a
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F test/snapshot_up.test 77dc7853bfb2b4fa249f76e1714cfa1e596826165d9ef22c06ac3a0b7b778d9a
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@ -2213,9 +2213,11 @@ F vsixtest/vsixtest.tcl 6195aba1f12a5e10efc2b8c0009532167be5e301abe5b31385638080
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F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
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F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
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F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
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P 42bb941584a1ac922ee6b0b6ecadce71c9259555563cf49913a6f820f3f9b887 b217e3004b58af0e777726bdd652b999ad41815261299ef4ce8f8d2f6b0afe8d
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R 5fcf6775e686fdd76943c66cce860cb0
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T +closed b217e3004b58af0e777726bdd652b999ad41815261299ef4ce8f8d2f6b0afe8d
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U drh
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Z af457fc67e3efab459ef7260d9a5da46
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P 9592b9ba3ad7a842cdd4c4010da278485a6fdec7e811bda01ebe640162a8c3b6
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R 8553e4183ac33940fe95918021cfe535
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T *branch * snapshot_get-locking
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T *sym-snapshot_get-locking *
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T -sym-trunk *
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U dan
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Z 2b5e37766517d26ed8f4d4495c7d929b
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# Remove this line to create a well-formed Fossil manifest.
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@ -1 +1 @@
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9592b9ba3ad7a842cdd4c4010da278485a6fdec7e811bda01ebe640162a8c3b6
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34b6ac3d76dbc6819778ec2a0f81cbcdcc0cd1a6303381d97f1c479e4ecdd132
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@ -4963,7 +4963,11 @@ int sqlite3_snapshot_get(
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if( iDb==0 || iDb>1 ){
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Btree *pBt = db->aDb[iDb].pBt;
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if( SQLITE_TXN_WRITE!=sqlite3BtreeTxnState(pBt) ){
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Pager *pPager = sqlite3BtreePager(pBt);
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i64 dummy = 0;
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sqlite3PagerSnapshotOpen(pPager, (sqlite3_snapshot*)&dummy);
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rc = sqlite3BtreeBeginTrans(pBt, 0, 0);
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sqlite3PagerSnapshotOpen(pPager, 0);
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if( rc==SQLITE_OK ){
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rc = sqlite3PagerSnapshotGet(sqlite3BtreePager(pBt), ppSnapshot);
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}
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16
src/wal.c
16
src/wal.c
@ -541,6 +541,7 @@ struct Wal {
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#endif
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#ifdef SQLITE_ENABLE_SNAPSHOT
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WalIndexHdr *pSnapshot; /* Start transaction here if not NULL */
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int bGetSnapshot; /* Transaction opened for sqlite3_get_snapshot() */
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#endif
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#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
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sqlite3 *db;
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@ -3097,7 +3098,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int *pCnt){
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SEH_INJECT_FAULT;
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if( !useWal && AtomicLoad(&pInfo->nBackfill)==pWal->hdr.mxFrame
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#ifdef SQLITE_ENABLE_SNAPSHOT
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&& (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0)
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&& ((pWal->bGetSnapshot==0 && pWal->pSnapshot==0) || pWal->hdr.mxFrame==0)
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#endif
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){
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/* The WAL has been completely backfilled (or it is empty).
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@ -4497,7 +4498,20 @@ void sqlite3WalSnapshotOpen(
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Wal *pWal,
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sqlite3_snapshot *pSnapshot
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){
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if( pSnapshot && ((WalIndexHdr*)pSnapshot)->iVersion==0 ){
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/* iVersion==0 means that this is a call to sqlite3_snapshot_get(). In
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** this case set the bGetSnapshot flag so that if the call to
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** sqlite3_snapshot_get() is about to read transaction on this wal
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** file, it does not take read-lock 0 if the wal file has been completely
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** checkpointed. Taking read-lock 0 would work, but then it would be
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** possible for a subsequent writer to destroy the snapshot even while
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** this connection is holding its read-transaction open. This is contrary
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** to user expectations, so we avoid it by not taking read-lock 0. */
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pWal->bGetSnapshot = 1;
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}else{
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pWal->pSnapshot = (WalIndexHdr*)pSnapshot;
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pWal->bGetSnapshot = 0;
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}
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}
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/*
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@ -96,4 +96,43 @@ do_test 1.8 {
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list [catch { sqlite3_snapshot_open_blob db3 main $snap } msg] $msg
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} {1 SQLITE_ERROR_SNAPSHOT}
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#-------------------------------------------------------------------------
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reset_db
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do_execsql_test 2.0 {
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PRAGMA journal_mode = wal;
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CREATE TABLE t1(a, b);
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INSERT INTO t1 VALUES(1, 2);
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INSERT INTO t1 VALUES(3, 4);
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} {wal}
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sqlite3 db2 test.db
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sqlite3 db3 test.db
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do_execsql_test -db db2 2.0.1 {
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SELECT * FROM t1
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} {1 2 3 4}
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do_execsql_test -db db3 2.0.2 {
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SELECT * FROM t1
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} {1 2 3 4}
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do_execsql_test -db db2 2.2 {
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PRAGMA wal_checkpoint;
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} {0 4 4}
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do_test 2.1 {
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db eval { BEGIN }
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set snap [sqlite3_snapshot_get db main]
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set {} {}
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} {}
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do_execsql_test -db db2 2.3 {
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INSERT INTO t1 VALUES(5, 6);
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} {}
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do_test 2.2 {
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execsql { BEGIN } db3
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sqlite3_snapshot_open db3 main $snap
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} {}
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sqlite3_snapshot_free $snap
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finish_test
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