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MDEV-27746 Wrong comparision of BLOB's empty preffix with non-preffixed BLOB causes rows count mismatch for clustered and secondary indexes during non-locking read

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row_sel_sec_rec_is_for_clust_rec() treats empty BLOB prefix field in
secondary index as a field equal to any external BLOB field in clustered
index. Row_sel_get_clust_rec_for_mysql::operator() doesn't zerro out
clustered record pointer in row_search_mvcc(), and row_search_mvcc()
thinks that delete-marked secondary index record has visible for
"CHECK TABLE"'s read view old-versioned clustered index record, and
row_scan_index_for_mysql() counts it as a row.

The fix is to execute row_sel_sec_rec_is_for_blob() in
row_sel_sec_rec_is_for_clust_rec() if clustered field contains BLOB's
reference.
This commit is contained in:
Vlad Lesin
2022-02-09 16:50:28 +03:00
parent 3a52569499
commit 3b10e8f80c
3 changed files with 52 additions and 1 deletions
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19
mysql-test/suite/innodb/r/blob_cmp_empty.result Normal file
View File

@ -0,0 +1,19 @@
connect prevent_purge,localhost,root,,;
start transaction with consistent snapshot;
connection default;
SET @fill_amount = (@@innodb_page_size / 2 ) + 1;
CREATE TABLE t1 (col_text TEXT NOT NULL, KEY (col_text(9))) ENGINE=InnoDB;
INSERT INTO t1 (col_text) VALUES (REPEAT('x', @fill_amount));
UPDATE t1 SET col_text='';
UPDATE t1 SET col_text=REPEAT('y', @fill_amount);
connect con1,localhost,root,,;
SET @fill_amount = (@@innodb_page_size / 2 ) + 1;
BEGIN;
INSERT INTO t1 (col_text) VALUES (REPEAT('z', @fill_amount));
connection default;
CHECK TABLE t1;
Table Op Msg_type Msg_text
test.t1 check status OK
disconnect con1;
disconnect prevent_purge;
DROP TABLE t1;

26
mysql-test/suite/innodb/t/blob_cmp_empty.test Normal file
View File

@ -0,0 +1,26 @@
--source include/innodb_row_format.inc
--source include/count_sessions.inc
--connect(prevent_purge,localhost,root,,)
start transaction with consistent snapshot;
--connection default
SET @fill_amount = (@@innodb_page_size / 2 ) + 1;
CREATE TABLE t1 (col_text TEXT NOT NULL, KEY (col_text(9))) ENGINE=InnoDB;
INSERT INTO t1 (col_text) VALUES (REPEAT('x', @fill_amount));
UPDATE t1 SET col_text='';
UPDATE t1 SET col_text=REPEAT('y', @fill_amount);
--connect(con1,localhost,root,,)
SET @fill_amount = (@@innodb_page_size / 2 ) + 1;
BEGIN;
INSERT INTO t1 (col_text) VALUES (REPEAT('z', @fill_amount));
--connection default
# If the bug is not fixed, CHECK TABLE will complain about wrong secondary index
# rows count
CHECK TABLE t1;
--disconnect con1
--disconnect prevent_purge
DROP TABLE t1;
--source include/wait_until_count_sessions.inc

8
storage/innobase/row/row0sel.cc
View File

@ -352,11 +352,16 @@ row_sel_sec_rec_is_for_clust_rec(
} }
len = clust_len; len = clust_len;
ulint prefix_len = ifield->prefix_len;
if (rec_offs_nth_extern(clust_offs, clust_pos)) { if (rec_offs_nth_extern(clust_offs, clust_pos)) {
/* BLOB can contain prefix. */
len -= BTR_EXTERN_FIELD_REF_SIZE; len -= BTR_EXTERN_FIELD_REF_SIZE;
if (!len) {
goto compare_blobs;
}
} }
if (ulint prefix_len = ifield->prefix_len) { if (prefix_len) {
len = dtype_get_at_most_n_mbchars( len = dtype_get_at_most_n_mbchars(
col->prtype, col->mbminlen, col->prtype, col->mbminlen,
col->mbmaxlen, prefix_len, len, col->mbmaxlen, prefix_len, len,
@ -369,6 +374,7 @@ row_sel_sec_rec_is_for_clust_rec(
check_for_blob: check_for_blob:
if (rec_offs_nth_extern(clust_offs, if (rec_offs_nth_extern(clust_offs,
clust_pos)) { clust_pos)) {
compare_blobs:
if (!row_sel_sec_rec_is_for_blob( if (!row_sel_sec_rec_is_for_blob(
col->mtype, col->prtype, col->mtype, col->prtype,
col->mbminlen, col->mbminlen,