mirror/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-02-01 03:21:53 +01:00
Code Issues Projects Releases Packages Wiki Activity Actions

Correct some comments that were added in the fix of Bug #54358

Browse source 
(READ UNCOMMITTED access failure of off-page DYNAMIC or COMPRESSED columns).

Records that lack incompletely written externally stored columns may
be accessed by READ UNCOMMITTED transaction even without involving a
crash during an INSERT or UPDATE operation. I verified this as follows.

(1) added a delay after the mini-transaction for writing the clustered
index 'stub' record was committed (patch attached)
(2) started mysqld in gdb, setting breakpoints to the where the
assertions about READ UNCOMMITTED were added in the bug fix
(3) invoked ibtest3 --create-options=key_block_size=2
to create BLOBs in a COMPRESSED table
(4) invoked the following:
yes 'set transaction isolation level read uncommitted;
checksum table blobt3;select sleep(1);'|mysql -uroot test
(5) noted that one of the breakpoints was triggered
(return(NULL) in btr_rec_copy_externally_stored_field())

=== modified file 'storage/innodb_plugin/row/row0ins.c'
--- storage/innodb_plugin/row/row0ins.c	2010-06-30 08:17:25 +0000
+++ storage/innodb_plugin/row/row0ins.c	2010-06-30 08:17:25 +0000
@@ -2120,6 +2120,7 @@ function_exit:
 		rec_t*	rec;
 		ulint*	offsets;
 		mtr_start(&mtr);
+		os_thread_sleep(5000000);
 
 		btr_cur_search_to_nth_level(index, 0, entry, PAGE_CUR_LE,
 					    BTR_MODIFY_TREE, &cursor, 0,

=== modified file 'storage/innodb_plugin/row/row0upd.c'
--- storage/innodb_plugin/row/row0upd.c	2010-06-30 08:11:55 +0000
+++ storage/innodb_plugin/row/row0upd.c	2010-06-30 08:11:55 +0000
@@ -1763,6 +1763,7 @@ row_upd_clust_rec(
 		rec_offs_init(offsets_);
 
 		mtr_start(mtr);
+		os_thread_sleep(5000000);
 
 		ut_a(btr_pcur_restore_position(BTR_MODIFY_TREE, pcur, mtr));
 		rec = btr_cur_get_rec(btr_cur);
This commit is contained in:
Marko Mäkelä 2010-06-30 12:31:49 +03:00
parent 5a25f40815
commit 5754382c31
2 changed files with 19 additions and 48 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

14
storage/innodb_plugin/btr/btr0cur.c
View file

@ -4849,20 +4849,10 @@ btr_rec_copy_externally_stored_field(
if (UNIV_UNLIKELY
(!memcmp(data + local_len - BTR_EXTERN_FIELD_REF_SIZE,
field_ref_zero, BTR_EXTERN_FIELD_REF_SIZE))) {
/* The externally stored field was not written
yet. This is only a valid condition when the server
crashed after the time a record stub was freshly
inserted but before all its columns were written. This
record should only be seen by
/* The externally stored field was not written yet.
This record should only be seen by
recv_recovery_rollback_active() or any
TRX_ISO_READ_UNCOMMITTED transactions. */
/* TODO: assert that there is an owner_trx with
owner_trx->id == DB_TRX_ID and owner_trx->is_recovered */
/* TODO: assert that for the current transaction trx,
either (trx == owner_trx && trx_is_recv(trx)) or
trx->isolation_level == TRX_ISO_READ_UNCOMMITTED. */
return(NULL);
}

53
storage/innodb_plugin/row/row0sel.c
View file

@ -427,11 +427,7 @@ row_sel_fetch_columns(
/* data == NULL means that the
externally stored field was not
written yet. This is only a valid
condition when the server crashed
after the time a record stub was
freshly inserted but before all its
columns were written. This record
written yet. This record
should only be seen by
recv_recovery_rollback_active() or any
TRX_ISO_READ_UNCOMMITTED
@ -2744,12 +2740,7 @@ row_sel_store_mysql_rec(
if (UNIV_UNLIKELY(!data)) {
/* The externally stored field
was not written yet. This is
only a valid condition when
the server crashed after the
time a record stub was freshly
inserted but before all its
columns were written. This
was not written yet. This
record should only be seen by
recv_recovery_rollback_active()
or any TRX_ISO_READ_UNCOMMITTED
@ -3623,8 +3614,7 @@ row_search_for_mysql(
if (!row_sel_store_mysql_rec(buf, prebuilt,
rec, offsets)) {
/* Only fresh inserts at
server crash time may contain
/* Only fresh inserts may contain
incomplete externally stored
columns. Pretend that such
records do not exist. Such
@ -3636,10 +3626,6 @@ row_search_for_mysql(
at a lower level, not here. */
ut_a(trx->isolation_level
== TRX_ISO_READ_UNCOMMITTED);
/* TODO: assert that there is
an owner_trx with
owner_trx->id == DB_TRX_ID and
owner_trx->is_recovered */
err = DB_TOO_BIG_RECORD;
@ -4422,16 +4408,14 @@ requires_clust_rec:
if (!row_sel_push_cache_row_for_mysql(prebuilt, result_rec,
offsets)) {
/* Only fresh inserts at server crash time may contain
incomplete externally stored columns. Pretend that
such records do not exist. Such records may only be
accessed at the READ UNCOMMITTED isolation level or
when rolling back a recovered transaction. Rollback
happens at a lower level, not here. */
/* Only fresh inserts may contain incomplete
externally stored columns. Pretend that such
records do not exist. Such records may only be
accessed at the READ UNCOMMITTED isolation
level or when rolling back a recovered
transaction. Rollback happens at a lower
level, not here. */
ut_a(trx->isolation_level == TRX_ISO_READ_UNCOMMITTED);
/* TODO: assert that there is an owner_trx
with owner_trx->id == DB_TRX_ID and
owner_trx->is_recovered */
} else if (prebuilt->n_fetch_cached
== MYSQL_FETCH_CACHE_SIZE) {
@ -4449,19 +4433,16 @@ requires_clust_rec:
} else {
if (!row_sel_store_mysql_rec(buf, prebuilt,
result_rec, offsets)) {
/* Only fresh inserts at server crash
time may contain incomplete externally
stored columns. Pretend that such
records do not exist. Such records may
only be accessed at the READ UNCOMMITTED
/* Only fresh inserts may contain
incomplete externally stored
columns. Pretend that such records do
not exist. Such records may only be
accessed at the READ UNCOMMITTED
isolation level or when rolling back a
recovered transaction. Rollback happens
at a lower level, not here. */
recovered transaction. Rollback
happens at a lower level, not here. */
ut_a(trx->isolation_level
== TRX_ISO_READ_UNCOMMITTED);
/* TODO: assert that there is an owner_trx
with owner_trx->id == DB_TRX_ID and
owner_trx->is_recovered */
goto next_rec;
}
}