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Bug#57799 READ UNCOMMITTED access failure of off-page DYNAMIC or COMPRESSED

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columns again

This is follow-up to Bug #54358. Not all occurrences of the bug were fixed.
We need to check all calls to btr_copy_externally_stored_field_prefix_low()
and do the right thing when the pointer to the off-page column is null
(full of zero bytes).

It turns out that only the call to btr_copy_externally_stored_field_prefix()
in row_sel_sec_rec_is_for_blob() needs to be changed.

For fetching complete off-page columns rather than prefixes, the function
btr_rec_copy_externally_stored_field() already checks if the pointer
is null (all-zero).  Two of its callers (row_merge_copy_blobs() and
row_sel_fetch_columns()) are never executed as READ COMMITTED and can
rightfully assert that the fetch succeeded.  The third caller,
row_sel_store_mysql_rec(), already does the right thing.

The calls in row_upd_ext_fetch() and trx_undo_page_fetch_ext() must
expect that the off-page column exists. Update and rollback are
locking operations, never READ UNCOMMITTED.
This commit is contained in:
Marko Mäkelä 2010-11-02 09:28:48 +02:00
commit 004bb1b15e
2 changed files with 18 additions and 0 deletions
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12
storage/innodb_plugin/row/row0sel.c
View file

@ -106,6 +106,18 @@ row_sel_sec_rec_is_for_blob(
ulint len;
byte buf[DICT_MAX_INDEX_COL_LEN];
ut_a(clust_len >= BTR_EXTERN_FIELD_REF_SIZE);
if (UNIV_UNLIKELY
(!memcmp(clust_field + clust_len - BTR_EXTERN_FIELD_REF_SIZE,
field_ref_zero, BTR_EXTERN_FIELD_REF_SIZE))) {
/* 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. */
return(FALSE);
}
len = btr_copy_externally_stored_field_prefix(buf, sizeof buf,
zip_size,
clust_field, clust_len);