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Merge of HACKING from jahlborn

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Nirgal Vourgère
2013-07-01 14:41:12 +02:00
parent 6b24b25454 314e6040c5
commit 54a036d8b2
1 changed files with 58 additions and 21 deletions
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HACKING
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@@ -242,6 +242,11 @@ Number of characters in a Memo field: 65,535 when entering data through the
user interface; 2 gigabytes of character storage when entering data
programmatically. That would mean 31 bits for length.
Note: if a memo field is marked for compression, only at value which is at
most 1024 characters when uncompressed can be compressed. fields longer than
that _must_ be stored uncompressed.
LVAL (Long Value) Pages
-----------------------
@@ -306,7 +311,7 @@ next_pg field.
| ???? | 2 bytes | max_cols | Max columns a row will have (deletions) |
| ???? | 2 bytes | num_var_cols| Number of variable columns in table |
| ???? | 2 bytes | num_cols | Number of columns in table (repeat) |
| ???? | 4 bytes | num_idx | Number of indexes in table |
| ???? | 4 bytes | num_idx | Number of logical indexes in table |
| ???? | 4 bytes | num_real_idx| Number of index entries |
| ???? | 4 bytes | used_pages | Points to a record containing the |
| | | | usage bitmask for this table. |
@@ -337,14 +342,14 @@ next_pg field.
| ???? | 1 byte | col_name_len| len of the name of the column |
| ???? | n bytes | col_name | Name of the column |
+-------------------------------------------------------------------------+
| Iterate for indexes with index_type 0 or 1 (30+9 = 39 bytes) |
| Iterate for the number of num_real_idx (30+9 = 39 bytes) |
+-------------------------------------------------------------------------+
| Iterate 10 times for 10 possible columns (10*3 = 30 bytes) |
+-------------------------------------------------------------------------+
| ???? | 2 bytes | col_num | number of a column (0xFFFF= none) |
| ???? | 1 byte | col_order | 0x01 = ascendency order |
+-------------------------------------------------------------------------+
| ???? | 4 bytes | unknown | |
| ???? | 4 bytes | used_pages | Points to usage bitmap for index |
| ???? | 4 bytes | first_dp | Data pointer of the index page |
| ???? | 1 byte | flags | See flags table for indexes |
+-------------------------------------------------------------------------+
@@ -353,11 +358,14 @@ next_pg field.
| ???? | 4 bytes | index_num | Number of the index |
| | | |(warn: not always in the sequential order)|
| ???? | 4 bytes | index_num2 | Index into index cols list |
| 0x00 | 1 byte | ??? | |
| 0xFF | 4 bytes | ??? | |
| 0x00 | 4 bytes | ??? | |
| 0x04 | 2 bytes | ??? | |
| ???? | 1 byte | primary_key | 0x01 if this index is primary |
| 0x00 | 1 byte | rel_tbl_type| type of the other table in this fk |
| | | | (same values as index_type) |
| 0xFF | 4 bytes | rel_idx_num | index number of other index in fk |
| | | | (or -1 if this index is not a fk) |
| 0x00 | 4 bytes | rel_tbl_page| page number of other table in fk |
| 0x01 | 1 byte | cascade_ups | flag indicating if updates are cascaded |
| 0x01 | 1 byte | cascade_dels| flag indicating if deletes are cascaded |
| ???? | 1 byte | index_type | 0x01 if index is primary, 0x02 if foreign|
+-------------------------------------------------------------------------+
| Iterate for the number of num_idx |
+-------------------------------------------------------------------------+
@@ -367,8 +375,10 @@ next_pg field.
| Iterate while col_num != 0xffff |
+-------------------------------------------------------------------------+
| ???? | 2 bytes | col_num | Column number with variable length |
| ???? | 4 bytes | arg1 | |
| ???? | 4 bytes | arg2 | |
| ???? | 4 bytes | used_pages | Points to a record containing the |
| | | | usage bitmask for this column. |
| ???? | 4 bytes | free_pages | Points to a similar record as above, |
| | | | listing pages which contain free space. |
+-------------------------------------------------------------------------+
+-------------------------------------------------------------------------+
@@ -390,7 +400,7 @@ next_pg field.
| ???? | 2 bytes | max_cols | Max columns a row will have (deletions) |
| ???? | 2 bytes | num_var_cols| Number of variable columns in table |
| ???? | 2 bytes | num_cols | Number of columns in table (repeat) |
| ???? | 4 bytes | num_idx | Number of indexes in table |
| ???? | 4 bytes | num_idx | Number of logical indexes in table |
| ???? | 4 bytes | num_real_idx| Number of index entries |
| ???? | 4 bytes | used_pages | Points to a record containing the |
| | | | usage bitmask for this table. |
@@ -425,7 +435,7 @@ next_pg field.
| ???? | 2 bytes | col_name_len| len of the name of the column |
| ???? | n bytes | col_name | Name of the column (UCS-2 format) |
+-------------------------------------------------------------------------+
| Iterate for indexes with index_type 0 or 1 (30+22 = 52 bytes) |
| Iterate for the number of num_real_idx (30+22 = 52 bytes) |
+-------------------------------------------------------------------------+
| ???? | 4 bytes | ??? | |
+-------------------------------------------------------------------------+
@@ -434,7 +444,7 @@ next_pg field.
| ???? | 2 bytes | col_num | number of a column (0xFFFF= none) |
| ???? | 1 byte | col_order | 0x01 = ascendency order |
+-------------------------------------------------------------------------+
| ???? | 4 bytes | unknown | |
| ???? | 4 bytes | used_pages | Points to usage bitmap for index |
| ???? | 4 bytes | first_dp | Data pointer of the index page |
| ???? | 1 byte | flags | See flags table for indexes |
| ???? | 9 bytes | unknown | |
@@ -445,12 +455,14 @@ next_pg field.
| ???? | 4 bytes | index_num | Number of the index |
| | | |(warn: not always in the sequential order)|
| ???? | 4 bytes | index_num2 | Index into index cols list |
| 0x00 | 1 byte | ??? | |
| 0xFF | 4 bytes | ??? | |
| 0x00 | 4 bytes | ??? | |
| 0x04 | 2 bytes | ??? | |
| ???? | 1 byte | primary_key | 0x01 if this index is primary |
| ???? | 4 bytes | unknown | |
| 0x00 | 1 byte | rel_tbl_type| type of the other table in this fk |
| | | | (same values as index_type) |
| 0xFF | 4 bytes | rel_idx_num | index number of other index in fk |
| | | | (or -1 if this index is not a fk) |
| 0x00 | 4 bytes | rel_tbl_page| page number of other table in fk |
| 0x01 | 1 byte | cascade_ups | flag indicating if updates are cascaded |
| 0x01 | 1 byte | cascade_dels| flag indicating if deletes are cascaded |
| ???? | 1 byte | index_type | 0x01 if index is primary, 0x02 if foreign|
+-------------------------------------------------------------------------+
| Iterate for the number of num_idx |
+-------------------------------------------------------------------------+
@@ -460,8 +472,10 @@ next_pg field.
| Iterate while col_num != 0xffff |
+-------------------------------------------------------------------------+
| ???? | 2 bytes | col_num | Column number with variable length |
| ???? | 4 bytes | arg1 | |
| ???? | 4 bytes | arg2 | |
| ???? | 4 bytes | used_pages | Points to a record containing the |
| | | | usage bitmask for this column. |
| ???? | 4 bytes | free_pages | Points to a similar record as above, |
| | | | listing pages which contain free space. |
+-------------------------------------------------------------------------+
Columns flags (not complete):
@@ -500,6 +514,29 @@ Column Type may be one of the following (not complete):
REPID = 0x0F /* GUID */
NUMERIC = 0x10 /* Scaled decimal (17 bytes) */
Notes on reading index metadata:
There are 2 types of index metadata, "physical" index info (denoted by
num_real_idx) and "logical" index info (denoted by num_idx). Normally, there
is a 1 to 1 relationship between these 2 types of information. However there
can be more logical index infos than physical index infos (currently only seen
for foreign key indexes). In this situation, one or more of the logical
indexes actually share the same underlying physical index (the index_num2
indicates which physical index backs which logical index).
As noted in the previous paragraph, physical index sharing is generally only
seen when a foreign key index has been created. When access creates a
relationship between 2 tables with "enforce referential integrity" enabled,
each of the tables gets an extra logical index with type 2 (foreign key).
These logical indexes contain extra information, primarily pointers to the
related table (rel_tbl_page) and logical index (rel_idx_num). Also, the
rel_tbl_type value indicates which table in the relationship is the "primary"
table (the one one from which cascaded updates/deletes flow). If the indexed
columns for the foreign key are already indexed by another logical index in
the table (e.g. an index which the user has explicitly created), then the
logical foreign key index will simply share the underlying physical index
data.
Notes on deleted and added columns: (sort of Jet4 specific)
If a fixed length column is deleted the offset_F field will contain the offsets