3 // This File contructs a PostgreSQL trigger.
6 // dupecheck(debug, column1, column2, ...);
8 // debug: if "yes" dupecheck generates debug output
9 // columns: the names of the columns that are used to calculate the
13 // The trigger is normally fired BEFORE an INSERT or UPDATE of an
14 // article or comment. It first calculates a CRC-32 checksum of the
15 // specified columns of the row to be inserted or updated and
16 // checks whether there exists already another row with the same
17 // checksum. In this case, the trigger returns NULL and thus,
18 // aborts the SQL command.
20 // Author: Matthias Jordan <mjordan@code-fu.de>
24 #include "executor/spi.h"
25 #include "commands/trigger.h"
31 extern Datum dupecheck(PG_FUNCTION_ARGS);
32 PG_FUNCTION_INFO_V1(dupecheck);
34 extern Datum dupecheck(void);
46 // crc32 table based on the following polynom
47 #define CRC32_POLY 0x04c11db7 /* AUTODIN II, Ethernet, & FDDI */
49 u_long crc32_table[256] =
50 {0x0000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9, 0x130476dc, 0x17c56b6b,
51 0x1a864db2, 0x1e475005, 0x2608edb8, 0x22c9f00f, 0x2f8ad6d6, 0x2b4bcb61,
52 0x350c9b64, 0x31cd86d3, 0x3c8ea00a, 0x384fbdbd, 0x4c11db70, 0x48d0c6c7,
53 0x4593e01e, 0x4152fda9, 0x5f15adac, 0x5bd4b01b, 0x569796c2, 0x52568b75,
54 0x6a1936c8, 0x6ed82b7f, 0x639b0da6, 0x675a1011, 0x791d4014, 0x7ddc5da3,
55 0x709f7b7a, 0x745e66cd, 0x9823b6e0, 0x9ce2ab57, 0x91a18d8e, 0x95609039,
56 0x8b27c03c, 0x8fe6dd8b, 0x82a5fb52, 0x8664e6e5, 0xbe2b5b58, 0xbaea46ef,
57 0xb7a96036, 0xb3687d81, 0xad2f2d84, 0xa9ee3033, 0xa4ad16ea, 0xa06c0b5d,
58 0xd4326d90, 0xd0f37027, 0xddb056fe, 0xd9714b49, 0xc7361b4c, 0xc3f706fb,
59 0xceb42022, 0xca753d95, 0xf23a8028, 0xf6fb9d9f, 0xfbb8bb46, 0xff79a6f1,
60 0xe13ef6f4, 0xe5ffeb43, 0xe8bccd9a, 0xec7dd02d, 0x34867077, 0x30476dc0,
61 0x3d044b19, 0x39c556ae, 0x278206ab, 0x23431b1c, 0x2e003dc5, 0x2ac12072,
62 0x128e9dcf, 0x164f8078, 0x1b0ca6a1, 0x1fcdbb16, 0x018aeb13, 0x54bf6a4,
63 0x0808d07d, 0x0cc9cdca, 0x7897ab07, 0x7c56b6b0, 0x71159069, 0x75d48dde,
64 0x6b93dddb, 0x6f52c06c, 0x6211e6b5, 0x66d0fb02, 0x5e9f46bf, 0x5a5e5b08,
65 0x571d7dd1, 0x53dc6066, 0x4d9b3063, 0x495a2dd4, 0x44190b0d, 0x40d816ba,
66 0xaca5c697, 0xa864db20, 0xa527fdf9, 0xa1e6e04e, 0xbfa1b04b, 0xbb60adfc,
67 0xb6238b25, 0xb2e29692, 0x8aad2b2f, 0x8e6c3698, 0x832f1041, 0x87ee0df6,
68 0x99a95df3, 0x9d684044, 0x902b669d, 0x94ea7b2a, 0xe0b41de7, 0xe4750050,
69 0xe9362689, 0xedf73b3e, 0xf3b06b3b, 0xf771768c, 0xfa325055, 0xfef34de2,
70 0xc6bcf05f, 0xc27dede8, 0xcf3ecb31, 0xcbffd686, 0xd5b88683, 0xd1799b34,
71 0xdc3abded, 0xd8fba05a, 0x690ce0ee, 0x6dcdfd59, 0x608edb80, 0x644fc637,
72 0x7a089632, 0x7ec98b85, 0x738aad5c, 0x774bb0eb, 0x4f040d56, 0x4bc510e1,
73 0x46863638, 0x42472b8f, 0x5c007b8a, 0x58c1663d, 0x558240e4, 0x51435d53,
74 0x251d3b9e, 0x21dc2629, 0x2c9f00f0, 0x285e1d47, 0x36194d42, 0x32d850f5,
75 0x3f9b762c, 0x3b5a6b9b, 0x0315d626, 0x07d4cb91, 0x0a97ed48, 0xe56f0ff,
76 0x1011a0fa, 0x14d0bd4d, 0x19939b94, 0x1d528623, 0xf12f560e, 0xf5ee4bb9,
77 0xf8ad6d60, 0xfc6c70d7, 0xe22b20d2, 0xe6ea3d65, 0xeba91bbc, 0xef68060b,
78 0xd727bbb6, 0xd3e6a601, 0xdea580d8, 0xda649d6f, 0xc423cd6a, 0xc0e2d0dd,
79 0xcda1f604, 0xc960ebb3, 0xbd3e8d7e, 0xb9ff90c9, 0xb4bcb610, 0xb07daba7,
80 0xae3afba2, 0xaafbe615, 0xa7b8c0cc, 0xa379dd7b, 0x9b3660c6, 0x9ff77d71,
81 0x92b45ba8, 0x9675461f, 0x8832161a, 0x8cf30bad, 0x81b02d74, 0x857130c3,
82 0x5d8a9099, 0x594b8d2e, 0x5408abf7, 0x50c9b640, 0x4e8ee645, 0x4a4ffbf2,
83 0x470cdd2b, 0x43cdc09c, 0x7b827d21, 0x7f436096, 0x7200464f, 0x76c15bf8,
84 0x68860bfd, 0x6c47164a, 0x61043093, 0x65c52d24, 0x119b4be9, 0x155a565e,
85 0x18197087, 0x1cd86d30, 0x029f3d35, 0x065e2082, 0x0b1d065b, 0xfdc1bec,
86 0x3793a651, 0x3352bbe6, 0x3e119d3f, 0x3ad08088, 0x2497d08d, 0x2056cd3a,
87 0x2d15ebe3, 0x29d4f654, 0xc5a92679, 0xc1683bce, 0xcc2b1d17, 0xc8ea00a0,
88 0xd6ad50a5, 0xd26c4d12, 0xdf2f6bcb, 0xdbee767c, 0xe3a1cbc1, 0xe760d676,
89 0xea23f0af, 0xeee2ed18, 0xf0a5bd1d, 0xf464a0aa, 0xf9278673, 0xfde69bc4,
90 0x89b8fd09, 0x8d79e0be, 0x803ac667, 0x84fbdbd0, 0x9abc8bd5, 0x9e7d9662,
91 0x933eb0bb, 0x97ffad0c, 0xafb010b1, 0xab710d06, 0xa6322bdf, 0xa2f33668,
92 0xbcb4666d, 0xb8757bda, 0xb5365d03, 0xb1f740b4};
95 static u_long crc32(u_char *buf, unsigned len)
100 crc = 0xffffffff; /* preload shift register, per CRC-32 spec */
101 for (p = buf; len > 0; ++p, --len)
103 crc = (crc << 8) ^ crc32_table[(crc >> 24) ^ *p];
105 return ~crc; /* transmit complement, per CRC-32 spec */
121 Datum dupecheck(PG_FUNCTION_ARGS)
123 TriggerData *trigdata = (TriggerData *) fcinfo->context;
125 Datum dupecheck(void)
127 TriggerData *trigdata = CurrentTriggerData;
133 int ret = 0, i, fnumber;
134 u_long rowstrlen = 0,
136 char **items, // will point to a malloc'ed array
145 /* Make sure trigdata is pointing at what I expect */
147 if (!CurrentTriggerData)
149 if (!CALLED_AS_TRIGGER(fcinfo))
151 elog(ERROR, "dupecheck: not fired by trigger manager");
152 /* tuple to return to Executor */
153 if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
154 rettuple = trigdata->tg_newtuple;
156 rettuple = trigdata->tg_trigtuple;
158 if (TRIGGER_FIRED_BY_DELETE(trigdata->tg_event))
159 return PointerGetDatum(NULL);
162 // Initialize arguments and see whether the arguments are ok.
163 args = trigdata->tg_trigger->tgargs;
164 nargs = trigdata->tg_trigger->tgnargs;
168 elog(DEBUG, "dupecheck: USAGE: dupeckeck(debug, col1, col2, ...)");
169 return PointerGetDatum(NULL);
172 debug_on = !strcmp("yes", args[0]);
174 tupdesc = trigdata->tg_relation->rd_att;
176 /* Connect to SPI manager */
177 if ((ret = SPI_connect()) != SPI_OK_CONNECT)
179 elog(NOTICE, "dupecheck: SPI_connect returned error %d", ret);
182 // Now we are connected to the database's SPI manager
183 // We will now construct a string of some important row values.
184 // First, we determine how long the string will be to allocate memory
185 // To include an additional item, add another SPI_getvalue line and
186 // increase maxitems above by 1
189 // Allocate array for the argument pointers
190 nitems = nargs - 1; // don't take the debug parameter as a row name;
191 items = (char **) malloc(sizeof(char*) * nitems);
195 return PointerGetDatum(NULL);
199 for (i = 1; (i < nargs); i++)
201 items[i-1] = SPI_getvalue(rettuple, tupdesc, SPI_fnumber(tupdesc, args[i]));
204 elog(DEBUG, "dupecheck: Argument %d: row %s -> %s\n", i, args[i], items[i-1]);
209 // Find out length of row string to be constructed
210 for (i=0; (i < nitems); i++)
212 if (items[i] != NULL)
214 rowstrlen += strlen(items[i]);
218 rowstring = malloc(rowstrlen+1); // add space for 0-terminator
219 if (rowstring == NULL)
223 return PointerGetDatum(NULL);
226 // Construct row string
228 for (i=0; (i < nitems); i++)
230 if (items[i] != NULL)
232 strcat(rowstring, items[i]);
236 // rowstring now contains the data of the maxitems important
237 // items of the table record. Now we calculate the CRC-32 checksum
240 crc = crc32(rowstring, rowstrlen);
242 // Now we allocate some space and construct the SQL query
243 relation = SPI_getrelname(trigdata->tg_relation);
244 query = malloc(40 + strlen(relation) + 11 + 2 + 1); // SELECT part + relation + crc32 + "';" + 0-term
251 return PointerGetDatum(NULL);
254 sprintf(query, "SELECT count(*) FROM %s WHERE checksum='%ld';", relation, crc);
255 ret = SPI_exec(query, 2);
256 num = SPI_getbinval(SPI_tuptable->vals[0], SPI_tuptable->tupdesc, 1, &isnull);
257 elog(DEBUG, "dupecheck: %s", query);
259 if ((ret == SPI_OK_SELECT) && (num > 0) && !(TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event)))
261 elog(NOTICE, "dupecheck: UBD in %s detected, dupe dropped", relation);
262 rettuple = NULL; // reject operation
266 // The checksum wasn't found. So we modify the tuple to be
267 // inserted and add the fresh checksum.
274 elog(NOTICE, "dupecheck: Adding checksum to row");
276 attnum = SPI_fnumber(tupdesc, "checksum");
278 rettuple = SPI_modifytuple(trigdata->tg_relation, rettuple, 1, &attnum, &value, &nulls);
285 return PointerGetDatum(rettuple);