Updated comments. No code changes.

FossilOrigin-Name: e842ad391e62df273a5b1ed569d42ea46d03a99b

manifest

@@ -1,5 +1,5 @@
-C Add\sthe\sOP_SqlExec\sopcode\sand\suse\sit\sto\simplement\s"PRAGMA\sanalyze_as_needed",\ninvoking\sANALYZE\ssubcommands\sas\snecessary.\s\sThis\ssimplifies\sthe\simplementation.
-D 2017-02-18T15:58:52.451
+C Updated\scomments.\s\sNo\scode\schanges.
+D 2017-02-18T22:52:40.654
 F Makefile.in edb6bcdd37748d2b1c3422ff727c748df7ffe918
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc a89ea37ab5928026001569f056973b9059492fe2
@@ -387,7 +387,7 @@ F src/parse.y 591704fce84f814d9a3642774c1f011d38f4149c
 F src/pcache.c 62835bed959e2914edd26afadfecce29ece0e870
 F src/pcache.h 2cedcd8407eb23017d92790b112186886e179490
 F src/pcache1.c e3967219b2a92b9edcb9324a4ba75009090d3953
-F src/pragma.c 1ed159f6fed5af7f5b095f55bdefcb0848956397
+F src/pragma.c 8a35509e8f60746fbdcde5312ddfd177c46c7e9c
 F src/pragma.h 065e184494f12e94111da1ab6984faa7b6142e68
 F src/prepare.c b1140c3d0cf59bc85ace00ce363153041b424b7a
 F src/printf.c 67427bbee66d891fc6f6f5aada857e9cdb368c1c
@@ -1557,7 +1557,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 4229caec0b60a1617b9d5ff94b47271cbd7be1e0
-R 03be76497e56750b0101f816e3587990
+P d386015f5e7ecdd951d70db56b7bbd858be7ad90
+R bb5056af5425096e2e052e924ae83b2e
 U drh
-Z 8d178351b984357dd4d18d50fe476798
+Z a573182d78be17d037798d5840f110fc

manifest.uuid

@@ -1 +1 @@
-d386015f5e7ecdd951d70db56b7bbd858be7ad90
+e842ad391e62df273a5b1ed569d42ea46d03a99b

src/pragma.c

@@ -1830,16 +1830,33 @@ void sqlite3Pragma(
 
   /*
   **  PRAGMA analyze_as_needed
+  **  PRAGMA schema.analyze_as_needed
+  **
+  ** This pragma runs ANALYZE on any tables which would have benefitted
+  ** from having recent statistics at some point since the start of the
+  ** current connection.  Only tables in "schema" are analyzed in the 
+  ** second form.  In the first form, all tables except TEMP tables are
+  ** checked.
+  **
+  ** A table is analyzed only if both of the following are true:
+  **
+  ** (1) The query planner used sqlite_stat1-style statistics for one or
+  **     more indexes of the table at some point during the lifetime of
+  **     the current connection.
+  **
+  ** (2) One or more indexes of the table are currently unanalyzed OR
+  **     the number of rows in the table has increased by 25 times or more
+  **     since the last time ANALYZE was run.
   */
   case PragTyp_ANALYZE_AS_NEEDED: {
-    int iDbLast;
-    int iTabCur;
-    HashElem *k;
-    Schema *pSchema;
-    Table *pTab;
-    Index *pIdx;
-    LogEst szThreshold;
-    char *zSubSql;
+    int iDbLast;           /* Loop termination point for the schema loop */
+    int iTabCur;           /* Cursor for a table whose size needs checking */
+    HashElem *k;           /* Loop over tables of a schema */
+    Schema *pSchema;       /* The current schema */
+    Table *pTab;           /* A table in the schema */
+    Index *pIdx;           /* An index of the table */
+    LogEst szThreshold;    /* Size threshold above which reanalysis is needd */
+    char *zSubSql;         /* SQL statement for the OP_SqlExec opcode */
 
     iTabCur = pParse->nTab++;
     for(iDbLast = zDb?iDb:db->nDb-1; iDb<=iDbLast; iDb++){
@@ -1848,11 +1865,17 @@ void sqlite3Pragma(
       pSchema = db->aDb[iDb].pSchema;
       for(k=sqliteHashFirst(&pSchema->tblHash); k; k=sqliteHashNext(k)){
         pTab = (Table*)sqliteHashData(k);
+
+        /* If table pTab has not been used in a way that would benefit from
+        ** having analysis statistics during the current session, then skip it.
+        ** This also has the effect of skipping virtual tables and views */
         if( (pTab->tabFlags & TF_StatsUsed)==0 ) continue;
+
+        /* Reanalyze if the table is 25 times larger than the last analysis */
         szThreshold = pTab->nRowLogEst + 46; assert( sqlite3LogEst(25)==46 );
         for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
           if( !pIdx->hasStat1 ){
-            szThreshold = 0;
+            szThreshold = 0; /* Always analyze if any index lacks statistics */
             break;
           }
         }