&ctl, HASH_ELEM | HASH_BLOBS); dlist_init(&unowned_relns); } /* Look up or create an entry */ brlocator.locator = rlocator; brlocator.backend = backend; reln = (SMgrRelation) hash_search(SMgrRelationHash, &brlocator, HASH_ENTER, &found); /* Initialize it if not present before ...
Hash in Postgres:postgres中的hash是动态hash,相关实现在dynahash.c中。pg中的动态哈希表既可以支持单个backend使用又可以支持在共享内存中跨backend使用。使用动态哈希表时,需要调用者来管理锁的问题。最简单的方式是使用一个LWLock来保护整个hashtable。查询(HASH_FIND或者hash_seq_search)只需要持有共享锁,更新操作...
* This does not attempt to actually open the underlying file. */SMgrRelationsmgropen(RelFileLocator rlocator,BackendId backend){RelFileLocatorBackend brlocator;SMgrRelation reln;bool found;if(SMgrRelationHash==NULL){/* First time through: initialize the hash table */HASHCTLctl;ctl.keysize=sizeof...
|_gin(Gerneralized Inverted Index通用逆向索引) |_gist(Gerneralized Search Tree通用索引) |_hash(哈希索引) |_heap(heap的访问方法) |_bootstrap---数据库的初始化处理(initdb) |_catalog---系统目录 |_commands---select/insert/update/delete以外的SQL命令 |_common.mk--- |_executor---执行器(访问的...
Hash索引 特点:使用哈希函数将键映射到索引条目,因此只能用于等值查询,不支持范围查询和排序操作。 使用场景:适用于数据分布均匀且查询条件为单一值的场景。 GiST索引 特点:广义搜索树(Generalized Search Tree)索引,支持多种索引策略和自定义搜索算法,适用于多种类型数据的搜索和查询场景,如几何数据、空间数据等。
配置search_path路径,为了能够找到schema的表等等 AI检测代码解析 denali=# \dt region_longlive No matching relations found. denali=# SHOW search_path denali-# ; search_path --- "$user", public (1 row)denali=# set search_path to region_longlive,public; SET denali=# SHOW search...
http://192.168.56.10:9200/ { "name" : "8448ec5f3312", "cluster_name" : "elasticsearch", "cluster_uuid" : "xC72O3nKSjWavYZ-EPt9Gw", "version" : { "number" : "7.4.2", "build_flavor" : "default", "build_type" : "docker", "build_hash" : "2f90bbf7b93631e52bafb59b3b049cb...
PostgreSQL提供了多 种索引类型:B-Tree、Hash、GiST和GIN,由于它们使用了不同的算法,因此每种索引类型都有其适合的查询类型,缺省时,CREATE INDEX命令将创建B-Tree索引。6.1.1 B-TreeCREATE TABLE test1 ( id integer, content varchar ); CREATE INDEX test1_id_index ON test1 (id); B-Tree索引主要用于...
This can provide fast, exact nearest neighbor search in many cases. Postgres has a number of index types for this: B-tree (default), hash, GiST, SP-GiST, GIN, and BRIN.CREATE INDEX ON items (category_id);For multiple columns, consider a multicolumn index....
In place of Oracle’s CREATE SYNONYM for accessing remote objects, Postgres has you use SET search_path to include the remote definition. Oracle: CREATE SYNONYM abc.mytable FOR xyz.mytable; Postgres: SET search_path TO 'abc.mytable'; 17. SYSDATEOracle's SYSDATE function ...